Turn every body in the system view by its IAU pole and prime meridian, so the lit face is the real one
Until now each body's axis was its orbit normal, tipped by the obliquity about the orbit's node, an azimuth the data never gave. Its phase started at an arbitrary point at the elements' epoch. The rate and the sense were real; the face towards the Sun was not. Now each of the 33 bodies with IAU elements is set, every tick, from its pole and its W at the clock's date. Eris, Haumea and Makemake keep the old fallback: their published period, about their orbit normal. None of them has an obliquity, so the tilt code that only served bodies now turned by the IAU is gone. Exoplanets have no rotation published and stay still, as before. The texture convention is settled once, in src/app/shared/rendering/body-orientation.ts (MAP_TO_BODY): - SphereGeometry runs u eastward about +Y from a seam on -X, so u = 0.5 faces +X. - Every photograph in the catalogue is centred on longitude 0 with east to the right. Checked on the maps: Greenwich; Olympus Mons 134 degrees left of centre; Mare Crisium right and Mare Orientale left; Kuiper just left. - A map labelled in west longitude is still drawn east-right, so where longitude 0 sits is the only question, and for all of them it is the centre. - So a quarter turn about X puts the map on the IAU body frame: pole +Z, prime meridian +X. The scene is already ICRF equatorial (the ecliptic is turned into it by the J2000 obliquity), so the pole goes in as it is. The equator frame is built through laplacePlaneToEquatorial, the same conversion the moons' Laplace planes use; moonFrame now calls it too. The clock is UTC and the elements TDB, so TT - UTC (69.184 s) is added: Earth turns 0.29 degrees in that time, Jupiter 0.70 and Phobos 0.90. Measured on the live app (port 4311), clock pinned to 2025-06-01 12:00 UTC: - The Sun stands over 0.433 W, 22.125 N on Earth's drawn sphere. The equation of time puts it at 0.53 W. - Each body was drawn one light-time earlier and compared with Horizons' observer quantities 14 and 15: - Earth (from the Sun): longitude 0.095 off. - Mars: sub-Earth 0.001, sub-solar 0.004. - Jupiter: sub-Earth 0.005, sub-solar 0.002. - The Moon: sub-solar 0.004; sub-Earth 0.699, which is the error of its mean orbit. - Horizons' latitudes are planetodetic. Raw, they differ by the flattening: Earth 0.14, Mars 0.23-0.27, Jupiter 0.33, the Moon (a sphere) 0.000. The unit tests put the same comparison through real raycasts on the drawn spheres' texture coordinates, with the latitudes put on each body's flattened figure. Every residual is within 0.09 degrees, but for the Moon's sub-Earth point (0.70 and 0.09). The retrograde tests of #33 are rewritten for the IAU's convention: a planet's named pole is the one on the north side, so W runs backwards for Venus and Uranus, while Pluto follows the right-hand rule. The spin read off the drawn sphere, against the drawn orbit's normal, is 177.36 for Venus, 97.77 for Uranus and 119.61 for Pluto, all past 90, and 23.44 for Earth. Each is within 0.5 of Horizons. Six mutants, each failing its named test: the map upside down; UTC taken for TDB (Jupiter's test); W turned the wrong way (the retrograde test, and again Earth's noon test); moons, or planets, not turned by the IAU; and the fallback ignoring a negative period. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Claude Opus 5.5
@@ -5,8 +5,9 @@ import { PlanetAppearance } from '../../shared/astro/planet-appearance';
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import { planetTexture } from '../../shared/rendering/procedural-planet-texture';
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import { bodyTexturePath, loadCachedTexture } from '../../shared/rendering/texture-catalog';
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import { isPropagatableOrbit, keplerRates, meanElementsAt, orbitEllipsePoints, positionAtEpoch, resolveGravitationalParameter, resolveOrbitalElements } from '../../shared/astro/kepler';
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import { CartesianCoordinates, laplacePlaneToEquatorial, OBLIQUITY_J2000_DEG } from '../../shared/astro/coordinates';
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import { BodyRecord, MeanElementRates, OrbitalElements } from '../../shared/models/body.model';
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import { CartesianCoordinates, OBLIQUITY_J2000_DEG } from '../../shared/astro/coordinates';
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import { BodyRecord, MeanElementRates, OrbitalElements, RotationalElements } from '../../shared/models/body.model';
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import { bodyOrientation, poleFrame } from '../../shared/rendering/body-orientation';
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import { bodyMarkerRadiusAu, systemGridRingsAu } from './system-framing';
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import { PolarGridPlane, TetherField } from './grid-plane';
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import { ExoplanetRecord } from '../../shared/models/exoplanet.model';
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@@ -51,19 +52,12 @@ const ECLIPTIC_FRAME = new THREE.Quaternion().setFromAxisAngle(new THREE.Vector3
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/**
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* Rotation carrying a moon's element frame into the scene: its local Laplace plane where JPL
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* gives one, the ecliptic otherwise. Built from the three axes {@link laplacePlaneToEquatorial}
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* sends, so the scene and the ETL's check against Horizons share the one conversion.
