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design.md

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`866c7f96` 2026-09-07 Pavel Safronov	1	# Tower — Design
	2
	3	Tower is the setting of a novel. This app exists to serve that: first as an
	4	instrument for the author to see the place and keep it consistent, and second as a
	5	companion piece readers can explore. Where a choice trades spectacle against
	6	coherence, coherence wins — canon here is series-bible material, and the book is
	7	downstream of it.
	8
	9	Tower is a smart cylinder in orbit around Earth, spun for 1 g, with an inner
	10	surface the size of Wisconsin, lit by sunlight piped down its axis and scattered by
	11	a swarm of mirrors it flies itself. It is also a person.
	12
	13	The app has three linked views:
	14
	15	1. Exterior — a 3D render of Tower from outside, with its collector, beam and
	16	orbit. You pick a point on the hull.
	17	2. Map — a 2D unrolled map of the inner surface. You pick a point here too; the
	18	two pickers stay in sync.
	19	3. Interior — a first-person "streetview" from the picked point, with live
	20	controls for time of day and spin phase.
	21
	22	---
	23
	24	## 1. Canon
	25
	26	### 1.1 Dimensions
	27
	28	All numbers derive from two free parameters — radius and length — chosen so the
	29	inner surface matches Wisconsin.
	30
	31	\| Quantity \| Value \| Notes \|
	32	\|---\|---\|---\|
	33	\| Radius \| 50 km \| floor to axis \|
	34	\| Length \| 540 km \| sun cap to far cap \|
`de65ab10` 2026-09-08 Pavel Safronov	35	\| Wall depth \| 1 km \| floor to outer skin, D-044 \|
`866c7f96` 2026-09-07 Pavel Safronov	36	\| Circumference \| 314.16 km \| the world's "width" \|
	37	\| Inner surface area \| 169,646 km² \| Wisconsin total area, 169,635 km² \|
	38	\| Habitable land area \| 169,646 km² \| all of it — the hull is sealed (§1.4) \|
	39
	40	Every square metre of the inner surface is land. There are no windows in the wall,
	41	so nothing is subtracted. *An earlier version sized star slats to leave exactly
	42	Wisconsin's land area of 140,268 km²; D-017 removes them and that second
	43	coincidence with it.*
	44
	45	### 1.2 Spin and gravity
	46
	47	\| Quantity \| Value \|
	48	\|---\|---\|
	49	\| Angular velocity ω \| 0.014005 rad/s \|
	50	\| Spin period \| 448.6 s = 7 min 29 s \|
	51	\| Rotation rate \| 0.134 rpm \|
	52	\| Rim speed \| 700.2 m/s \|
	53	\| Floor gravity \| 1.000 g by construction \|
	54
	55	Consequences that the app should show or at least respect:
	56
	57	- Gravity falls off linearly with height. g(h) = ω²(R−h). A 1 km peak sits at
	58	0.98 g; the axis is weightless. Mirrors at the axis float.
	59	- Coriolis is mild but real. 2ω = 0.0280 s⁻¹. Walking is unaffected (0.4 % g).
	60	A ball thrown at 30 m/s deflects at 8.6 % g — enough that Tower's sports differ
	61	from Earth's, and enough that thrown objects visibly curve.
`769726ea` 2026-09-08 Pavel Safronov	62	- Nothing in the sky moves, except through the far cap. The wall is sealed
	63	(§1.4), so along 539 of the 540 km there is nothing to wheel past — the far side
	64	of the world overhead co-rotates with you and hangs perfectly still. The one
	65	exception is the far cap window, where the sky is outside and does not
	66	co-rotate: it turns once every 7 min 29 s about a single motionless star on the
	67	axis. The spin is invisible upward and obvious deepward, and only at night.
`866c7f96` 2026-09-07 Pavel Safronov	68	- But everything that falls leans. Rain hangs at a permanent 1.47° slant, smoke
	69	drifts the other way, and a 1 km waterfall lands 133 m off its own cliff (§1.9.2).
	70	This inversion is the alien fact the interior view must sell: **the sky is still
	71	and the water is not.**
	72
	73	### 1.3 The sun system
	74
	75	Sunlight enters through the sun-facing end cap and runs the full 540 km axis.
	76
	77	- Collector. A mirror array flies ahead of Tower, gathering sunlight and
	78	concentrating it into the beam. **46,900 km² of aperture — a disc ~244 km
	79	across**, two and a half times Tower's own diameter. It is the dominant visual
	80	element of the exterior view.
	81	- Beam. 10 km in circumference — 1,592 m radius, 7.96 km² cross-section —
	82	carrying 54.3 TW at a concentration of 5,000×, or 6.8 MW/m². It runs the
	83	axis from sun cap to far cap.
	84	- Diffusers. Not lamps — a swarm. See §1.3.1.
	85	- The beam is visible, and it glows by itself. There is real air at the axis
	86	(§1.5), and a 6.8 MW/m² beam Rayleigh-scattering through 3.18 km of it radiates
	87	779 W/m²/sr — **26× brighter than clear blue sky, 25,700× dimmer than the
	88	sun's disc.** It is a brilliantly sunlit cloud extruded into a rod, safe to look
	89	at directly. From the floor 50 km below it is **3.65° wide, about seven
	90	sun-widths**, running the whole length of the sky. This glow is a property of the
	91	beam and the air, not of the diffusers — it would be there if the beam were empty.
	92
`9c891d2e` 2026-09-08 Pavel Safronov	93	#### 1.3.0 Tower never sees the sun
	94
	95	The collector is 244 km across and flies 320 km ahead of the sun cap, which puts
	96	it 41.8° wide in Tower's sky against the sun's 0.53° — **79 times the sun's
	97	diameter**. It sits squarely between Tower and the sun, so it occults it completely,
	98	and the umbra it casts is 120 km across where Tower's 51 km sits inside it. The
	99	eclipse is total, permanent, and self-inflicted.
	100
	101	So nobody aboard can see the sun, for the same reason nobody can see Earth
	102	(§1.4). What they can see, through the sun cap window, is the back of the
	103	collector: 46,938 km² of structure radiating its own waste heat at about 245 K —
	104	infrared, and therefore black. It is the only object in Tower's sky that is neither
	105	Tower nor a star, and it never moves, because the collector flies in formation
	106	rather than spinning. D-050.
	107
`49b0d64d` 2026-09-08 Pavel Safronov	108	Its edge is not black. The face is a mirror pointed away, but the collector is
	109	backlit, and the structure holding 46,938 km² flat stands proud of the mirror
	110	plane at the rim, where the sun strikes it side-on. With the scatter any real mirror
	111	throws at grazing incidence, the edge reads as a thin sun-coloured ring — so the
	112	collector is a hole in the stars with a lit rim rather than an absence, which is how
	113	anything backlit looks. It is not sunlight leaking past the edge: Tower is wholly
	114	inside the umbra, so the sun's disc is hidden from every point in the world. The ring
	115	is lit structure. D-054.
	116
`866c7f96` 2026-09-07 Pavel Safronov	117	#### 1.3.1 The diffuser swarm
	118
	119	The diffusers must be individually invisible, or the sky becomes a row of separate
	120	suns. Two thresholds govern this, and only the second one binds:
	121
	122	- Resolvability. At 50 km, one arcminute is 14.5 m. Anything larger is a
	123	resolved disc with a visible edge.
	124	- Visibility. Being unresolved is not enough — stars are unresolved and we see
	125	them. A mirror preserves radiance, so a mirrorlet aimed at an observer shows
	126	the sun's own surface brightness over a tiny angle. A 1 m mirrorlet reads at
	127	magnitude −13.6, brighter than the full moon. Blending into daylight requires
	128	~1.2 cm, at magnitude −4.0, just under Venus.
	129
	130	Diverting 54.3 TW needs 11.3 km² of mirror, so:
	131
	132	\| \| \|
	133	\|---\|---\|
	134	\| Mirrorlet size \| 1.2 cm, ~1.4 cm², 2 mg \|
	135	\| Count \| 78 billion \|
	136	\| Total mass \| 158 tonnes — the entire sun system \|
	137	\| Mean spacing in beam \| 3.8 m — sparse enough to fly through \|
	138	\| Optical depth over 540 km \| 1.41, so 24 % of light reaches the far cap \|
	139
	140	The swarm cannot be passive — it must fly, always. The axis is not weightless.
	141	At the beam's edge gravity is 0.312 m/s², enough that a foil sinks outward at
	142	0.26 m/s and leaves the beam in 1.7 hours. A drifting swarm dissolves the same
	143	afternoon. Every foil is therefore under continuous individual control. This is not
	144	a flourish on a working system; it is the only configuration that works.
	145
	146	They have absurd power to do it with. Each foil intercepts 979 W of beam.
	147	Harvesting 0.1 % gives it ~1 W on a 2 mg body — 489,600 W/kg, some fifty times
	148	a jet engine's specific power.
	149
	150	\| \| \|
	151	\|---\|---\|
	152	\| Down-beam, riding radiation pressure \| 0.85 m/s, 7.4 days \|
	153	\| Back up-beam under its own power at 1.5 m/s \| 15 µW, 4.2 days \|
	154	\| Harvestable from ambient world-light \| 14,400 µW — a 1000× margin \|
	155
	156	So there is no recirculation machinery, at either cap. The foils fly home on
	157	scavenged daylight. Nothing needs to be built for them, and the 1000× power margin
	158	means Tower can afford to move them wastefully — in spirals, shoals and patterns
	159	that cost energy for no reason but preference.
	160
	161	Lighting is a render target, not a schedule. 78 billion independently aimed
	162	mirrors put any intensity on any patch of ground at any time. Dawn, dusk, moving
	163	cloud shadows and seasons are compositing problems, not optical ones.
	164
`59c12827` 2026-09-28 Pavel Safronov	165	Together they make Tower's sun (D-074). Individually invisible, the swarm gathers
	166	by day into a single shoal on the axis and throws the beam's light out sideways from
	167	there — one blazing point 3.2 km across, which is Tower's sun. The shoal moves: it
	168	forms at the sun cap at sunrise and flies the length of the world by sunset, where it
	169	disperses (§1.3.4). Each mirrorlet in it is aimed, so Tower sends as much of the sun's
	170	light toward ground far away as toward ground beneath it, and the sun looks equally
`f16f084e` 2026-09-28 Pavel Safronov	171	bright from everywhere, as Earth's does; the ground is lit by how high it stands. The
	172	shoal takes only part of the beam and lets the rest run on (D-079), so **the rod glows
	173	from cap to cap at every hour**, a little dimmer past the sun than before it, and ends
	174	on the far cap's mirror. This is the one exception to the rule
`59c12827` 2026-09-28 Pavel Safronov	175	above that the diffusers must never read as a sun: Tower wants exactly one.
	176
`866c7f96` 2026-09-07 Pavel Safronov	177	Aiming resolution is human-sized. A 1.2 cm mirror is diffraction-limited to
	178	4.6×10⁻⁵ rad, so its reflection lands as a 2.3 m spot on the floor 50 km below.
	179	Tower can put a glint on one person that someone five metres away cannot see. The
	180	privacy is set by the wavelength of light, not by any protocol.
	181
	182	Mirrorfall. A failed foil sinks out of the beam and falls. Terminal velocity at
	183	the floor is 0.48 m/s; the descent takes about two days and it lands like a
	184	snowflake. There is a permanent slow glitter coming down out of Tower's sky.
	185
	186	#### Illumination is a dial, not a constant
	187
	188	54.3 TW is Tower's capability, not its setting. Spread over the inner surface it
	189	is 320 W/m² mean, which — with roughly half the surface lit at a time and a
	190	sinusoidal day profile — puts **local noon at ~1,000 W/m², Earth clear-sky
	191	daylight**. But the diffusers are software-controlled, so brightness is genuinely
	192	adjustable in-world across the full range:
	193
	194	\| Setting \| Mean W/m² \| Feels like \|
	195	\|---\|---\|---\|
	196	\| Twilight \| 30 \| permanent overcast dusk \|
	197	\| Temperate \| 200 \| Earth's global mean \|
	198	\| Full \| 320 \| Earth clear-sky noon \|
	199
	200	This should be a control in the app, not a fixed number. It is the most
	201	characterful thing about a world whose sun is a machine.
	202
	203	#### Headroom
	204
	205	5,000× is 11 % of the étendue limit (46,223× at 1 AU). Tower could in principle
	206	push the beam 9.2× further and cook itself; the diffuser network is as much a safety
	207	system as a lighting system. 5,000× was chosen because it is demonstrated
	208	technology — the Odeillo solar furnace reaches ~10 MW/m² on Earth today. Nothing in
	209	Tower's sun system requires physics that does not exist. See `decisions.md` D-003.
	210
`392bb8a7` 2026-09-08 Pavel Safronov	211	#### 1.3.2 Night, and the difference between banked and off
	212
`59c12827` 2026-09-28 Pavel Safronov	213	Night is the sun going out and the beam banked (D-074). The sun reaches the far
	214	cap at sunset and the shoal disperses; the beam is then banked for the night, and
	215	comes back up for the sun to light at the sun cap in the morning. Banking is not
	216	optional, for the reason below.
	217
`392bb8a7` 2026-09-08 Pavel Safronov	218	Night cannot be made by aiming the swarm away. The glow above belongs to the
	219	beam and the air, not to the diffusers, so a fully lit beam lights the world
	220	whatever the mirrorlets are doing: 779 W/m²/sr over a strip 3.65° wide running
	221	horizon to horizon is about 0.2 sr, which lands ~100 W/m² on the floor — half
	222	of temperate, and no kind of night. Tower's night is therefore made by **banking
	223	the beam itself, to a thousandth of full: 0.32 W/m²**, a rod you can still find
	224	overhead and a world you can just make out under it (D-046).
