Draw each HYG star at Gaia's distance, and keep the ones Hipparcos misplaced

HYG and Gaia were both cut at 250 pc, each on its own distance. A star
Hipparcos put at 200 pc and Gaia at 300 was kept by the first, never
downloaded from the second, and drawn at 200. That is where 83% of the
9 691 mid-magnitude HYG stars without a Gaia counterpart came from, and at
the median Hipparcos had them a third too close. The mirror case, Hipparcos
outside and Gaia inside, dropped the HYG row and left its Gaia entry
anonymous.

Gaia's own Hipparcos cross-match (hipparcos2_best_neighbour, a fixed DR3
table of 99 525 rows) gives a usable Gaia distance for 97 751 of them.
placementDistancePc keeps a star either survey puts inside the cutoff, and
draws every kept star at the better measurement, inside the cutoff or not.
57 121 HYG stars now sit at Gaia's distance. 6 833 of them are past 250 pc:
Zet Per 230 -> 259 pc, 35 Ori 137 -> 330, 44 Cnc 223 -> 613, and the
farthest, HIP 69445, at 8.7 kpc. 3 666 stars that Hipparcos put outside are
now kept, and 3 656 of them give a Gaia entry its name.

The cross-match is required rather than skipped when unreachable. Without
it, every one of those stars would move back to its Hipparcos distance, and
the published map would flip with the archive's availability. The ESA TAP
answered it with a 500 at first and in 102 s on the next try. So fetches
now retry 5xx and network failures twice, after 30 s and 120 s, in the
fetch every source goes through. The refresh job also carries the Gaia DR3
responses from run to run in the Actions cache: the release is frozen, and
a live re-fetch has already reproduced stars.bin byte for byte.

423 651 stars (+10), 61 168 HYG rows folded into Gaia entries (+3 656),
351 597 unnamed designations (-3 656). 10 886 HYG survivors and 23 unmerged
pairs under an arcsecond, both inside the merge gate's ceilings. The same
1 972 exoplanets have a host; KELT-4 A b and MWC 758 c now sit on their
named star.

The HUD's "Radius" becomes "Survey radius": 250 pc is where Gaia is
surveyed to, and no longer the edge of the map.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi

src/app/features/galaxy-system/galaxy-system-scene.component.ts

@@ -1178,7 +1178,7 @@ export class GalaxySystemSceneComponent implements AfterViewInit, OnDestroy {
         { label: 'Catalogued', value: `${this.stars.length} stars` }
       ]);
       // Quotes the catalogue's own reach rather than a figure that has already been raised once.
-      this.hudNote.set(`Galactic structure is an illustrative model built on measured arm geometry — no catalogue holds the Galaxy’s stars. The ${this.stars.length} catalogued stars within ${LOCAL_GRID_RINGS_PC[LOCAL_GRID_RINGS_PC.length - 1]} pc are real.`);
+      this.hudNote.set(`Galactic structure is an illustrative model built on measured arm geometry — no catalogue holds the Galaxy’s stars. The ${this.stars.length} catalogued stars are real.`);
       return;
     }
 
@@ -1189,7 +1189,9 @@ export class GalaxySystemSceneComponent implements AfterViewInit, OnDestroy {
       // Both numbers, because they differ: the catalogue is what the map knows and the first is
       // what it draws. See `STAR_RENDER_BUDGET`.
       { label: 'Stars', value: this.starField && this.starField.drawnCount < this.stars.length ? `${this.starField.drawnCount} / ${this.stars.length}` : `${this.stars.length}` },
-      { label: 'Radius', value: `${LOCAL_GRID_RINGS_PC[LOCAL_GRID_RINGS_PC.length - 1]} pc` },
+      // The radius Gaia is surveyed to, not the edge of the map: the Hipparcos stars Gaia places
+      // further out are drawn where it places them.
+      { label: 'Survey radius', value: `${LOCAL_GRID_RINGS_PC[LOCAL_GRID_RINGS_PC.length - 1]} pc` },
       { label: 'Exoplanets', value: `${this.exoplanets.length}` },
       // The one thing the field itself cannot show: which of those points can be flown into.
       { label: 'Systems', value: `${this.enterableSystems}` }

src/app/shared/astro/star-merge.spec.ts

@@ -2,7 +2,7 @@ import { describe, expect, it } from 'vitest';
 
 import { raDegDecDistanceToXyz } from './coordinates';
 import { StarRecord } from '../models/star.model';
-import { directionCosine, isSameStar, MERGE_ANGULAR_TOLERANCE_DEG, mergeStarCatalogues } from './star-merge';
+import { directionCosine, isSameStar, MERGE_ANGULAR_TOLERANCE_DEG, mergeStarCatalogues, placementDistancePc } from './star-merge';
 