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* gives one, the ecliptic otherwise. {@link poleFrame} builds it from the axes
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* `laplacePlaneToEquatorial` sends, so the scene and the ETL's check against Horizons share the
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* one conversion.
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*/
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function moonFrame(body: BodyRecord): THREE.Quaternion {
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const pole = body.laplacePole;
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if (!pole) {
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return ECLIPTIC_FRAME.clone();
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}
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const axis = (x: number, y: number, z: number): THREE.Vector3 => {
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const turned = laplacePlaneToEquatorial({ x, y, z }, pole);
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return new THREE.Vector3(turned.x, turned.y, turned.z);
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};
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return new THREE.Quaternion().setFromRotationMatrix(new THREE.Matrix4().makeBasis(axis(1, 0, 0), axis(0, 1, 0), axis(0, 0, 1)));
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return body.laplacePole ? poleFrame(body.laplacePole) : ECLIPTIC_FRAME.clone();
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}
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const X_AXIS = new THREE.Vector3(1, 0, 0);
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@@ -253,32 +247,20 @@ const SPIN_AXIS = new THREE.Vector3(0, 1, 0);
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const HOURS_PER_DAY = 24;
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/**
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* How a body is turned at a given date: its own sidereal rotation, about its own axis.
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* How a body the IAU gives no rotational elements for is turned at a given date — Eris, Haumea
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* and Makemake, whose periods are known and whose poles are not: at its own sidereal rate, about
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* its orbit's normal, backwards for a negative period. None of them has an obliquity, so none is
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* applied. The phase is arbitrary: each body starts at its elements' epoch in the shortest
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* rotation of +Y onto its axis, and turns from there. Exoplanets have no published rotation at
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* all, and are left still.
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*
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* The obliquity fixes how far the pole leans from the orbit normal, and nothing more: which way
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* it leans needs the pole's right ascension, which the Horizons pages this reads do not carry. The
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* lean is taken about the orbit's ascending node because that is the one line the elements name,
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* not because the data says so — so the tilt is real and its azimuth is not. It is the node on the
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* date drawn, so the lean follows the orbit as the node turns. Likewise the phase: each body
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* starts at its elements' epoch (J2000 for the planets) in an arbitrary orientation, the
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* shortest rotation of +Y onto its axis, and turns from there. The rate and the sense are real;
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* the face towards the camera is not.
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*
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* Horizons states a retrograde spin twice over, in two conventions: an obliquity past 90 degrees
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* (Venus 177.3, Uranus 97.8) and a negative rate. Either one alone turns the body backwards, and
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* both together cancel into a forward turn — which is how Venus and Uranus were drawn. Where an
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* obliquity is given it carries the sense, and the period is taken as a magnitude; the sign of the
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* period is only read for a body with no obliquity at all.
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* Every other body is turned by {@link bodyOrientation}.