	225
	226	Shutting the beam down entirely is a different state and a much worse one. No
	227	airlight, no lit ground, no rod — the only thing left in the world is the sky
	228	through the far cap. §1.9.4 gives the thermal mass about a week of coasting, so
	229	this is a state Tower can survive and not one it can sit in.
	230
	231	\| Setting \| Floor \| What it is \|
	232	\|---\|---\|---\|
	233	\| Dark \| 0 \| the beam shut down. Stars, and nothing else. \|
	234	\| Night \| 0.32 W/m² \| the beam banked to a thousandth \|
`42b4554e` 2026-09-29 Pavel Safronov	235	\| Moonlit night \| up to 0.64 W/m² \| the same, and a full moon's light again (§1.3.5) \|
`392bb8a7` 2026-09-08 Pavel Safronov	236	\| Twilight \| 30 W/m² \| \|
	237	\| Temperate \| 200 W/m² \| \|
	238	\| Full \| 320 W/m² \| Earth clear-sky noon \|
	239
`da6bcb0e` 2026-09-08 Pavel Safronov	240	#### 1.3.3 The far cap mirror, and where the last quarter of the beam goes
	241
`f16f084e` 2026-09-28 Pavel Safronov	242	Since D-079 the mirror is lit at every hour. By day the sun's shoal takes part of the
	243	beam where it is and lets the rest run on to the far cap; by night the mirror works on the
	244	banked beam. The rod always ends on it.
`59c12827` 2026-09-28 Pavel Safronov	245
`da6bcb0e` 2026-09-08 Pavel Safronov	246	The swarm has optical depth 1.41, so 24% of the beam survives all 540 km — and
	247	it survives collimated, in the beam's own 7.96 km² cross-section. That is the
	248	whole shape of the problem: not 13 TW spread over a 7,854 km² cap, but **1.7 MW/m²
	249	in a 3.2 km spot, about 1,200 suns. An absorber there sits at 2,330 K**.
	250
	251	So the spot is a mirror (D-048), and only the spot: it is a thousandth of the
	252	cap's area, which is what leaves the other 99.9% free to be window (§1.4). A mirror
	253	is the cheap answer rather than the expensive one — at 99.9% it absorbs **1,665
	254	W/m²**, about 1.2 Earth solar constants, so the thing that would have glowed white
	255	is merely warm.
	256
	257	It also recovers the energy. The residual goes back up the column, which makes
	258	the optical path 1,080 km instead of 540 and utilisation 1 - e^(-2τ) = 94%
	259	rather than 76%. What survives even the return trip leaves through the beam
	260	aperture toward the collector, which sends it back again; in the limit the whole
	261	54.3 TW lands on the inner surface. **This is why full brightness is 320 W/m² and
	262	not 243** — the figure in §1.3 assumes the entire beam is eventually used, and with
	263	the cavity closed at both ends it is.
	264
	265	Aiming light at a region to warm it is a separate lever and stays one (§1.9.4). The
	266	mirror is about not wasting the beam; the desert is about where the weather goes.
	267
`59c12827` 2026-09-28 Pavel Safronov	268	#### 1.3.4 The day: a sun that crosses the world
	269
	270	Rewritten for D-074; it replaces the dawn front of D-053.
`2bb3e0de` 2026-09-08 Pavel Safronov	271
	272	Tower's day is 24 hours, chosen for the people living under it — nothing
	273	physical offers one, since the spin is 7.5 minutes and has nothing to do with light.
`de3d60d6` 2026-09-29 Pavel Safronov	274	Tower keeps an Earth city's days: Pisa's (D-089; until then, Sydney's). Its clock is
	275	Pisa's — Italian time, daylight saving included — and its sunrise and sunset are Pisa's,
	276	so the days lengthen and shorten with Pisa's seasons. Day 0 is the northern autumn
	277	equinox, 23 September 2026, so the calendar starts on a 12-hour day and shortens toward
	278	December. The city and that date are the `calendar` in the world file, and can be changed
	279	there. The app's clock opens at Pisa's time now and runs on at the speed it was last run at.
`59c12827` 2026-09-28 Pavel Safronov	280
	281	The sun crosses the world once a day. It lights at the sun cap at sunrise,
	282	travels at a steady speed down the axis, and reaches the far cap at sunset, where
`de3d60d6` 2026-09-29 Pavel Safronov	283	it goes out. At the equinox that is 540 km in 12 hours 11 minutes — 44 km/h, a sun
	284	you can watch move; at midwinter the day is 8 h 55 min and it runs at 61 km/h, and at
	285	midsummer 15 h 27 min and 35 km/h. It takes a quarter of an hour to light and a quarter
`59c12827` 2026-09-28 Pavel Safronov	286	of an hour to go out, which is the shoal gathering and dispersing. Then it is night
	287	(§1.3.2) until the next sunrise.
	288
	289	Every place has its own noon. The sun is 50 km overhead when it passes, so each
	290	place along the world has its midday at a different hour: the sun-cap end in the early
	291	morning, The Capital at about midday, the far-cap end towards evening. Away from
	292	overhead the sun stands lower — 45° at 50 km off, 11° at 270 km — and the ground is lit
	293	by how high it stands (§1.3.1). It never sets: from one cap, the sun at the other is
	294	still 5° up. Morning is a low sun in the sunward sky, evening a low sun deepward. §1.9.4
	295	says Tower has no latitude; the sun gives it longitude, and a direction for its days.
	296
	297	The same sun inside and out. The sun is a point on the beam, lit by the beam, and it
	298	is drawn once and seen by both views — from the floor, and in through the windows from
	299	outside — with the same haze between it and the eye.
`2bb3e0de` 2026-09-08 Pavel Safronov	300
`42b4554e` 2026-09-29 Pavel Safronov	301	#### 1.3.5 The night: a moon
	302
	303	Asked for by the author, 2026-09-28; D-088.
	304
	305	Tower has a moon. By night the swarm gathers a second, smaller shoal on the banked beam,
	306	the size of the sun — 3.2 km, as Earth's Moon and Sun are one size in Earth's sky. It lights
	307	at the far cap as the sun goes out there at dusk, and crosses the world the other way,
	308	sunward, reaching the sun cap by sunrise, where the sun lights behind it. At the equinox
`de3d60d6` 2026-09-29 Pavel Safronov	309	that is 540 km in about 11 h 50 min, some 46 km/h; the long winter nights run it slower.
`42b4554e` 2026-09-29 Pavel Safronov	310
`de3d60d6` 2026-09-29 Pavel Safronov	311	It keeps Earth's Moon's phases, as the sun keeps Pisa's days. Its disc is lit as much as
`42b4554e` 2026-09-29 Pavel Safronov	312	the Moon is lit that night, and shaped like it: the lit part lies toward the far cap while it
	313	waxes — the end the sun went out at, as a waxing moon on Earth is lit on the side of the set
	314	sun — and toward the sun cap while it wanes, the end the sun will light at. The dark part is
	315	not drawn; those mirrorlets are simply turned away. At new moon there is no moon.
	316
	317	It lights the world. At full it throws as much light on the floor as the whole banked rod,
	318	so a full-moon night is twice as bright as a moonless one — 0.64 W/m² against 0.32 — and lit
	319	from one direction, with the land facing it brighter. Tower banks the beam that much less to
	320	feed it. This is a choice and not a necessity: Earth's full moon is about a hundred and
	321	fiftieth of Tower's banked night, and would be lost in it. Water shows a path of moonlight.
	322
`866c7f96` 2026-09-07 Pavel Safronov	323	### 1.4 Sealed hull, and the cap windows
	324
	325	The cylinder wall is opaque and unbroken. No slats, no windows, no view out
	326	along any of the 540 km. From anywhere on the inner surface, the sky is land, haze
	327	and the beam — nothing else. See D-017.
	328
	329	The only views out are at the end caps, and they are peculiar:
	330
	331	- A cap is a wall, not a floor. Gravity there points radially outward, which is
	332	tangent to the cap's surface, so nothing rests on it — you would slide to the
	333	rim. Each cap is a 50 km vertical cliff standing at the end of the world, and
	334	its windows sit at its base, at eye level for anyone standing on the floor.
	335	- The sky through them does not sweep — it turns. A cap window looks along the
	336	spin axis, which is the celestial pole. Stars rotate about a fixed centre, one
	337	full turn every 7.5 minutes, with one motionless star at the middle. **A pinwheel
`769726ea` 2026-09-08 Pavel Safronov	338	sky.** It is the only moving sky anyone in Tower ever sees — and because the axis
	339	is horizontal from the floor, it wheels about a point on the horizon rather
	340	than overhead.
`59c12827` 2026-09-28 Pavel Safronov	341	- The caps have more than one name. The sun cap is the end the beam enters by.
`42b4554e` 2026-09-29 Pavel Safronov	342	The far cap is also the star cap: it is the one with the stars in it — and the
	343	night cap, since night starts there: the sun goes out at it at dusk, and the moon sets
	344	out from it (D-088). All are used, and more names are added as they come into use (author,
	345	2026-09-27, 2026-09-28).
`769726ea` 2026-09-08 Pavel Safronov	346	- The far cap is glazed whole — a 100 km window looking into deep anti-sun
	347	space, not a wall with windows at its foot (D-045). Its structure survives as the
`c954a775` 2026-09-28 Pavel Safronov	348	window's mullions, a lattice of identical equilateral triangles 8.3 km on a side
	349	(D-078) — the old checker's pitch — so the one object in the world with a known scale still is one:
`769726ea` 2026-09-08 Pavel Safronov	350	the rule now reads against the sky instead of against a plate. The sun cap
`9c891d2e` 2026-09-08 Pavel Safronov	351	faces the collector rather than the sun, and is glazed too (D-050): §1.3.0
	352	retires the "heavy glare management" this section used to demand of it, because no
	353	direct sunlight has ever reached it. Through it, a 244 km black disc, stars round
	354	the edge of it, and the beam blazing out of the aperture at its centre.
`769726ea` 2026-09-08 Pavel Safronov	355	- By day the window is simply blue. §1.5 puts the far cap 100–200 km into the
	356	haze, so from anywhere but the deepward end the airlight in front of it swamps
	357	whatever is behind, and the cap reads as a disc of sky. The stars are there at
	358	noon and unseeable, which is a fact about eyes and not about the glass.
`9f91e995` 2026-09-29 Pavel Safronov	359	- The far cap is single-glazed, and it frosts (D-090). The glass is the coldest
	360	surface in the world and collects frost on its inner face, so Tower clears it one pane
	361	at a time, one pane per turn of the world in an order reshuffled every 35.1-hour loop.
	362	Close to, the window is a white lattice with a scatter of clear, black, starry
	363	triangles, and which ones are clear keeps changing. §1.9.6 has the numbers, and the
	364	cold wind and ice the window makes at its foot.
	365	- The sun cap is double-glazed (author, 2026-09-29; D-090). Its inner pane stays
	366	near the air's temperature, so it neither frosts nor chills the world: the Sunward Sea is
	367	a temperate sea and the Deepward Sea the only cold one. The two caps are glazed
	368	differently on purpose.
`da6bcb0e` 2026-09-08 Pavel Safronov	369	- The beam does not go through it. §1.3.3 puts the surviving quarter of the
	370	beam on a 3.2 km bullseye at the centre of the cap, and that bullseye is a mirror
	371	rather than glass: it returns the residual up the column for a second pass. The
	372	window is everything else, which is 99.9% of the disc.
	373	- The mirror is not the pinwheel's centre, and it is worth being clear why. The
	374	sky turns about the direction parallel to the spin axis, and from anywhere on
	375	the floor that direction is horizontal — so **the pinwheel's centre is at eye
	376	level, dead ahead**, down where the window meets the ground, not overhead and not
	377	at the middle of the cap. The mirror is a physical object on the axis, which
	378	from 270 km sits about 10° above that. They coincide only for an observer
	379	standing on the axis itself, and nobody can. By day the mirror blazes — it is
	380	returning 1.7 MW/m² — and is the brightest thing in Tower's sky; at night it
	381	banks with the beam and goes dark.
`866c7f96` 2026-09-07 Pavel Safronov	382
	383	Nobody aboard can ever see Earth. Tower holds a terminator orbit (D-004), which
	384	puts Earth roughly 90° off the axis — out the side of the cylinder, which is now
	385	solid hull. A habitat in Earth orbit whose inhabitants have never seen the planet
	386	they orbit.
	387
`99a2821b` 2026-09-29 Pavel Safronov	388	Spacecraft dock anywhere on the outer shell (author, 2026-09-28; D-087). There is no
	389	port: a ship matches the hull's spin and sets down where it likes. Docked, it turns with the
	390	hull at 700 m/s and hangs from its clamps, pressed outward at 1.02 g — its feet toward the
	391	hull and its floor toward space.
	392
`866c7f96` 2026-09-07 Pavel Safronov	393	The caps are therefore the only places in the world with a horizon that is not
	394	Tower. Whatever grows up around them, it will not be ordinary.
	395
	396	### 1.5 Atmosphere and the look of the sky
	397
	398	Air co-rotates with the shell. Because g falls linearly to zero at the axis, the
	399	atmosphere is much deeper than Earth's:
	400
	401	- Pressure at the axis, 50 km up: 5.2 kPa — thin, but genuinely air.
	402	- A vertical column floor-to-axis is ~10,600 kg/m², about one Earth atmosphere.
	403
	404	So the interior sky behaves like this, and the shader must reproduce it:
	405
	406	- Straight up you look through ~1 atmosphere and see the far side of the world
	407	100 km away — visible, but washed to pale blue like a very distant mountain range.