 /** A star at a given sky position and distance, which is how catalogues actually report them. */
 function at(id: number, raDeg: number, decDeg: number, distancePc: number, overrides: Partial<StarRecord> = {}): StarRecord {
@@ -237,3 +237,35 @@ describe('mergeStarCatalogues', () => {
     expect(Date.now() - started).toBeLessThan(10000);
   });
 });
+
+describe('placementDistancePc', () => {
+  it("draws a star both surveys measured at Gaia's distance", () => {
+    expect(placementDistancePc(120, 118.4, 250)).toBe(118.4);
+  });
+
+  // The case the old cut got wrong: Hipparcos inside, Gaia outside. Kept, at the distance Gaia
+  // gives, rather than at one a third short or dropped for having been misplaced.
+  it('keeps a star Hipparcos put inside the cutoff, where Gaia puts it, even past the cutoff', () => {
+    expect(placementDistancePc(200, 306, 250)).toBe(306);
+  });
+
+  // The mirror image: Hipparcos outside, Gaia inside. The Gaia download already holds the star,
+  // and keeping the HYG row is what lets the merge give that entry its name.
+  it('keeps a star only Gaia puts inside the cutoff', () => {
+    expect(placementDistancePc(262, 241, 250)).toBe(241);
+  });
+
+  it('keeps a star Gaia measured and Hipparcos gave no distance for', () => {
+    expect(placementDistancePc(undefined, 180, 250)).toBe(180);
+  });
+
+  it('falls back to Hipparcos where Gaia has no usable distance', () => {
+    expect(placementDistancePc(90, undefined, 250)).toBe(90);
+  });
+
+  it('drops a star both surveys put outside, or neither measured', () => {
+    expect(placementDistancePc(300, 410, 250)).toBeNull();
+    expect(placementDistancePc(300, undefined, 250)).toBeNull();
+    expect(placementDistancePc(undefined, undefined, 250)).toBeNull();
+  });
+});

src/app/shared/astro/star-merge.ts

@@ -67,6 +67,28 @@ export const MERGE_BRIGHTER_TOLERANCE = 1;
  */
 export const MERGE_DISTANCE_RATIO_TOLERANCE = 0.5;
 
+/**
+ * Where to draw a star Hipparcos and Gaia both measured, and whether the map keeps it at all.
+ *
+ * Gaia's distance wherever it has a usable one, since its parallaxes are fifty times more
+ * precise; Hipparcos's otherwise. The two catalogues used to be cut at the same radius, each on
+ * its own distance, so a star Hipparcos put at 200 pc and Gaia at 300 was kept by one, never
+ * downloaded from the other, and drawn at 200. That was 83% of the HYG stars left without a
+ * Gaia counterpart, and at the median Hipparcos had them at two-thirds of Gaia's distance.
+ *
+ * Now a star either survey places inside `cutoffPc` is kept, and every kept star sits where the
+ * better measurement puts it, inside the cutoff or not. `null` for a star neither survey places
+ * inside, or that no survey gives a distance for.
+ */
+export function placementDistancePc(hipparcosPc: number | undefined, gaiaPc: number | undefined, cutoffPc: number): number | null {
+  const best = gaiaPc ?? hipparcosPc;
+  if (best === undefined) {
+    return null;
+  }
+  const inside = best <= cutoffPc || (hipparcosPc !== undefined && hipparcosPc <= cutoffPc);
+  return inside ? best : null;
+}
+
 export interface MergeCandidate {
   readonly sourceId: string;
   /** Lower is better — the parallax precision this source measures with, in milliarcseconds. */