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*/
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function spinFor(elements: OrbitalElements, frame: THREE.Quaternion, rotationPeriodHours: number, obliquityDeg: number | undefined, daysSinceEpoch: number): THREE.Quaternion {
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function spinFor(elements: OrbitalElements, frame: THREE.Quaternion, rotationPeriodHours: number, daysSinceEpoch: number): THREE.Quaternion {
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const node = elements.longitudeOfAscendingNodeDeg * DEG_TO_RAD;
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const inclination = elements.inclinationDeg * DEG_TO_RAD;
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const nodeDirection = new THREE.Vector3(Math.cos(node), Math.sin(node), 0);
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const axis = new THREE.Vector3(Math.sin(inclination) * Math.sin(node), -Math.sin(inclination) * Math.cos(node), Math.cos(inclination))
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.applyAxisAngle(nodeDirection, (obliquityDeg ?? 0) * DEG_TO_RAD)
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.applyQuaternion(frame);
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const period = obliquityDeg === undefined ? rotationPeriodHours : Math.abs(rotationPeriodHours);
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const turns = (daysSinceEpoch * HOURS_PER_DAY) / period;
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const axis = new THREE.Vector3(Math.sin(inclination) * Math.sin(node), -Math.sin(inclination) * Math.cos(node), Math.cos(inclination)).applyQuaternion(frame);
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const turns = (daysSinceEpoch * HOURS_PER_DAY) / rotationPeriodHours;
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return new THREE.Quaternion()
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.setFromUnitVectors(SPIN_AXIS, axis)
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.multiply(new THREE.Quaternion().setFromAxisAngle(SPIN_AXIS, turns * 2 * Math.PI));
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@@ -297,7 +279,7 @@ interface TrackedTopLevelBody {
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position: THREE.Vector3;
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/** Sidereal rotation, where the catalogue publishes one; negative is retrograde. */
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rotationPeriodHours?: number;
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obliquityDeg?: number;
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rotationalElements?: RotationalElements;
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}
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interface TrackedMoon {
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@@ -310,7 +292,7 @@ interface TrackedMoon {
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pivot: THREE.Group;
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parentId: string;
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rotationPeriodHours?: number;
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obliquityDeg?: number;
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rotationalElements?: RotationalElements;
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/**
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* Where the moon and its planet go round a barycentre outside the planet (Charon): the moon's
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* mass over the planet's, and the planet's own small orbit round that point.
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@@ -398,7 +380,7 @@ export class SystemOrbitsRenderer {
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}
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// A body reaches here only when it has no parentBodyId, so `kind` is 'planet' or 'dwarf'.
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const kind: SystemMemberKind = body.kind;
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const tracked = this.addTopLevelBody(body.id, kind, body.orbit, body.rates, body.radiusKm, ECLIPTIC_FRAME, appearanceForBody(body, bodies, hostLuminositySolar), { periodHours: body.rotationPeriodHours, obliquityDeg: body.obliquityDeg });
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const tracked = this.addTopLevelBody(body.id, kind, body.orbit, body.rates, body.radiusKm, ECLIPTIC_FRAME, appearanceForBody(body, bodies, hostLuminositySolar), { periodHours: body.rotationPeriodHours, elements: body.rotationalElements });
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members.push({ id: body.id, kind, marker: tracked.marker });
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}
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@@ -411,7 +393,7 @@ export class SystemOrbitsRenderer {
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if (!parentTracked) {
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continue; // orphaned moon reference; skip rather than crash.