	408	- Along the axis you look through many atmospheres. The far end cap is not
	409	visible as a wall; it dissolves into blue haze around 100–200 km out. The world
	410	reads as endless in the axial direction and closed in the circumferential one.
	411	- The ground curves up on both sides into that same blue, meeting overhead.
	412	- The beam is a self-luminous scattering shaft 3.65° wide at 779 W/m²/sr —
`f16f084e` 2026-09-28 Pavel Safronov	413	render it as a bright sunlit cloud, not as a light source with a halo. It runs
	414	from cap to cap at every hour; by day it is dimmer past the sun (§1.3.1, D-079).
`59c12827` 2026-09-28 Pavel Safronov	415	- The sun is the other thing in the sky that is not land: a blazing disc on the
	416	beam, 3.65° across from directly beneath and smaller from afar, with glare round it
`42b4554e` 2026-09-29 Pavel Safronov	417	(§1.3.4). By night there is the moon instead, smaller in light and crossing the other
	418	way, as lit as Earth's Moon (§1.3.5). With the hull sealed, the rod, the sun and the moon are
	419	all there is.
`866c7f96` 2026-09-07 Pavel Safronov	420
	421	### 1.6 Orbit and attitude
	422
	423	- Tower holds a high circular orbit with its **orbital plane kept normal to the
	424	Earth–Sun line** — a terminator orbit. This is why one cap can face the sun
	425	permanently and Tower is never eclipsed.
	426	- The plane precesses 360° per year to track the sun. Tower's angular momentum is
	427	enormous, so this 1°/day reorientation is actively driven, continuously, forever.
	428	Canon treats this as Tower's defining maintenance burden.
	429	- Consequence for the interior view: the star field slowly drifts across the year
`e331ec2a` 2026-09-28 Pavel Safronov	430	while spinning fast every 7.5 minutes. Two nested motions. Both are drawn (D-075):
	431	the far cap looks at the antisolar point, which walks the ecliptic a degree a day.
`866c7f96` 2026-09-07 Pavel Safronov	432
	433	### 1.7 Coordinates
	434
	435	The canonical surface coordinate is (θ, z):
	436
	437	- `θ` — angle around the cylinder, 0 to 2π. θ = 0 is the centre of land strip 0.
	438	- `z` — distance from the sun cap, 0 to 540 km.
	439
	440	The 2D map is the direct unroll: `x = z`, `y = (θ − θ₀) · R`. No projection
	441	distortion — a cylinder unrolls exactly. This is a genuine advantage over mapping a
	442	globe and the map view should lean on it.
	443
	444	The map shows the surface once, bounded, so its extent is readable. That means
	445	it needs an edge, and the edge is placed at θ₀ = the centre of the last slat.
	446	Land strip 0 is centred on θ = 0, so cutting there would slice a whole strip in
	447	half across the top and bottom margins; cutting at a slat centre leaves every land
	448	strip whole and splits only a band of stars, which carries no geography. Same
	449	reasoning as putting Earth's map edge at the antimeridian. A sightline whose short
	450	route crosses the edge is drawn as two segments, so the drawn path always matches
	451	the measured distance.
	452
	453	---
	454
	455	### 1.8 Sightlines: Tower has two horizons
	456
	457	Along the axis the floor is perfectly flat and never falls away, so nothing is ever
	458	hidden by curvature. Tower's horizon is haze. Circumferentially the floor curves
	459	up, so distant land rises into the sky rather than sinking below a line. The two
	460	directions behave completely differently, and this is one of the most alien facts
	461	about living there.
	462
	463	Rayleigh transmission from a floor-level observer:
	464
	465	\| Distance \| Along the axis \| Across the interior (overhead) \|
	466	\|---\|---\|---\|
	467	\| 26 km \| 78 % \| 77 % \|
	468	\| 50 km \| 56 % \| 70 % \|
	469	\| 100 km \| 31 % \| 78 % \|
	470	\| 270 km (far cap from midpoint) \| 4 % — a ghost \| — \|
	471
	472	Two consequences:
	473
	474	- The axial horizon closes at 100–150 km. From the midpoint you cannot see
	475	either end cap. Everyone can see 100 km, knows there is more beyond, and cannot
	476	resolve it — a different psychology of distance than Earth's 5 km cliff-edge.
	477	- The far side of the world is clearer than the ground at the same distance,
	478	because a sightline across the interior rises through thin axis air while one
	479	along the floor grinds through full density. It gets better with distance: the
	480	land directly overhead, 100 km away, is the crispest far object in Tower at 78 %.
	481	Distant geography is best seen by looking up. People would orient by what is
	482	overhead; the ground is the vague part. This inverts the human default.
	483
	484	### 1.9 Water
	485
	486	Tower's hydrology is stranger than its geometry, and most of it follows from one
	487	fact and one absence.
	488
	489	#### 1.9.1 Coriolis never pushes surface water sideways
	490
	491	The floor's tangent plane is spanned by θ̂ and ẑ, and the spin axis is ẑ. For any
	492	flow along the surface:
	493
	494	- along the axis — `ẑ × ẑ = 0`, no Coriolis force at all;
	495	- around the circumference — `ẑ × θ̂ = −ŝ`, the force is purely radial.
	496
	497	The Coriolis term never has a component inside the surface. So **Tower's rivers
	498	do not curve.** No hemispheres, no Baer's law, no preferred bank erosion, no gyres,
	499	no cyclones. Every large-scale rotational habit of Earth's water and weather is
	500	absent, and a meander in Tower is pure flow dynamics with no thumb on the scale.
	501
	502	#### 1.9.2 What it does instead: everything vertical leans
	503
	504	The force goes into the floor rather than across it, so it appears whenever water
	505	moves up or down. Deflection of a free fall goes as h^1.5:
	506
`28f9a6bc` 2026-09-07 Pavel Safronov	507	\| Fall \| Lands (retrograde) \| Lean of the path \| Lean at impact \|
	508	\|---\|---\|---\|---\|
	509	\| 100 m \| 4.2 m \| 2.4° \| 3.6° \|
	510	\| 500 m \| 47 m \| 5.4° \| 8.1° \|
	511	\| 1,000 m \| 133 m \| 7.6° \| 11.3° \|
	512	\| 2,000 m \| 377 m \| 10.7° \| 15.8° \|
	513
	514	Two different angles, and the interior view needs both. The path leans by where
	515	the water lands against how far it fell — the tilt of a waterfall's plume seen
	516	whole. The impact lean is the direction the water is actually moving when it
	517	arrives, which is what a streak of it is drawn at, and it is half again the other in
	518	tangent. `src/canon/motion.ts` computes both.
`866c7f96` 2026-09-07 Pavel Safronov	519
	520	Rain falls permanently slanted — a raindrop at terminal velocity sits at a fixed
	521	1.47° against the spin, ~51 m of drift over a 2 km fall, never varying, never
`28f9a6bc` 2026-09-07 Pavel Safronov	522	reversing. It is fixed because drag holds the fall speed constant, so unlike free
	523	fall the angle does not grow with the drop: rain leans the same 1.5° whatever the
	524	cloud. Set against a waterfall's 11°, **the waterfall is the compass and the rain is
	525	not**, which is the opposite of what §2.4 originally assumed (D-034). Rising things lean the opposite way: smoke drifts spinward, rain drifts
`866c7f96` 2026-09-07 Pavel Safronov	526	anti-spinward. Every plume and every shower in Tower tilts, and they tilt against
	527	each other.
	528
	529	The same applies to anything that descends, not just water — see §1.11 on what it
	530	does to skiing.
	531
	532	Horizontal flow changes weight rather than direction (Eötvös): +0.57 % for a
	533	2 m/s prograde river, negligible hydrologically. It only matters at speed — an
	534	express train at 100 m/s gains 29 %, and anything moving retrograde at the 700 m/s
	535	rim speed is stationary in space and therefore weightless.
	536
	537	#### 1.9.3 A perfect cylinder has no slope anywhere
	538
	539	Potential depends only on radius, so **the whole floor is a single equipotential
	540	surface.** Water on it has no preferred direction: a perfect Tower has no rivers at
	541	all, forever.
	542
	543	Every river in Tower exists because the floor was shaped. There are no
	544	tectonics and no uplift, so erosion is strictly one-way — a 3 km range wears flat in
	545	~30 Myr under a wet engineered climate, ~150 Myr under a dry one. Tower's rivers
	546	are steadily destroying its landscape and the highlands must be rebuilt to keep them
	547	running. This is D-004's theme again: Tower's rivers are plumbing it chose to
	548	install and has to keep re-installing.
	549
	550	Two corollaries:
	551
	552	- No river can circumnavigate. A closed loop has no net descent.
	553	- Lakes curve upward. Level means constant radius, so across a 30 km lake the
	554	far shore rides 2.3 km above your tangent plane — Earth would hide it 18 m
	555	below the horizon. You look up at the opposite beach, and water appears to
	556	climb away from you.
	557
	558	#### 1.9.4 There is no passive climate at all
	559
	560	Tower has no latitude — every point is equidistant from the light — and with the
`9f91e995` 2026-09-29 Pavel Safronov	561	hull sealed it has no windows in its walls either. A uniform hull radiates at 274 K
	562	everywhere, so left alone the world settles into a flat calm: no gradient, no wind, no
	563	evaporation, no rain, no rivers. The one exception is the far cap, whose window is
	564	a cold wall the size of the cap (§1.9.6, D-090); it makes a gradient at the deepward
	565	end whatever Tower does.
`866c7f96` 2026-09-07 Pavel Safronov	566
	567	So every weather system in Tower is deliberate. Tower makes climate the only way
	568	left to it — by aiming light. It warms where it wants convection and shades where it
`9f91e995` 2026-09-29 Pavel Safronov	569	wants condensation; the hull's loss is the sink. Every cloud, every
`866c7f96` 2026-09-07 Pavel Safronov	570	rainfall, every jet stream is something Tower is doing, continuously, on purpose.
	571
`9f91e995` 2026-09-29 Pavel Safronov	572	Tower also sets the sink (D-090). The loss through the hull cannot be passive:
	573	1 km of rock conducting the mean 320 W/m² would need a difference of some 100,000 K
	574	across it, so heat reaches the outer skin because Tower sends it there. It follows
	575	that Tower can send less of it from one place and more from another. **It can move
	576	about 5 TW** — a tenth of the beam — between regions this way: enough to hold the far
	577	end cold and a few projects besides, not enough to run the climate on. Light is still
	578	how Tower makes weather; heat rejection is how it keeps the books.
	579
`866c7f96` 2026-09-07 Pavel Safronov	580	This is D-009 arriving at its conclusion. The mirrorlet swarm was already Tower's
	581	body language; now it is also its lungs and its weather. There is no autonomic
	582	layer underneath. If Tower's attention ever lapses, the rain stops.
	583
	584	Costs, for scale against a 54.3 TW budget:
	585
	586	\| \| \| \|
	587	\|---\|---\|---\|
	588	\| Earth-like rainfall, 1,000 mm/yr \| 12.2 TW \| 22.4 % — Earth spends the same fraction \|
	589	\| Recirculating all runoff (1,792 m³/s) against 500 m \| 8.8 GW \| 0.016 % \|
`9f91e995` 2026-09-29 Pavel Safronov	590	\| The far cap window's loss to space (§1.9.6) \| 0.65–1.9 TW \| 1–4 % \|
`866c7f96` 2026-09-07 Pavel Safronov	591
	592	#### 1.9.5 Rivers are a closed, pumped circulation
	593
	594	With no natural cycle and no natural slope, a Tower river is a loop: a headwater
	595	reservoir, a shaped descent through the landscape, a lake at the bottom, and a lift
	596	back to the top. Source and sink are the same system.
	597
	598	Two ways to close the loop, and they give completely different rivers:
	599
	600	- The pump outfall. A river begins at a machine. Walk to the source of any
	601	river and find a wall of water coming out of a structure — not a spring, an
	602	outlet. Costs a rounding error (above).
	603	- The made cloud. Tower evaporates the lake with aimed light and condenses it
	604	over the highlands, so rain falls exactly where the river should start. No
	605	machinery: the swarm is the pump. Costs the 22.4 % above, and buys real weather
	606	with it.
	607
	608	Canon uses both — made weather for the world's general hydrology, pumps for
	609	watercourses Tower wants under precise control.
	610
	611	Two consequences of the sealed hull:
	612
	613	- A river can circle the world. The surface is one unbroken sheet, so a channel
	614	can run the full 314 km circumference and close on itself — a lazy river returning
	615	to its own source. Gravity cannot drive a closed loop, so it is pumped.
	616	- The water inventory is conserved and exactly known. Nothing evaporates to
	617	space. Tower knows how much water it has, to the litre, forever.
	618
	619	Lifting is also slightly cheaper than on Earth, since gravity falls off with height:
	620	1 % cheaper at 1 km, 5 % at 5 km, 25 % at 25 km.
	621
`9f91e995` 2026-09-29 Pavel Safronov	622	#### 1.9.6 The far end is cold, and Tower keeps it so
	623
	624	Worked out with the author, 2026-09-28; D-090.
	625
	626	The window is a radiator. Glass is opaque to thermal infrared, so the far cap's
	627	single glazing does not let the world's heat out as light — it absorbs it, and its outer
	628	face radiates it to space at 3 K. A pane 0.1–1 m thick loses 80–250 W/m², and over
	629	the cap's 7,854 km² that is 0.65–1.9 TW, 1–4 % of the beam. Air cooled against the
	630	glass is denser and slides down the cap, which on a cap means radially outward to the
	631	rim, and it spreads sunward over the Deepward Sea as a cold wind off the window,
	632	roughly 5–15 m/s. Nothing Tower does makes this; it is what a cold wall does. The ice at
	633	the foot of the cap is where the physics was going anyway.
