Satellites, end to end: CelesTrak element sets behind the same TTL cache
the weather and the flights use, served as TLEs rather than as positions,
and propagated in the browser with SGP4.
Sending elements is the same trick `flights/plan.ts` plays and it has a
better excuse here — a TLE *is* the closed form, valid for days either
side of its epoch, so one cacheable fetch every six hours replaces a poll
and every viewer agrees about where everything is.
Two things are worth knowing about the shape of it:
- There is no region parameter. An aeroplane at 10,000 m is local and
a satellite at 550 km is above the horizon for a circle two thousand
kilometres across, so one catalogue serves both boards and the client
decides what is above its own horizon. Only the observer is per-city,
which is why `main.ts` shares the elements and rebuilds the catalogue.
- The layer draws on a dome, because it cannot draw anywhere else.
`world.metres(550_000)` is 21,000 scene units against a far plane at
3,000. Azimuth and elevation are real; the radius carries nothing.
Off by default: a clone that started pulling CelesTrak on `npm run dev`
would have volunteered somebody else's bandwidth for its onboarding.
Godmode gets the two dials that point at the sky rather than at the
light — fabricated traffic, which composes with a live ADS-B feed instead
of replacing it, and a switch for the satellite layer with a count beside
it. Both are god-only lies about the inputs, in the manner of the weather
override.
`satellite.js` is the second runtime dependency this package has taken.
Its entry point star-exports an Emscripten build that cannot be shaken
out, so `noWasmPropagator` in the Vite config cuts it: 308 kB of WASM
loader for a bulk propagator nothing calls, against 26 kB for the SGP4
that does the work.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Six agents in parallel, and the two city packs independently reported the same
blocker: `focusRegions` and `coarseFactor` existed on the `City` type and
nothing implemented them. Uniform lattices would have been 2.9M points for
Southern California and 3.7M for the expanded bay. Both packs were unloadable
as written.
`buildAxis` is the answer, and it is honest about its limits: refinement is per
axis, not per rectangle, so a focus region sharpens its whole row *and* its
whole column. Two regions at opposite corners refine nearly everything between
them. Measured, not guessed — the bay went 0.53M points with one region and
1.64M with three, for detail nobody is looking at from a board this wide. One
region each, coarse factor ten, and the builds land at 3.8 s and 2.3 s.
Then three things that were only ever right because San Francisco was the only
city. `maxDistance: 340` and a 170-unit shadow box were constants tuned for a
230-unit board; the bay is 1003 units across and the camera physically could
not retreat far enough to frame it. Fog distances were scene units pinned to
the same assumption. And `minVisibilityM` defaulted to 4.5 km of honest
weather, which over ninety-four kilometres of bay correctly hides three
quarters of it — the night view was a black rectangle for a completely
reasonable reason. All three now derive from the board.
The moon is a real ephemeris and its light is a deliberate lie: 1.15, against a
physical ratio of one to four hundred thousand. What is being reproduced is
what a moonlit night looks like on a screen in a lit room.
The CI gate caught itself, which is the part worth keeping. Port 8431 was
already held by a server from an earlier session, so the boot check polled a
healthy stranger while the process it started died on EADDRINUSE. It now
refuses to run rather than pass.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
karti
Karti Tripathi