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}
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const moon = this.addMoon(body.id, body.orbit, body.rates, body.radiusKm, parentTracked, moonFrame(body), appearanceForBody(body, bodies, hostLuminositySolar), { periodHours: body.rotationPeriodHours, obliquityDeg: body.obliquityDeg }, body.massRatio);
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const moon = this.addMoon(body.id, body.orbit, body.rates, body.radiusKm, parentTracked, moonFrame(body), appearanceForBody(body, bodies, hostLuminositySolar), { periodHours: body.rotationPeriodHours, elements: body.rotationalElements }, body.massRatio);
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members.push({ id: body.id, kind: 'moon', marker: moon.marker, parentId: parent.id });
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}
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@@ -484,8 +466,10 @@ export class SystemOrbitsRenderer {
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body.position.set(orbital.x, orbital.y, orbital.z).applyQuaternion(body.frame);
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body.marker.position.copy(body.position);
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orientOrbit(body.orbitLine.quaternion, current, body.frame);
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if (body.rotationPeriodHours) {
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body.marker.quaternion.copy(spinFor(current, body.frame, body.rotationPeriodHours, body.obliquityDeg, epochJd - body.elements.epochJd));
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if (body.rotationalElements) {
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bodyOrientation(body.rotationalElements, epochJd, body.marker.quaternion);
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} else if (body.rotationPeriodHours) {
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body.marker.quaternion.copy(spinFor(current, body.frame, body.rotationPeriodHours, epochJd - body.elements.epochJd));
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}
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}
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@@ -507,8 +491,10 @@ export class SystemOrbitsRenderer {
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moon.marker.position.multiplyScalar(1 / (1 + massRatio));
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parentOrbitLine.quaternion.copy(moon.orbitLine.quaternion);
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}
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if (moon.rotationPeriodHours) {
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moon.marker.quaternion.copy(spinFor(current, moon.frame, moon.rotationPeriodHours, moon.obliquityDeg, epochJd - moon.elements.epochJd));
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if (moon.rotationalElements) {
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bodyOrientation(moon.rotationalElements, epochJd, moon.marker.quaternion);
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} else if (moon.rotationPeriodHours) {
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moon.marker.quaternion.copy(spinFor(current, moon.frame, moon.rotationPeriodHours, epochJd - moon.elements.epochJd));
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}
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}
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@@ -567,7 +553,7 @@ export class SystemOrbitsRenderer {
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radiusKm: number | undefined,
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frame: THREE.Quaternion,
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appearance?: PlanetAppearance,
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rotation?: { periodHours?: number; obliquityDeg?: number }
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rotation?: { periodHours?: number; elements?: RotationalElements }
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): TrackedTopLevelBody {
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const orbitLine = buildOrbitLine(elements, kind, frame);
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const marker = buildMarker(id, kind, radiusKm, appearance, this.deferSurface);
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@@ -575,7 +561,7 @@ export class SystemOrbitsRenderer {
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this.trackDisposable(orbitLine.geometry, orbitLine.material as THREE.Material);
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this.trackDisposable(marker.geometry, marker.material as THREE.Material);
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const tracked: TrackedTopLevelBody = { id, kind, elements, rates, marker, orbitLine, frame, position: new THREE.Vector3(), rotationPeriodHours: rotation?.periodHours, obliquityDeg: rotation?.obliquityDeg };
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const tracked: TrackedTopLevelBody = { id, kind, elements, rates, marker, orbitLine, frame, position: new THREE.Vector3(), rotationPeriodHours: rotation?.periodHours, rotationalElements: rotation?.elements };
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this.topLevelBodies.push(tracked);
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return tracked;
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}
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@@ -588,7 +574,7 @@ export class SystemOrbitsRenderer {
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parent: TrackedTopLevelBody,
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frame: THREE.Quaternion,
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appearance?: PlanetAppearance,
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rotation?: { periodHours?: number; obliquityDeg?: number },
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rotation?: { periodHours?: number; elements?: RotationalElements },
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massRatio?: number
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): TrackedMoon {
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const pivot = new THREE.Group();
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@@ -612,7 +598,7 @@ export class SystemOrbitsRenderer {
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barycentre = { massRatio, parentOrbitLine };
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}
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const moon: TrackedMoon = { id, elements, rates, marker, orbitLine, frame, pivot, parentId: parent.id, rotationPeriodHours: rotation?.periodHours, obliquityDeg: rotation?.obliquityDeg, barycentre };
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const moon: TrackedMoon = { id, elements, rates, marker, orbitLine, frame, pivot, parentId: parent.id, rotationPeriodHours: rotation?.periodHours, rotationalElements: rotation?.elements, barycentre };
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this.moons.push(moon);
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return moon;
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}
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