	634
	635	Tower keeps that end of the world dim, and lets it freeze in bands. Sunward to cap:
	636
	637	\| z (km) \| Band \| By day \| By night \|
	638	\|---\|---\|---\|---\|
	639	\| 496–512 \| open water \| grey sea at about freezing, with sea smoke where the cold wind crosses it \| dark \|
	640	\| 512–525 \| pack ice \| floes made at the fast ice's edge, carried sunward by the wind, melting where they meet open water \| dark \|
`e18dad04` 2026-09-30 Pavel Safronov	641	\| 525–528.5 \| fast ice \| dusk — the rod's glow and nothing aimed \| night; the sun goes out overhead at dusk \|
	642	\| 528.5–540 \| the Cap Range \| ice mountains, 2–3 km high against the glass, a few crests bare rock \| the same, dark \|
	643	\| 540 \| the window \| white frost with a scatter of clear panes, its foot buried in ice \| stars through the clear panes \|
`9f91e995` 2026-09-29 Pavel Safronov	644
	645	- The dark is dusk by day, not darkness. The rod's own glow cannot be aimed away
	646	(§1.3.2) and runs on past the sun to the cap (D-079), so the fast ice gets tens of W/m²
	647	by day — a permanent overcast dusk — and real night only by night. The sun still goes
	648	all the way to the cap (§1.3.4), so once a day it goes out directly over the ice, and
	649	the moon sets out from the same place.
`e18dad04` 2026-09-30 Pavel Safronov	650	- Ice mountains stand against the window (D-093). Snow off the window wind and the
	651	meltwater of every cleared pane come down at the cap's foot and freeze there, so the ice
	652	is thickest against the glass. But grounded ice cannot stand much higher than a few
	653	hundred metres over a few kilometres — it spreads under its own weight until the stress
	654	at its bed is what the bed will take, about 150 kPa for cold ice frozen down — and on a
	655	420 m sea that is a kerb: 280 m against a 50 km window. So **Tower raised a range there
	656	for the ice to stand on, as it raised the Uplands (D-064): the Cap Range**, rock rising
	657	from the sea bed at 524 km to about 2,400 m at the cap, higher in some places round the
	658	ring than others. Ice mantles it from where the rock leaves the water, about 528.5 km, in a
	659	low front over the fast ice, thickening as an ice sheet does to 350 m on the heights, and
	660	it drapes the ridges rather than burying them level, so the range reads as mountains and
	661	its sharpest crests stand out as bare rock. Against the glass it stands **2 to 3 km up the
	662	window**, and the window's foot is buried in it. The sea no longer meets the cap: the
	663	fast ice ends against the range.
`9f91e995` 2026-09-29 Pavel Safronov	664	- The fast ice holds. The window wind pushes on it with about 1,500 N per metre of
`e18dad04` 2026-09-30 Pavel Safronov	665	shore; 3 m of ice frozen to the range's foot holds some 3 MN. Tower has no tides — its moon
`9f91e995` 2026-09-29 Pavel Safronov	666	is light (§1.3.5) — so the thing that breaks Earth's fast ice out is absent. Storm swell
	667	is the threat to it, and the Deepward Sea is on the weather plan.
	668	- The whole sea is ice-cold, not only the ice. With no Coriolis in the plane of the
	669	floor (§1.9.1), a 1 K difference in the water drives an exchange of about 0.45 m/s,
	670	cold out along the bottom and warm in over the top. That mixes the sea's 44 km to within
	671	about a kelvin, so the open water sits at freezing. It is a polar sea, grey and foggy,
	672	and its coast has fog where the land's air comes down onto it. **No sea in Tower can
	673	be frozen in one corner** — only whole or not at all.
	674	- The window's bill is paid by the air. If the sea paid the 0.65–1.9 TW, the open
	675	water would need daylight on it, 140–400 W/m². Instead the weather runs one overturning
	676	cell: warm air from the lit lands comes deepward aloft to the glass, cools, sinks, and
	677	goes back sunward along the surface as the window wind. The sea pays only what that
	678	wind takes from the open water, which is also how fast ice is made — so **Tower sets
	679	the ice edge by how hard it runs the cell**.
	680	- Tower turns the hull down under the sea (§1.9.4). If the floor went on drawing its
	681	share, the sea would be cooled from beneath and freeze on its bed first, and no light
	682	would keep any of it open. The far end takes about 2 TW of Tower's 5 TW of heat control.
	683
	684	The window frosts, and Tower clears it one pane at a time. Cold glass collects frost
	685	on its inner face — very roughly millimetres a day, enough to whiten a pane in days — so
	686	left alone the far cap would go white and the stars would go. Tower heats one pane at a
	687	time from its frame: melting a pane's frost is about 6 × 10¹² J, a few minutes at tens of
	688	GW, and the meltwater runs down the cap onto the ice.
	689
	690	- One pane per turn of the world, every 7 min 29 s. The window has 282 panes
	691	(216 whole triangles and 66 cut by the rim, D-078), so a loop takes 35.1 hours —
	692	not a whole number of days, so the clearing drifts against day and night.
	693	- Shuffled, and reshuffled every loop. A fixed order could be learned by anyone who
	694	watched long enough; a fresh one each loop cannot. Each loop's order is drawn from the
	695	world's seed and the loop's number, so which panes are clear at any moment can be
	696	worked out without the history, the same in the app and in the book.
	697	- A pane's gap between clearings runs from almost nothing to almost two loops, so the
	698	frost on it ranges from clean glass to thick white. The window reads as a white lattice
	699	with a scatter of black, starry triangles, perhaps one in ten; how long a pane stays
	700	clear rests on the frost rate, which is rough to a factor of ten.
	701
`e18dad04` 2026-09-30 Pavel Safronov	702	As drawn (D-091). The Deepward Sea's `ice` in the world file puts the bands where the
	703	table has them, and the water shader draws the pack as floes and leads and the fast ice as
	704	one cracked sheet. Tower's aimed light falls from the shore to about a third at the ice
	705	edge, a tenth at the fast ice and nothing on it, which leaves the fast ice the rod's
	706	twentieth by day; the views show that through the same 0.35 power the exposure gives the
	707	light dial, so the fast ice reads as dusk, not black. The frost closes a cleared pane as
	708	1 − e^(−age / 10 h), which leaves about one pane in ten nearly clear, and the pane being
	709	cleared thaws across its turn. Both views share the window, so the frost is the same from
	710	outside.
	711
`abc0aad0` 2026-10-01 Pavel Safronov	712	#### 1.9.7 Farms on their own days
	713
	714	Asked for by the author, 2026-09-30; D-095.
	715
	716	Tower gives each crop the day its plant wants. Any light on any field at any hour is
	717	what the swarm is for (§1.3.1), so a farm in Tower does not live by the sun. The author's
	718	first thought was full sunlight around the clock; the plants would not thank Tower for it.
	719	Most flowering plants measure the night to know when to flower, and some — tomatoes — are
	720	injured by light that never stops. So every field gets darkness, and its own length of day:
	721
	722	\| \| Day Tower gives it \| Why \|
	723	\|---\|---\|---\|
	724	\| rapeseed, flax, wheat \| 18 h \| long-day plants: they flower sooner and fuller under long days \|
	725	\| lavender, poppies, phacelia, tomatoes \| 16 h \| long-day; tomatoes are day-neutral but need about six hours of dark \|
	726	\| tulips, sunflowers, maize, lettuce \| 14 h \| day-neutral, or nearly \|
	727	\| buckwheat, potatoes \| 12 h \| short-day; potatoes set their tubers on short days \|
	728
	729	- A field's day starts at sunrise and is lit as at noon from first light to last, not
	730	by a sun climbing and setting. A long-day crop is lit on into the night; a short-day
	731	crop has its light taken away before the sun sets.
	732	- Tower cannot make a field dark by day. The rod's own glow cannot be aimed away
	733	(§1.3.2), so a short day ends in the far end's dusk, a twentieth of the light, and only
	734	the world's night is truly dark.
	735	- The fields show at night. For the first hours after sunset most of them are still lit
	736	as at noon — a patchwork blazing in a dark world — and they go out one crop at a time,
	737	the last of them six hours after sunset at the equinox.
	738	- They cost the world a little of its night. Lighting fields after dark means a beam
	739	not quite banked, and the rod glows with the beam. With 250 km² of fields, chosen by
	740	the author for this, about 220 GW goes to them just after sunset — 0.4% of the beam —
	741	which adds about 0.4 W/m² of the rod's glow everywhere, a moonlit night's worth, falling
	742	to nothing by six hours after sunset. At 1,000 km² it would be a permanent twilight.
	743	- Nine farms share the 250 km², spread round the world and down its length (D-096):
	744	two on the Uplands beside the Uplands Ring, four in clearings cut out of Greatwood — one
	745	of them the nearest fields to the Capital — and three on the open ground before the far
	746	end, one at the Axial Line's railhead. Each is about 28 km² (provisional names: Ringside,
	747	Far Ringside, Greatwood Clearing, Capital, Deepwood, Greatwood, Railhead, Far and Last
	748	Fields). Three-quarters of the fields are flowers in bloom — tulips red, yellow, pink and
	749	white, lavender, sunflowers, rapeseed, poppies, flax, phacelia, buckwheat — and the rest
	750	maize, potatoes, tomatoes, wheat and lettuce.
	751	- Farms grow; they are not drawn (D-097). Each farm is a seed and an area, and grows
	752	outward over the land a patch at a time, taking the nearest and luckiest ground at its
	753	edge and never water, sand, rock, a range or a slope too steep to plough — so it comes out
	754	ragged, with lobes and bays, and goes round a river rather than across it. Its edge runs
	755	along its fields' edges: a field is in the farm or not, whole.
	756	- Fields are irregular, the way old farmland is. The land is divided into blocks about
	757	1.5 km across, with farm tracks along their edges, and each block was taken in hand on its
	758	own terms: its fields run at its own angle, are its own size (220–440 m), and are drawn out
	759	long by its own stretch. Inside it the fields have straight edges meeting at odd angles,
	760	and a third of them are cut again into long strips. No line runs further than a block, and
	761	no two blocks agree.
	762
`866c7f96` 2026-09-07 Pavel Safronov	763	### 1.10 Slat orientation — RESOLVED: none
	764
	765	Axial strips versus rings was weighed at length (D-016) and answered by removing
	766	slats entirely (D-017). The comparison is kept in D-016 because it established what
	767	the choice cost, and because the reasoning — that slat layout sets the shape of
	768	Tower's countries, its climate map and its astronomy all at once — is what made
	769	"none" a real option rather than an absence.
	770
	771	### 1.11 The world as built
	772
`376f2ce6` 2026-09-16 Pavel Safronov	773	Authored geography lives in `content/world.json` — the source of truth — as
	774	features the browser generates the terrain from live (world-generation.md, D-062).
	775	Names are provisional. Tower is laid out in **belts
`866c7f96` 2026-09-07 Pavel Safronov	776	along the axis**, which is the natural grain of an engineered climate (§1.9.4):
	777
	778	\| z \| \| \|
	779	\|---\|---\|---\|
	780	\| 0–42 km \| The Sunward Sea \| ring ocean at the foot of the sun cap \|
`03607270` 2026-09-08 Pavel Safronov	781	\| 55–140 km \| the range \| Westwall, The Sisters, Snowcrown (4,300 m), Eastwall — the named high points of The Girdle, which rings the world at z 90 km (D-051) \|
`14d35b7d` 2026-09-16 Pavel Safronov	782	\| 105–150 km \| The Uplands \| ground Tower raised to about 1,000 m, ringing the world, so the rivers off the range can run down to The Narrows (D-064) \|
`51c39d8b` 2026-09-17 Pavel Safronov	783	\| 148–218 km \| The Dry Reach \| desert ringing the world, 22,000 km², 13% of the surface: mesas over dune fields, dry washes, and salt pans ringed by shorelines (D-069) \|
`866c7f96` 2026-09-07 Pavel Safronov	784	\| 176/190/203 km \| three ridges \| ringing, concentric — and The Narrows is the only breach in all three \|
`abc0aad0` 2026-10-01 Pavel Safronov	785	\| 129–470 km \| the farms \| nine farms of about 28 km², 250 km² in all, round the world: on the Uplands, in Greatwood's clearings, before the far end (§1.9.7, D-095, D-096) \|
`00ceeedb` 2026-09-27 Pavel Safronov	786	\| 214–430 km \| Greatwood \| forest belt: about three billion trees, with meadows Tower left open in it (D-071) \|
`866c7f96` 2026-09-07 Pavel Safronov	787	\| 248–402 km \| The Deep \| 154 × 32 km sea, long down the axis and narrow around \|
`51c39d8b` 2026-09-17 Pavel Safronov	788	\| 270 km \| The Capital / The Spindle \| axial midpoint; 20 km across, its spinward edge on The Deep's shore (D-070) \|
`e18dad04` 2026-09-30 Pavel Safronov	789	\| 496–540 km \| The Deepward Sea \| ring ocean at the foot of the far cap: open water to 512 km, pack ice to 525, dim fast ice to the Cap Range (§1.9.6, D-090) \|
	790	\| 528.5–540 km \| The Cap Range \| ice mountains Tower raised against the far cap's window, 2–3 km high (D-093) \|
`99a2821b` 2026-09-29 Pavel Safronov	791	\| 110–480 km \| The Axial Line \| railway down the length of the world, through The Narrows (D-086) \|
	792	\| 140 km \| The Uplands Ring \| railway round the world across the Uplands (D-086) \|
	793
	794	The railways keep a grade of their own over the ground rather than cutting it, so they run
	795	on piers much of the way: 10–20 m up over ordinary country, and on long viaducts over the
	796	rivers' gorges. A train going round the world has a handedness, like a ski run: the
	797	Ring's trains, at 100 m/s, are 31% heavier running spinward and 27% lighter running
	798	antispinward (`canon/motion.ts`); a train along the axis feels nothing.
