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Tint a star measured in Gaia's BP−RP as the B−V of the dwarf of that colour

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colorIndexToRgb maps a B−V onto the star field's tint ramp, and its one caller passed it every
star's colour index, whatever colorSystem said. BP−RP is the larger of the two for the same star —
0.823 against 0.65 for a G2 dwarf, 1.84 against 1.42 for an M0 (Pecaut & Mamajek) — so the 376 703
stars measured in it, 83 % of the catalogue, were tinted as later types than they are, and redder
than HYG's stars of the same type, and than their own disc in the system view.

A BP−RP is now carried to the B−V of the dwarf sequence at that colour (the table's own B−V
column, which DwarfSequencePoint now returns, clamped at its ends), then tinted as before. The
median Gaia colour, BP−RP 0.883, a G7 dwarf, read as a K2: its tint goes from (1, 0.972, 0.955) to
(0.975, 0.982, 1), the same as HYG's G7 stars.

Controls, each failing its named test: BP−RP read as B−V (2 of 792 failed), the star field not
passing the colour system (1 of 792), and the B−V taken from the wrong column (3 of 792).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Senrokai
2026-09-29 20:31:27 +02:00
co-authored by Claude Opus 5.5
parent fa52f6a818
commit 4191b70e63
4 changed files with 34 additions and 7 deletions
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src/app/features/galaxy-system/star-field-renderer.ts
+10 -4
View File
@@ -2,7 +2,7 @@ import * as THREE from 'three/webgpu';
import { float, instancedBufferAttribute, mix, modelViewMatrix, smoothstep, uniform, uv, vec2, vec4 } from 'three/tsl';
import { BrightnessIndex, brightnessIndex, Positioned } from '../../shared/astro/brightest';
import { spectralTypeToColorIndex } from '../../shared/astro/spectral';
import { dwarfSequenceAtColor, spectralTypeToColorIndex } from '../../shared/astro/spectral';
import { SceneCamera } from '../../core/engine/engine.service';
import { StarRecord } from '../../shared/models/star.model';
import { PIXELS_TO_ANGULAR_SIZE, REFERENCE_FOV_DEGREES, REFERENCE_VIEWPORT_HEIGHT_PX } from './angular-size';
@@ -109,9 +109,15 @@ const WARM_STAR_COLOR = new THREE.Color(1.0, 0.6, 0.35);
* value derived from `spectralType`, and to neutral white only when the catalog records no
* classification at all — never to 0, which is itself a real color index meaning "hot A-type"
* and would paint several hundred red dwarfs blue-white.
*
* A Gaia BP−RP is carried to the B−V of the dwarf of that colour first. It is the larger of the
* two for the same star — 0.82 against 0.65 for a G2 dwarf, 1.84 against 1.42 for an M0 — and read
* as B−V it tinted the 376 703 stars measured in it, 83 % of the map, as a K2 where they were a G7
* at the median, and an M0 dwarf as an M5.
*/
export function colorIndexToRgb(colorIndex: number | null, spectralType?: string): THREE.Color {
const resolved = colorIndex ?? spectralTypeToColorIndex(spectralType);
export function colorIndexToRgb(colorIndex: number | null, spectralType?: string, colorSystem?: 'B-V' | 'BP-RP'): THREE.Color {
const measured = colorIndex !== null && colorSystem === 'BP-RP' ? dwarfSequenceAtColor(colorIndex, 'BP-RP', true)!.bMinusV : colorIndex;
const resolved = measured ?? spectralTypeToColorIndex(spectralType);
const color = new THREE.Color();
if (resolved === null) {
return color.copy(NEUTRAL_STAR_COLOR);
@@ -295,7 +301,7 @@ export class StarFieldRenderer {
this.catalogueColors = new Float32Array(catalogue.length * 3);
this.catalogueSizes = new Float32Array(catalogue.length);
catalogue.forEach((star, index) => {
const color = colorIndexToRgb(star.colorIndex, star.spectralType);
const color = colorIndexToRgb(star.colorIndex, star.spectralType, star.colorSystem);
this.catalogueColors[index * 3] = color.r;
this.catalogueColors[index * 3 + 1] = color.g;
this.catalogueColors[index * 3 + 2] = color.b;