`866c7f96` 2026-09-07 Pavel Safronov	799
`a088e5d5` 2026-09-17 Pavel Safronov	800	Both ring seas carry ninety sailing ships each, and Tower's published weather plan
	801	(D-067) runs a 28-day cycle of storms, gales and a calm over them and The Deep.
	802
`51c39d8b` 2026-09-17 Pavel Safronov	803	#### What the desert is made of
	804
	805	The Dry Reach is not sand with some rock in it; it is the whole grammar of a desert,
	806	because Tower had seen deserts (D-069). Tiers of rock stand over dune fields whose crests
	807	run across the wind Tower sends there; rocky hills break up the open ground; a network of
	808	dry washes is routed by the same drainage the ranges are eroded by, because a channel
	809	network that ignores drainage is the one thing that would look wrong. In the lowest ground
	810	there are salt pans, dead flat, ringed by the shoreline benches of lakes that never
	811	stood. The middle of the Reach stands 150 m above its rim so that the washes have somewhere
	812	to run, and Tower keeps its rock 6.5 km clear of the rivers it had already routed — a mesa
	813	across The Narrows would leave the world's drainage in a slot.
	814
	815	Rock is laid in beds, and a bed in Tower is a constant radius, so the strata line up
	816	across separate mesas however far apart they stand. That is what makes a field of them read
	817	as one formation eroded out of one plateau.
	818
`866c7f96` 2026-09-07 Pavel Safronov	819	#### Why the desert rings
	820
	821	On a cylinder you cannot go around a band. Every desert on Earth can be
	822	circumnavigated; a ringed one cannot. It is an absolute barrier across the world's
	823	waist, and with the three ridges ringing too it becomes three concentric walls.
	824
	825	#### The drainage, and why it keeps the chokepoint
	826
	827	Four rivers come off the range — Westwall Water, Sisters Water, Eastwall Water and
	828	The Long Water. On Earth most drainages do not cut through a rising ridge; they
	829	are defeated and diverted, and only an antecedent river with enough power keeps
	830	its course. So three of the four are turned by First Ridge, run along its front
	831	gathering each other, and leave with the fourth through the single gap.
	832
	833	- The Narrows carries the entire world's runoff — ~392 m³/s off a 9,800 km²
	834	range, lifted 1,780 m for 6.9 GW (0.013% of budget).
	835	- The ridge-front reaches are the only circumferential water in Tower, and
	836	weigh fractionally more or less for it (§1.9.2). Everything else runs axially,
	837	where Coriolis is exactly zero.
	838	- Whoever holds The Narrows holds the axis of the world. The Capital sits behind it.
`80bcc97a` 2026-09-17 Pavel Safronov	839	- The Long Water falls twice (D-066): 680 m off the range below Hollow Tarn, into a
	840	gorge, and 170 m into The Deep at its mouth. Eastwall Water falls 440 m off its side of
	841	the range. Each leans antispinward as it drops.
`866c7f96` 2026-09-07 Pavel Safronov	842
`14d35b7d` 2026-09-16 Pavel Safronov	843	The drainage needed the floor raised, and generating it honestly is what showed it
	844	(D-063, D-064). As v1 authored it, the ground between the Girdle's foot and the Dry
	845	Reach — z 115 to 135 km — was a lowland barely 60 m high, below a plateau of
	846	800–1,100 m, and v1 painted its rivers across it a kilometre up. A river cannot climb.
	847	Generated faithfully, each needed an embankment up to 950 m high to reach The Narrows.
	848
	849	So Tower raised the lowland: The Uplands, a ring of ground lifted to about 1,000 m,
	850	meeting the Girdle's skirt on one side and the plateau's edge on the other. The rivers
	851	now fall steadily off the range, across the Uplands and onto the plateau, and the floor
	852	under them is mostly cut — The Narrows about 500 m deep — and built up by no more than
	853	~200 m anywhere, the height of a levee rather than a dam.
`376f2ce6` 2026-09-16 Pavel Safronov	854
`866c7f96` 2026-09-07 Pavel Safronov	855	#### The Deep is oriented for the view
	856
	857	Long down the axis and narrow around it, so you cross it the short way — around
`51c39d8b` 2026-09-17 Pavel Safronov	858	θ, where the floor curves up. The authored outline is 154 × 32 km and the water fills about
	859	18 km of that width; from the Capital's waterfront the far shore is that 18 km away and
	860	stands 2.6 km above eye level. Crossing it lengthwise instead would be dead flat. The
	861	orientation is the whole point.
	862
	863	The Capital is a footprint, not a dot (D-070). It is 20 km across, centred on the axial
	864	midpoint — the only centre a cylinder has — which is just wide enough that its spinward edge
	865	is on The Deep's shore, 9.8 km out, where the ground has come down from 300 m to the
	866	water's 120 m. So the city holds both the middle of the world and a waterfront. The streets
	867	and buildings inside that footprint are phase 7's.
`866c7f96` 2026-09-07 Pavel Safronov	868
	869	It is also the world's flywheel: 19× the diurnal heat storage of bare ground, and
	870	5.9 days at full power to move its temperature one kelvin. Tower still supplies
	871	every joule (§1.9.4), but the world now coasts for about a week rather than
	872	stopping the moment attention lapses.
	873
	874	#### The cap seas are not designed
	875
	876	Gravity on an end cap points radially outward — tangent to the cap. Nothing rests
	877	there; water runs down to the rim and pools. **Both ring oceans exist whether anyone
	878	planned them or not**, each with a 314 km shoreline and a 50 km cliff standing
	879	behind it. The only windows in the world are at their feet (§1.4).
	880
`9f91e995` 2026-09-29 Pavel Safronov	881	They are not the same sea. The far cap's window is a cold wall, so **the Deepward Sea is
	882	a polar one** — ice-cold throughout, and frozen in bands toward the cap (§1.9.6). The sun
	883	cap is double-glazed and does none of this, so the Sunward Sea stays temperate.
	884
`866c7f96` 2026-09-07 Pavel Safronov	885	#### Skiing, because it is a different sport here
	886
	887	Level motion feels no Coriolis (§1.9.1) but a descending skier has radial velocity,
	888	and that does deflect:
	889
	890	- Down the axis: a steady sideways push, always antispinward — 1.5% of g at
	891	15 m/s on a 20° slope, 6.4% at 35 m/s on 40°.
	892	- Around the cylinder: you get heavier or lighter. 8.6% at 30 m/s, 11.4% at 40.
	893
	894	So a retrograde run gets lighter the faster you go, which is self-reinforcing,
	895	while a prograde run grips harder as it accelerates. Every slope in Tower has a
	896	handedness. No Earth mountain does. Settlements sit at the tarns — Sisters Station,
	897	Hollow Station — around 2,100 m, with the runs above them.
	898
`e7a9f9dd` 2026-09-17 Pavel Safronov	899	The range as generated (D-065) is the named summits and a scatter of unnamed ones,
	900	joined by ridges and cut by water into branching valleys, all eroded as one group with
	901	the Girdle. The named summits are held at exactly their heights and are the highest
	902	ground around them; each tarn sits on a shelf the valleys were not allowed to cut, which
	903	puts Sisters Tarn at 2,173 m.
	904
`866c7f96` 2026-09-07 Pavel Safronov	905	#### Open questions
	906
	907	- The Spindle's height. 3.2 km is a placeholder; an object dropped from its top
	908	lands ~760 m antispinward of its base.
`abc0aad0` 2026-10-01 Pavel Safronov	909	- z 430–496 km is unauthored but for three of the farms (D-096). The circumference
	910	outside the named peaks is no
`03607270` 2026-09-08 Pavel Safronov	911	longer empty — The Girdle carries the range round the whole 314 km — but it is
	912	unwalked: peaks with no names, and no rivers drawn off them yet.
`866c7f96` 2026-09-07 Pavel Safronov	913
	914	## 2. Application architecture
	915
	916	### 2.1 Stack
	917
	918	- Vite + TypeScript (strict), no framework — the app is three canvases and
	919	a control panel, and a framework would not earn its weight.
`fc11b064` 2026-09-08 Pavel Safronov	920	- One layout breakpoint, at 720 px: above it the panel is a column beside the
	921	world, below it a drawer over it (D-043). The world is a full-bleed canvas in
	922	both, because all three views are drag-to-look and a scrolling page would be
	923	fighting them for every touch.
`866c7f96` 2026-09-07 Pavel Safronov	924	- Three.js for the exterior and interior 3D views.
	925	- Canvas 2D for the map view.
`376f2ce6` 2026-09-16 Pavel Safronov	926	- Web workers for world generation (world-generation.md §5): a pool of up to six,
`e18dad04` 2026-09-30 Pavel Safronov	927	driven through comlink. Each must answer a ping before it is given the world. One
	928	whose script fails, or that is still silent a few seconds after its siblings answered,
	929	is replaced at once, up to four tries, then dropped, so a dead worker costs a few
	930	seconds rather than freezing the load (D-080, D-092). Noise is simplex-noise, sampled in 3D on the
`376f2ce6` 2026-09-16 Pavel Safronov	931	cylinder itself so nothing tears at θ = 0. Those two are the only runtime
	932	dependencies besides Three.js.
`62458672` 2026-09-07 Pavel Safronov	933	- GitLab CI → GitLab Pages, publishing `dist/` as `static/`.
`866c7f96` 2026-09-07 Pavel Safronov	934
	935	### 2.2 Module layout
	936
	937	```
	938	src/
	939	canon/
	940	constants.ts single source of truth for every number in §1
	941	geometry.ts (θ,z) <-> 3D, slat layout, map <-> surface
`28f9a6bc` 2026-09-07 Pavel Safronov	942	atmosphere.ts the rotational density profile and its extinction (§1.5)
	943	motion.ts how things fall in the rotating frame (§1.9.2) — the only
`65484043` 2026-09-08 Pavel Safronov	944	evidence of the spin anywhere but the far cap window
`376f2ce6` 2026-09-16 Pavel Safronov	945	terrain/ world generation, pure TypeScript — runs in workers, on the
	946	main thread and under vitest alike (world-generation.md §5)
`e7a9f9dd` 2026-09-17 Pavel Safronov	947	compile.ts the world compile: shapes, river profiles, lake levels
	948	mountains.ts summits, ridge graphs, steady-state erosion, pinned summits
`51c39d8b` 2026-09-17 Pavel Safronov	949	grid.ts grids on the surface: drainage, blur, sampling — shared by the above
	950	desert.ts plateaus and mesas, dry washes, salt pans, abandoned shorelines
`00ceeedb` 2026-09-27 Pavel Safronov	951	forest.ts where trees stand, how big they are, and what a canopy is
`80bcc97a` 2026-09-17 Pavel Safronov	952	water.ts wind seas, fetch, river speed and foam: the water's physics
`a088e5d5` 2026-09-17 Pavel Safronov	953	sea-state.ts every lake and sea's waves and whitecaps now, from the weather
	954	ships.ts ship lanes, positions from the clock, the wave sum they ride
`99a2821b` 2026-09-29 Pavel Safronov	955	rails.ts railway lines, and the grade their track keeps over the ground
`80bcc97a` 2026-09-17 Pavel Safronov	956	falls.ts waterfall sheets, leaning antispinward as they fall
	957	cache.ts the compiled world kept in IndexedDB between visits
`376f2ce6` 2026-09-16 Pavel Safronov	958	field.ts the elevation function: one answer to "how high is it here"
	959	noise.ts seeded simplex noise on the cylinder, and the hash under it
	960	shapes.ts signed distance, smoothed lines, on the unrolled (z, θR) plane
	961	tile.ts the tile quadtree scheme, and one tile's mesh data
	962	palette.ts material weights to colour, as TypeScript and as GLSL
	963	map-image.ts the map's picture of the world, rendered in bands
	964	worker.ts one worker: compile, tiles, map rows
	965	service.ts the pool, generations, the status dialog's progress, ground queries
`866c7f96` 2026-09-07 Pavel Safronov	966	views/
`9d5a061c` 2026-09-27 Pavel Safronov	967	palette.ts one colour per feature kind, shared by the map and the list
`376f2ce6` 2026-09-16 Pavel Safronov	968	terrain-lod.ts the ground as a quadtree of tiles, refined around the eye
`99a2821b` 2026-09-29 Pavel Safronov	969	craft.ts the tour's flyers as meshes: paragliders to giant airships, trains, spacecraft
	970	tour-player.ts plays the tour's legs: the deal, the fades, the caption
`00ceeedb` 2026-09-27 Pavel Safronov	971	forest-view.ts the trees near the eye: meshes, then cards, then the canopy skin
`99a2821b` 2026-09-29 Pavel Safronov	972	tour/ the scenic tour, pure: no Three.js, flown by the views and the tests
	973	geo.ts the floor's coordinates and the tower's frame, and the sums between them
	974	director.ts a craft's track and bank, what is worth looking at, where the camera rides
	975	interior-legs.ts the legs inside, found in the compiled world
	976	exterior-legs.ts the legs outside, in kilometres, clear of the beam
	977	plan.ts the deal: every leg once, no two of a kind in a row, 12–18 s each
`866c7f96` 2026-09-07 Pavel Safronov	978	world/
`376f2ce6` 2026-09-16 Pavel Safronov	979	schema.ts world.json v2 types + validation: features, not places
`866c7f96` 2026-09-07 Pavel Safronov	980	instruments.ts sightline, viewshed, lighting probe, travel (§3.3)
`a088e5d5` 2026-09-17 Pavel Safronov	981	weather.ts Tower's weather plan read at an hour: what it does, what it told people
`3cc2b5bd` 2026-10-04 Pavel Safronov	982	photos.ts a saved shot of a 3D view: its numbers, checked (D-099)
`866c7f96` 2026-09-07 Pavel Safronov	983	state/
`9d5a061c` 2026-09-27 Pavel Safronov	984	store.ts selected point, time-of-day, spin phase, view mode
`866c7f96` 2026-09-07 Pavel Safronov	985	views/
`6bb061a6` 2026-09-14 Pavel Safronov	986	exterior.ts Three.js: hull, collector, beam, spin, point picker
`376f2ce6` 2026-09-16 Pavel Safronov	987	interior-model.ts ground tiles, caps, bore, beam and haze, shared by both 3D views
`866c7f96` 2026-09-07 Pavel Safronov	988	map.ts Canvas 2D: unrolled surface, slats, terminator, point picker
`3e898b51` 2026-09-28 Pavel Safronov	989	interior.ts Three.js: shell geometry, the haze shader of §1.5, beam
`866c7f96` 2026-09-07 Pavel Safronov	990	ui/
`9d5a061c` 2026-09-27 Pavel Safronov	991	app.ts the whole panel: list, detail card, weather board, readouts, view switching
`3e898b51` 2026-09-28 Pavel Safronov	992	eye-gauge.ts the interior's eye-height gauge and its landmarks of known height
`28f9a6bc` 2026-09-07 Pavel Safronov	993	scales.ts slider mappings — kept out of views/ so the panel can label
`3e898b51` 2026-09-28 Pavel Safronov	994	the eye-height gauge without pulling in Three.js
`9d5a061c` 2026-09-27 Pavel Safronov	995	main.ts loads world.json and starts the app
`3cc2b5bd` 2026-10-04 Pavel Safronov	996	vite.config.ts also makes world.json from content/world.json (§3.1), and on a dev
	997	server writes the author's saved shots to content/photos.json (D-099)
`6364748a` 2026-09-08 Pavel Safronov	998
	999	tools/ node-only, never bundled; plain .mjs with no build step
`376f2ce6` 2026-09-16 Pavel Safronov	1000	port-world.mjs the one-off port of v1's geography.json into world.json v2
`b4b8e46c` 2026-09-28 Pavel Safronov	1001	build-pages.sh the Pages site: every branch built into one, with branches.json (D-073)
`6364748a` 2026-09-08 Pavel Safronov	1002	screenshots.mjs drives the running application in a headless browser and
	1003	photographs it into docs/screenshots/ (D-042)
`3cc2b5bd` 2026-10-04 Pavel Safronov	1004	photos.mjs renders the shots in content/photos.json to photos/, the view alone,
	1005	at 4K (D-099)
	1006	browser.mjs what those two share: the browser, the warm world, waiting for terrain
`866c7f96` 2026-09-07 Pavel Safronov	1007	```
	1008
	1009	`canon/constants.ts` is the spine. Every derived figure — period, rim speed, land
	1010	area, slat width — is computed from radius, length, slat count and target land
	1011	area, never hard-coded. Changing the radius changes the whole app coherently.
	1012
	1013	### 2.3 State
	1014
	1015	One small observable store. Views subscribe; nothing owns anything else.
	1016
	1017	```ts
	1018	type TowerState = {
	1019	point: { theta: number; z: number } \| null // the picked location
	1020	tod: number // 0..1, position in the diffuser day cycle
	1021	brightness: number // W/m^2 mean, 30..320 -- the diffuser output setting
	1022	spinPhase: number // 0..2pi, rotation for star motion
	1023	spinning: boolean
	1024	view: 'exterior' \| 'map' \| 'interior'
	1025	probe: { from: SurfacePoint; to: SurfacePoint } \| null
	1026	}
	1027	```
	1028
	1029	The exterior and map pickers both write `point`; the interior view reads it. That
	1030	is the entire interaction loop.
	1031
`5f38efd0` 2026-09-07 Pavel Safronov	1032	### 2.4 The exterior view
	1033
	1034	Scene units are kilometres, so the code reads in canon numbers. Tower's axis lies
	1035	along world Z with the sun cap at z = 0, which puts a canon surface point at
	1036	`(R cos θ, R sin θ, z)` in the hull's own frame. The hull spins about Z and carries
	1037	that frame with it, so **picking resolves the ray hit back through
	1038	`worldToLocal`** — otherwise every point picked off a turning hull would be wrong by
	1039	the spin phase.
	1040
	1041	Two deliberate departures from physics, both reading aids of the same kind as the
	1042	map's hillshade:
	1043
	1044	- Fill lighting. Real sunlight here runs parallel to the axis, so Tower's flank
	1045	is edge-on to it and renders very nearly black — accurate and useless. Two fill
	1046	lights lift the hull enough to read its shape.
	1047	- A visible beam. In vacuum there is nothing between collector and cap to
`8b6287ba` 2026-09-07 Pavel Safronov	1048	scatter light, so the converging beam would not be visible at all. It is drawn
	1049	as rays because it is the thing the view is about.
`472390e2` 2026-09-09 Pavel Safronov	1050	- A dark collector. Both of its sides are dark, and for different reasons: the
	1051	face pointed at Tower is a 245 K radiator, and the face pointed at the sun is a
	1052	mirror, which shows the empty sky in front of it and not the sun behind the eye.
	1053	What makes it legible is the sunlit rim of D-054 — the same 4 km ring the sun cap
	1054	window sees from inside, drawn here as geometry rather than in a shader (D-055).
`6bb061a6` 2026-09-14 Pavel Safronov	1055	The mirror face is lit by the sun alone, in its own shader: as a standard
	1056	metal material it also reflected the fill lights, which do not exist, as a
	1057	blue-white sweep across the disc (D-060). The sun sits on the axis behind the
	1058	collector, so its glint shows only when looking nearly straight down that axis.
	1059
`e331ec2a` 2026-09-28 Pavel Safronov	1060	The stars are the interior's, and they are Earth's (D-075). The sky is a sphere
	1061	around the scene painted with the same star field the windows use (D-056), sampled by
	1062	direction from the camera so the stars sit at infinity and hold still as the camera
	1063	orbits. The field is the Yale Bright Star Catalogue — every star to magnitude 6.5 — set by
	1064	the clock's date: the axis points at the sun, so the sky behind Tower is fixed by the sun's
	1065	ecliptic longitude, and turns once a year. Outside, ecliptic north is up (scene +Y), the one
	1066	roll square to the axis on every day. Spin does not turn it — the camera is not riding the
	1067	hull — and there is no daylight to adapt to, so it is drawn at full gain (D-060).
`8b6287ba` 2026-09-07 Pavel Safronov	1068
`908833aa` 2026-09-28 Pavel Safronov	1069	The hull can be tried in other dress (D-076). Rock is the first: a cratered, lumpy
	1070	shell a few kilometres thick laid over the metal skin, never into it, with the windows
	1071	left clear. It is an experiment in how Tower might look, not canon — the mass alone would
`6368edcf` 2026-09-28 Pavel Safronov	1072	be a question for §1.2 — and it sits in the Hull switch beside True and X-ray. Piping
	1073	is the second (D-077): the skin plated in panels, banded every ~36 km with hoop pipes either
	1074	side, pipe bundles running between the bands on brackets, clustered blocks of plant, vents
	1075	whose grilles and plumes switch on and off at random, and thruster pods at each end that
	1076	fire rarely, with long flaring flames and real light on the hull. Everything is dusted,
	1077	matte where the dust lies, so the metal does not read as chrome. Every part is outside the skin, so the windows
`ab6ae94f` 2026-09-28 Pavel Safronov	1078	still see only Tower's inside. Rock and piping is the third (D-081), the two at once:
	1079	the reading is that rock was heaped over the plant as shielding, so it lies in banks tens
	1080	of kilometres across over about three fifths of the hull, half as tall again as the Rock
	1081	reading, with scarps at their edges; the plant
	1082	rooms and vents crowd into the bare ground between, the bands and pipe runs are laid
	1083	regardless and go under the rock, and the rock is dug clear round each thruster pod.
`908833aa` 2026-09-28 Pavel Safronov	1084
`8b6287ba` 2026-09-07 Pavel Safronov	1085	Everything in the scene is captioned — collector, beam, both caps — with screen-space
`472390e2` 2026-09-09 Pavel Safronov	1086	labels. A dark disc and a cone of light are not self-explanatory, and the collector
`8b6287ba` 2026-09-07 Pavel Safronov	1087	is the least intuitive object in Tower: it is larger than the world it feeds.
`5f38efd0` 2026-09-07 Pavel Safronov	1088
	1089	The default camera frames the whole system rather than Tower alone: the collector
	1090	is 244 km across and flies 320 km ahead, and it is the larger object.
	1091
`65484043` 2026-09-08 Pavel Safronov	1092	The hull has two readings, and the view switches between them (D-047). True
`6bb061a6` 2026-09-14 Pavel Safronov	1093	is the outer skin: bare structure, with a window at each cap.
`376f2ce6` 2026-09-16 Pavel Safronov	1094	X-ray wraps the map's picture of the terrain onto the outside instead — the same
	1095	image the map draws, rendered live from the world (world-generation.md §9) — from outside Tower is
`65484043` 2026-09-08 Pavel Safronov	1096	structure, so what that texture shows is what is inside, which makes it a diagram
	1097	and not a view. Both are worth having and they are not the same claim, so the
`aa201500` 2026-09-14 Pavel Safronov	1098	control is a two-way switch rather than a checkbox. True is the default, and the
	1099	last reading chosen is remembered across reloads and view switches (D-061).
`65484043` 2026-09-08 Pavel Safronov	1100
`6bb061a6` 2026-09-14 Pavel Safronov	1101	The inside of Tower is the interior view's own model (D-060), not a lookalike.
	1102	The displaced ground, both glazed caps, the far cap's bore and the beam are built
	1103	once in `interior-model.ts` and added to both scenes, so looking in through either
	1104	window from outside shows the same land, hazed by the same integral, as standing in
	1105	it does. Two things make that work from outside. The haze integral **clips its
	1106	segment to the air** — the part of the sightline inside the tube, between the sun
	1107	cap and the far cap's glass — so the kilometres of vacuum between the camera and the
	1108	window add nothing; from inside the clip is the whole segment and nothing changes.
	1109	And the windows are see-through: a pane that paints the computed sky from inside
	1110	is transparent from outside, carrying only the haze in front of it, so what shows
	1111	through is the scene that is really there — the land beyond the near cap, and the
	1112	collector and the stars beyond the far one. The shaders work in the tower's frame,
	1113	and the exterior hands them the world-to-tower transform each frame, because the
	1114	hull is turning and the air turns with it.
	1115
`14d35b7d` 2026-09-16 Pavel Safronov	1116	The outer skin keeps its own mesh and its own two modes. It sits **a kilometre out from
	1117	the floor**, where D-044 puts the wall's outer face, with a ring closing the wall at each
	1118	end — generated ground goes below the datum, and a skin at the floor's own radius let
	1119	sea floors and tile skirts show through the hull (D-064). Three's cylinder runs u
`376f2ce6` 2026-09-16 Pavel Safronov	1120	around and v along, while the image is the other way round, so the UVs are rewritten
`6bb061a6` 2026-09-14 Pavel Safronov	1121	from the original attribute rather than derived from vertex positions — the seam
	1122	vertices are duplicated, and deriving an angle from them smears one column of
	1123	triangles across the whole image.
`11a13dbf` 2026-09-07 Pavel Safronov	1124
`15d933c9` 2026-09-07 Pavel Safronov	1125	The camera position persists across reloads, alongside the active view, so
`6bb061a6` 2026-09-14 Pavel Safronov	1126	returning to the page returns to the vantage you left.
`15d933c9` 2026-09-07 Pavel Safronov	1127
`99a2821b` 2026-09-29 Pavel Safronov	1128	The scenic tour runs outside too (D-085): spacecraft, a new one every 12–18 seconds —
	1129	skimming the hull, circling it against its spin, docking on it, looking in through the far
	1130	cap, over the collector's rim, down the beam, and Tower, the collector and the sun framed
	1131	together. A leg flies either in space, where the hull turns past at real speed, or in the
	1132	hull's own frame, where it holds still and the stars wheel. No craft enters the beam's cone.
	1133
`6bb061a6` 2026-09-14 Pavel Safronov	1134	There are no place markers (D-060). Selecting a place still swings the camera
	1135	round to it, and a cap is framed from about 40° off the axis so its window faces the
	1136	camera; the sidebar and the map carry the places themselves.
`11a13dbf` 2026-09-07 Pavel Safronov	1137
`28f9a6bc` 2026-09-07 Pavel Safronov	1138	### 2.4 The interior view — built
	1139
`376f2ce6` 2026-09-16 Pavel Safronov	1140	Scope, since D-062: real geometry, and ground generated to match it.
`28f9a6bc` 2026-09-07 Pavel Safronov	1141
`376f2ce6` 2026-09-16 Pavel Safronov	1142	Real: the ground is the actual cylinder, curving up on both sides and closing
	1143	overhead, built from generated tiles (world-generation.md §6).
`65484043` 2026-09-08 Pavel Safronov	1144	Stars only through the far cap — the wall is sealed (§1.4), so for 539 of the
`e331ec2a` 2026-09-28 Pavel Safronov	1145	540 km the sky is land and light. The far cap is glazed (D-045) and the sky beyond it is
	1146	the real one (D-075): the Yale Bright Star Catalogue, baked into cells on a cube's faces
	1147	so a pixel reads only the nine cells round it, and looked up by view direction turned
	1148	about the spin axis by the spin phase — one turn every 7 min 29 s, the point on the axis
	1149	genuinely motionless — and then by the date, which sets where the antisolar point is.
`28f9a6bc` 2026-09-07 Pavel Safronov	1150
`376f2ce6` 2026-09-16 Pavel Safronov	1151	The ground is a quadtree of tiles, each a 65-vertex grid bent onto the cylinder
	1152	in a worker: 34 km tiles on the far side of the world, 33 m tiles underfoot, so vertices
	1153	are half a kilometre apart overhead and half a metre apart at your feet. A tile splits
	1154	once the eye is within 1.8 tile-widths of it, and only once all four of its children
	1155	have arrived — detail pops in, and the ground is never missing. The tiles carry
	1156	material weights rather than colour, and the shader turns them into colour from the
	1157	same palette the map uses, with v1's mottling and a little grain near the eye. There
	1158	is still no scenery: no buildings, no trees, no water surface of its own. Those are
	1159	phases 3–7 of world-generation.md.
`28f9a6bc` 2026-09-07 Pavel Safronov	1160
	1161	Haze is the shader, and it is integrated rather than faked. Every fragment
	1162	samples the rotational density profile 24 times along the ray to the camera and
	1163	extinguishes per channel — red survives twice as far as green, blue half as far,
	1164	which is what makes distance blue rather than grey. From the floor it reproduces
	1165	§1.8 from the inside: 78% straight up against 31% for the same 100 km along the
	1166	ground, printed in the readout so the claim can be checked rather than believed.
	1167	The airlight the haze adds is neutral; tinting it blue double-counts the
	1168	wavelength dependence and turns even the desert mauve (D-034).
	1169
`65484043` 2026-09-08 Pavel Safronov	1170	Nothing inside the scene rotates, because the observer, the ground and the air
`e27aaf20` 2026-09-08 Pavel Safronov	1171	all co-rotate. What falls carries the spin, and §1.9.2 is lopsided about how: rain
	1172	leans a fixed 1.5° whatever the cloud, because drag pins its speed, while only free
	1173	fall keeps accelerating and so keeps leaning. **The waterfall is the compass; the
	1174	rain is barely a hint.** Rain is no longer drawn (D-049) — 1.5° is not a picture,
	1175	and the pinwheel below does the job it was standing in for. The physics stays in
	1176	`canon/motion.ts` and stays tested; it was only ever the rendering that could not
	1177	carry it.
`65484043` 2026-09-08 Pavel Safronov	1178
`9c891d2e` 2026-09-08 Pavel Safronov	1179	The one thing that does turn is outside. The sky through the caps does not
`65484043` 2026-09-08 Pavel Safronov	1180	co-rotate, so it wheels once every 7 min 29 s about the motionless star on the axis
`3e898b51` 2026-09-28 Pavel Safronov	1181	(D-045). It is the only evidence of the spin in the view. Both caps are windows
`9c891d2e` 2026-09-08 Pavel Safronov	1182	(D-050), so it can be had looking either way along the axis — deepward into empty
	1183	space, or sunward past the black disc of the collector.
`28f9a6bc` 2026-09-07 Pavel Safronov	1184
`376f2ce6` 2026-09-16 Pavel Safronov	1185	The observer stands on the terrain by asking the same elevation function the tiles are
	1186	built from, at full detail. D-035's readback of a raster is gone with the raster.
	1187
	1188	Keyboard flight: W A S D or the arrows move along the heading, E and Q climb and
	1189	descend, shift is five times faster. Speed is proportional to height above the ground,
	1190	so the ground passes at the same apparent pace from a metre up or ten kilometres.
`28f9a6bc` 2026-09-07 Pavel Safronov	1191
`3e898b51` 2026-09-28 Pavel Safronov	1192	Instruments in the view: eye height from 1.7 m to the edge of the beam, 48.4 km up (D-084), with the local gravity
	1193	beside it — a vertical gauge up the view's right side, marked with real-world things of
	1194	known height so the number means something (D-082) — the five canon illumination settings of §1.3, a field of view fixed at 60° (D-083), and captions on every place still visible through the haze.
`28f9a6bc` 2026-09-07 Pavel Safronov	1195	Selecting a place walks the observer to it (D-038) — the haze horizon closes at
	1196	100–150 km, so turning to face something usually just points at haze.
	1197
`c954a775` 2026-09-28 Pavel Safronov	1198	Both caps are glazed (D-045, D-050), framed by a lattice of identical equilateral
	1199	triangles 8.3 km on a side (D-078), with a vertex on the axis where six meet. That is the
	1200	pitch of the polar checker it replaced (D-041), so it is still the only object in the world
	1201	with a known size and still doubles as a scale for judging distance, read against sky.
`6bb061a6` 2026-09-14 Pavel Safronov	1202	The exterior draws these same caps — the same meshes and shaders, not a copy of
	1203	them (D-060).
`65484043` 2026-09-08 Pavel Safronov	1204
	1205	The far cap's glazing is set a kilometre into its own frame, so from inside there is
	1206	a 1 km reveal around it. That is the only place the wall depth of D-044 can be
	1207	seen from within the world, which is why it is the only place it is drawn.
`28f9a6bc` 2026-09-07 Pavel Safronov	1208
`80bcc97a` 2026-09-17 Pavel Safronov	1209	Water is geometry (D-066). Every lake, sea and river is a surface at its own level
	1210	— a level in Tower is a constant radius, so a lake curves up with the floor — drawn over
	1211	the ground with the depth test finding the shoreline, and the ground under it drawn as
	1212	bed. Deep water is dark and shallow water shows the bed through it. Waves are sized from
`a088e5d5` 2026-09-17 Pavel Safronov	1213	each body's wind — Tower's weather plan, or the body's usual wind when nothing is
	1214	scheduled (D-067) — and the fetch it blows over, by the relations fitted to real seas, and
	1215	drawn as six components that displace the surface near the eye and shade it beyond;
`80bcc97a` 2026-09-17 Pavel Safronov	1216	rivers carry ripples downstream at the speed Manning's equation gives them, and turn
`a088e5d5` 2026-09-17 Pavel Safronov	1217	white on their rapids. Whitecaps cover the share of a sea the wind speed gives. Water
	1218	mirrors the hazed land overhead, and glints where it mirrors the beam.
	1219
`00ceeedb` 2026-09-27 Pavel Safronov	1220	The forest is trees (D-071). Greatwood is a density field — stems per hectare, thinned
	1221	at its edges, opened where Tower left meadows, stopped by water, rock and the treeline — and
	1222	the trees themselves are found by a rule rather than kept in a list, so the same trunks
	1223	stand in the same places for everyone who walks there. Within a few hundred metres they are
	1224	meshes; out to three quarters of a kilometre, cards turned to face the eye; beyond that the
	1225	tile carries a canopy skin at the canopy's own height, which sinks back onto the ground as
	1226	you approach. The Tall Wood is 52 km² of 90–115 m giants near the Capital, placed once
	1227	from the world's seed: a landmark standing 75 m proud of the wood around it.
	1228
`a088e5d5` 2026-09-17 Pavel Safronov	1229	Ships sail the ring seas (D-067): procedural hulls, mainsails and jibs, instanced, each
	1230	on a lane round the world at a position that is a function of the clock, riding the waves
	1231	drawn under it with the mainsail set to the wind. While a gale or storm is published for
	1232	their sea in time to get in, they are in harbour — off the water, since harbours are not
	1233	drawn yet; a squall announced too late catches them out.
	1234
`99a2821b` 2026-09-29 Pavel Safronov	1235	The scenic tour (D-085, replacing D-068's) flies the view itself, on the world's flyers:
	1236	a new one every 12–18 seconds, dealt at random, fading through black between them — a
	1237	paraglider on a summit's flank, a glider in a thermal, light aircraft and seaplanes, an
	1238	airliner round the Girdle, airships low down and giants near the axis, one of them circling
	1239	the sun outside the beam, trains on both railways, ships in fair weather and foul. Each
	1240	craft exists for its leg. The camera rides in it or chases it, banks with it, and is
	1241	pointed by a director at whatever is worth seeing from there — scored by the same haze
	1242	integral the view is drawn with, so it never turns to stare at something the air has eaten.
	1243	The legs are worked out from the world, so they follow its edits, and the screenshot tour
	1244	photographs them.
`80bcc97a` 2026-09-17 Pavel Safronov	1245
	1246	Waterfalls lean. A river's profile steps where it cannot slope — off a range, into
	1247	The Deep — and a step is a fall with a gorge below it. The falling sheet leaves the lip at
	1248	the river's speed and drifts antispinward by the free-fall drift of §1.9.2, so the
	1249	Long Water's 680 m fall off the range lands about 75 m antispinward of its lip. It is the
	1250	first thing in the view that shows the spin by leaning, which §1.9.2 always said the
	1251	waterfall would be.
	1252
	1253	The beam is drawn after all water: it is always in front of it, and drawn first it was
	1254	blended under the far side's seas.
`866c7f96` 2026-09-07 Pavel Safronov	1255
	1256	---
	1257
`9d5a061c` 2026-09-27 Pavel Safronov	1258	## 3. The world file, and how it changes
`866c7f96` 2026-09-07 Pavel Safronov	1259
	1260	The app is an instrument for writing the novel as much as a thing to look at. It
	1261	must answer questions like can the far face be seen from the midpoint?, *where
`9d5a061c` 2026-09-27 Pavel Safronov	1262	does a central embassy go?, can a lake overhang?* — and their answers are placed,
	1263	named and kept in the world file.
`866c7f96` 2026-09-07 Pavel Safronov	1264
`9d5a061c` 2026-09-27 Pavel Safronov	1265	### 3.1 One file, changed in the repository
`866c7f96` 2026-09-07 Pavel Safronov	1266
`9d5a061c` 2026-09-27 Pavel Safronov	1267	`content/world.json` is the world, and the only copy of it (D-072). The author
	1268	writes alongside Tower rather than in it, and changes the world by talking it over with
	1269	Claude, who edits the file; git keeps its history beside the prose. There is no editor
	1270	in the browser, no local draft in `localStorage`, and no import or export.
`866c7f96` 2026-09-07 Pavel Safronov	1271
`9d5a061c` 2026-09-27 Pavel Safronov	1272	\| \| \|
	1273	\|---\|---\|
	1274	\| World content \| `content/world.json`, committed; the app only reads it \|
	1275	\| What the app loads \| `world.json`, made from it by `vite.config.ts`: every `notes` emptied, every feature with `"public": false` left out \|
	1276	\| Instruments (§3.3) \| the sightline probe \|
	1277	\| Output \| permalinks to a point or place \|
	1278	\| Panel \| view controls, place list, a read-only detail card, the weather board \|
`866c7f96` 2026-09-07 Pavel Safronov	1279
`9d5a061c` 2026-09-27 Pavel Safronov	1280	The published `world.json` is derived, never committed: the dev server serves it
	1281	fresh on every request and reloads an open page when `content/world.json` is saved, and
	1282	the build writes it into `dist/`. There is no second copy to keep in step. There is
	1283	no backend — GitLab Pages is static — and none is needed: the loop is edit, commit,
	1284	push, and the published site serves it.
`a088e5d5` 2026-09-17 Pavel Safronov	1285
`9d5a061c` 2026-09-27 Pavel Safronov	1286	Everyone sees the same app. Until D-072 there was a writer mode (the default) and a
	1287	reader mode (`?reader=1`); the query parameter now does nothing.
`866c7f96` 2026-09-07 Pavel Safronov	1288
`3cc2b5bd` 2026-10-04 Pavel Safronov	1289	One exception, and it is not the world (D-099): on a dev server the author has a
	1290	button and a key that save the open view as a photograph, into `content/photos.json`,
	1291	written by the dev server. It is not in the build, so readers still see one app, and it
	1292	changes nothing about the world: a photograph is a camera position and a moment.
	1293
`866c7f96` 2026-09-07 Pavel Safronov	1294	### 3.2 The world file
	1295
	1296	```jsonc
	1297	{
`376f2ce6` 2026-09-16 Pavel Safronov	1298	"version": 2,
	1299	"seed": 1729, // every feature's randomness mixes this in
	1300	"ground": { "baseM": 60, "reliefM": 260, "notes": "" },
	1301	"features": [{
	1302	"id": "the-deep", // permalink target; see below
	1303	"name": "The Deep",
`99a2821b` 2026-09-29 Pavel Safronov	1304	"kind": "mountains\|lake\|sea\|river\|desert\|forest\|settlement\|road\|path\|railway\|embassy\|tower\|landmark\|note\|region",
`376f2ce6` 2026-09-16 Pavel Safronov	1305	"geometry": { "type": "polygon", "points": [[theta, z], ...] },
	1306	// or point, polyline, or band { "zFrom", "zTo" } for anything ringing the world
`866c7f96` 2026-09-07 Pavel Safronov	1307	"blurb": "public description, shown to readers",
	1308	"notes": "the author's working notes — NEVER shipped",
`376f2ce6` 2026-09-16 Pavel Safronov	1309	"public": true, // false = not ready to exist publicly
	1310	"seed": 1437950893, // written once at creation, never from the id
	1311	"levelM": 120, "depthM": 330, "basin": "flooded", "shoreM": 11000
	1312	// ...and whatever parameters the kind has: world-generation.md §3
`a088e5d5` 2026-09-17 Pavel Safronov	1313	}],
	1314	"weather": { // Tower's published plan (D-067)
	1315	"cycleDays": 28, // the plan repeats; 0 for never
	1316	"events": [{
	1317	"id": "deepward-sea-storm", "target": "deepward-sea", "kind": "calm\|breeze\|gale\|storm",
	1318	"start": { "day": 20, "hour": 18 }, "durationH": 30,
	1319	"wind": { "directionDeg": 60, "speedMS": 30 }, // toward; 0 deepward, 90 spinward
	1320	"publishedAt": { "day": 17, "hour": 9 },
	1321	"revisions": [{ "at": { "day": 21, "hour": 6 }, "kind": "gale",
	1322	"wind": { "directionDeg": 60, "speedMS": 18 }, "reason": "..." }]
	1323	}]
	1324	}
`866c7f96` 2026-09-07 Pavel Safronov	1325	}
	1326	```
	1327
`376f2ce6` 2026-09-16 Pavel Safronov	1328	Every kind has the same `geometry` field, so the map, the list and the editor treat
	1329	them one way; what a kind adds is parameters beside it, and a phase of
	1330	world-generation.md adds a parameter only when a generator reads it. v1 files, with
	1331	`places`, load as empty — there is no backwards compatibility (D-062).
	1332
`866c7f96` 2026-09-07 Pavel Safronov	1333	Two text fields, deliberately separate. `blurb` is written for readers and
`9d5a061c` 2026-09-27 Pavel Safronov	1334	ships; `notes` is the author's working thinking and never reaches the app. One field
	1335	with a flag would have made every note a publication accident waiting to happen.
`866c7f96` 2026-09-07 Pavel Safronov	1336
`9d5a061c` 2026-09-27 Pavel Safronov	1337	Ids are permalink targets. Once a place has been linked to, its id should not
	1338	change even if its name does; a river names what it flows into by id, so renaming an
	1339	id means rewriting those references too.
`866c7f96` 2026-09-07 Pavel Safronov	1340
	1341	Coordinates are canon (θ radians, z metres, §1.7) — never map pixels, so the file
	1342	survives any change to how the map is drawn.
	1343
	1344	The `public` flag is a privacy trap worth naming. Working notes ("embassy here?
`9d5a061c` 2026-09-27 Pavel Safronov	1345	check sightline to the cap") are kept out of the app, and a `"public": false` feature
	1346	is left out of it entirely. But **`content/world.json` is committed to a public
	1347	repository**, notes and unpublished features included — exactly as
	1348	`content/geography.json` was before it — so anything in it is public to anyone who
	1349	reads the source. The flag keeps things out of the map, not out of sight. Whether
	1350	private notes should live somewhere else — a private repo, or a second one — is the
	1351	author's call and is deliberately unresolved.
`376f2ce6` 2026-09-16 Pavel Safronov	1352
`866c7f96` 2026-09-07 Pavel Safronov	1353	### 3.3 Instruments
	1354
`9d5a061c` 2026-09-27 Pavel Safronov	1355	The measuring tools answer questions the novel actually raised. Only the sightline
	1356	probe is built; the rest are planned:
`866c7f96` 2026-09-07 Pavel Safronov	1357
	1358	- Sightline probe. Pick two points; get surface distance, straight-line
	1359	distance, optical depth, transmission, and a plain verdict (*crisp / hazy / ghost
`9d5a061c` 2026-09-27 Pavel Safronov	1360	/ invisible*). This is the tool that answered §1.8, and the single most
	1361	illustrative thing in the app.
`866c7f96` 2026-09-07 Pavel Safronov	1362	- Viewshed overlay. From a selected point, shade the whole map by transmission.
	1363	It renders the axis-versus-overhead asymmetry as one picture, which is worth more
	1364	than the table in §1.8.
	1365	- Lighting probe. At a point, illumination across the day cycle at the current
	1366	brightness setting (§1.3) — for writing a scene at a specific hour.
	1367	- Travel. Surface distance and journey time between points at chosen speeds,
	1368	including whether the route crosses a slat.
	1369	- Sky-at-a-time. Star field, beam position and Earth transits for a given point
	1370	and moment, so a described sky is a correct sky.
	1371
	1372	### 3.4 What readers get
	1373
	1374	The public link is the finished map: embassies, towns, lakes, named regions — the
	1375	permanent things, behaving like any map application. Plus the exterior view, the
	1376	interior view from any point, and permalinks so a reader can be handed a place and
`9d5a061c` 2026-09-27 Pavel Safronov	1377	a moment. Reading the world, not editing it — which, since D-072, is what the author
	1378	gets too.
`866c7f96` 2026-09-07 Pavel Safronov	1379
	1380	## 4. Phases
	1381
	1382	1. Design — this document and `decisions.md`. ← current
	1383	2. Scaffold — Vite/TS/Three, CI to Pages, `canon/` implemented and unit-tested.
`5f38efd0` 2026-09-07 Pavel Safronov	1384	3. Exterior — ✅ hull, caps, collector, beam, spin, and hull point picking.
`866c7f96` 2026-09-07 Pavel Safronov	1385	4. Map — unrolled surface, slat rendering, picking, sync with exterior.
`3e898b51` 2026-09-28 Pavel Safronov	1386	5. Interior — ✅ shell geometry, the haze shader, the beam, eye height,
`65484043` 2026-09-08 Pavel Safronov	1387	and the five illumination settings. Stars, but only through the far cap window.
`866c7f96` 2026-09-07 Pavel Safronov	1388	6. Writer mode — ✅ *built ahead of 3–5, at the author's request, because the
	1389	world needs developing before there is anything to render.* Map view, place
	1390	editing for all thirteen kinds, points/polylines/polygons, localStorage
	1391	autosave, backup and static exports, import, and the sightline probe.
`9d5a061c` 2026-09-27 Pavel Safronov	1392	*Removed by D-072: the world is now changed in `content/world.json`, and only
	1393	the sightline probe remains.*
	1394	7. Content pipeline and reader mode — ✅ reader and writer modes (D-011, one
	1395	mode since D-072);
`376f2ce6` 2026-09-16 Pavel Safronov	1396	permalinks (D-010). The terrain pipeline of D-019 — `content/geography.json` and
	1397	`npm run terrain` — is replaced by live generation (below).
`6364748a` 2026-09-08 Pavel Safronov	1398	8. Polish — mobile ✅ (the sidebar is a drawer below 720 px, D-043) and a
	1399	screenshot tour that photographs all ten views through the UI, D-042.
`fc11b064` 2026-09-08 Pavel Safronov	1400	Remaining: transitions, performance.
`866c7f96` 2026-09-07 Pavel Safronov	1401
`28f9a6bc` 2026-09-07 Pavel Safronov	1402	All five view phases are built. Phase 2's `canon/` landed with phase 6, since the
	1403	map could not be drawn without it.
`866c7f96` 2026-09-07 Pavel Safronov	1404
	1405	Shareable permalinks are implemented (phase 7) — the app has
	1406	readers, and "stand here and look at this" is the whole reason it exists as a
	1407	companion piece. Named locations from the novel should be markable on the map for
	1408	the same reason.
	1409
`376f2ce6` 2026-09-16 Pavel Safronov	1410	Live world generation — in progress, planned in world-generation.md (D-062).
	1411	Phase 1 ✅ (D-063): world file v2, the elevation function, the worker pool, tiled
`e7a9f9dd` 2026-09-17 Pavel Safronov	1412	ground, the status dialog, keyboard flight, the map drawn from the features. Phase 2 ✅
`80bcc97a` 2026-09-17 Pavel Safronov	1413	(D-065): mountain ranges of summits, ridges and eroded valleys, and summit editing. Phase 3
`a088e5d5` 2026-09-17 Pavel Safronov	1414	✅ (D-066): water as surfaces with waves and flow, and waterfalls that lean. Phase 4 ✅
`51c39d8b` 2026-09-17 Pavel Safronov	1415	(D-067): Tower's weather plan with revisions, a day on the clock, and ships. Phase 5 ✅
`00ceeedb` 2026-09-27 Pavel Safronov	1416	(D-069): the desert's mesas, dunes, washes, salt pans and shorelines. Phase 6 ✅ (D-071):
	1417	Greatwood as individual trees, its meadows, and the Tall Wood of giants. Phases 7–8 bring
	1418	settlements and roads — procedural scenery this section used to list as out of scope. Clouds and rain stay
`376f2ce6` 2026-09-16 Pavel Safronov	1419	undrawn (D-049).
`e331ec2a` 2026-09-28 Pavel Safronov	1420
	1421	## 5. Backlog
	1422
	1423	Things decided to be worth coming back to, not scheduled.
	1424
	1425	- The pinwheel's motionless star (author, 2026-09-27). §1.4 promises one motionless
	1426	star at the centre of the turning sky, and the real sky (D-075) has none there — the
	1427	antisolar point walks a degree a day. The placed star in `STAR_GLSL` is not canon
	1428	and stays only until this is revisited: a motionless point, a beacon Tower hangs there,
`908833aa` 2026-09-28 Pavel Safronov	1429	or nothing.
`f16f084e` 2026-09-28 Pavel Safronov	1430	- The sun's share of the beam (D-079). The rod now runs on past the sun at 70% of
	1431	itself, which says the shoal takes only 30% — but the ground is still lit as if the sun
	1432	took the whole beam. Canon has to settle the split, and the light budget with it.
`ab6ae94f` 2026-09-28 Pavel Safronov	1433	- The exterior's dress (D-076, D-077, D-081). Rock, Piping, and Rock and piping are
	1434	experiments, labelled as such in the Hull switch. Pick one or keep the bare skin — and
	1435	if a heavy one stays, answer for its mass. The combined dress gives the rock a reason
	1436	(shielding heaped on the plant), but taller and over three fifths of the hull it weighs
	1437	about what D-076's shell does, so the mass question stands.
`99a2821b` 2026-09-29 Pavel Safronov	1438	- Traffic (D-085). The tour's craft exist only for their legs: nothing flies, sails the
	1439	sky or runs the railways when the tour is not watching, except the ships. A world with
	1440	timetables — trains on the lines, airliners between the stations, giants on their slow
	1441	circuits — would be the honest next step, and would let a reader standing anywhere see
	1442	them go by.
	1443	- The Axial Line's 7% grade (D-086), where it comes down off the plateau into Greatwood,
	1444	is a rack railway's grade, not an adhesion one. Regrade it round the slope, or say it is a
	1445	rack section.
	1446	- The giant airships (D-087) are a consequence worked out from the thin air near the
	1447	axis, not canon. Whether Tower's sky has them is the author's call.
`42b4554e` 2026-09-29 Pavel Safronov	1448	- The moon's light (D-088). It is drawn as fed by Tower lifting the banked beam, so the rod
	1449	is the same either side of it; the sun instead takes its share from the rod and leaves it
	1450	dimmer past it (D-079). Canon could have the moon do the same, or settle why it does not.
`e18dad04` 2026-09-30 Pavel Safronov	1451	- The sun seen from the ice (D-091). Tower aims none of the sun's light at the fast
	1452	ice, so by §1.3.1's own rule the sun should look dim from there — a shoal lit toward
	1453	everyone else. It is drawn as bright as from anywhere. Whether the sun going out over the
	1454	ice each evening is seen from the ice as a blaze or as a dark disc in lit air is the
	1455	author's call.
`abc0aad0` 2026-10-01 Pavel Safronov	1456	- The farms' light at night (D-095). Lighting the fields after sunset keeps the beam
	1457	from being fully banked, and the rod's glow with it: about 0.4 W/m² more everywhere at
	1458	sunset, nothing by six hours after. The app's night light does not include it yet.
	1459	- 3D models for the things drawn from plain shapes (author, 2026-09-30). Everything that
	1460	moves or stands on the land is built in code from boxes, cones and spheres. The author will
	1461	supply real models; the app needs a way to load them. The list, with sizes as drawn:
	1462	- Tour craft (`views/craft.ts`, metres, nose along +x, top along +y): paraglider (wing
	1463	~10 m), glider (17 m span), light aircraft (11 m span), seaplane, helicopter (11 m rotor),
	1464	airliner (42 m), airship (120 m), giant airship (420 m), locomotive (22 m), railway
	1465	carriage (25 m), spacecraft (~80 m).
	1466	- Instanced, drawn by the hundred or thousand: the sailing ship as hull, mainsail and jib
	1467	(~180 of them, 8–45 m; the mainsail swings about the mast, so it must stay a separate
	1468	part with the mast at the origin), conifer, broadleaf and giant tree (up to 6,000 each,
	1469	`views/forest-view.ts`), and the flat tree cards for distant woods (up to 75,000 — an
	1470	image, not a model).
	1471	- Not candidates: terrain, water, ice, falls, the railway viaducts, the hull dressings, the
	1472	collector, beam, sun, moon and windows, all of which are shaped by the world.
	1473
	1474	The plan: glTF binary (`.glb`) files in a `models/` folder, a small manifest naming which
	1475	kind each replaces and how it faces, and the built-in shape as the fallback for any kind
	1476	without one, so models can arrive one at a time. Imported models go through Tower's own
	1477	lighting and haze — otherwise they are lit wrong and never fade into the distance — keeping
	1478	each part's colour at first, and image textures once a textured variant of the shader
	1479	exists. Budgets: tour craft can be detailed (tens of thousands of triangles); ships a few
	1480	thousand; trees a few hundred. Models must be licensed for redistribution, since the app is
	1481	published.