Unwrap great-circle arc longitudes across the antimeridian so routes don't chord across the map (ISS-120)

lib/mapData.ts

@@ -74,16 +74,34 @@ export interface AirportCoord {
 // curved path the plane actually flies (same slerp as lib/sim/movement.ts).
 export const ROUTE_ARC_SEGMENTS = 24;
 
+// ISS-120 (v0.53.0): positionAt wraps each sample's longitude into [−180, 180], so an arc that
+// crosses the antimeridian jumps +179.x → −179.x between consecutive samples — and MapLibre draws
+// LineStrings as-is (no ±180 splitting), rendering a chord across the whole map. Unwrap the sample
+// sequence into continuous longitudes: keep the first sample's raw lon, then shift each subsequent
+// one by ±360 relative to the previous UNWRAPPED value until |Δlon| ≤ 180. One line stays one line;
+// out-of-range values render on MapLibre's adjacent world copies (renderWorldCopies is default-on).
+function unwrapLons(coords: [number, number][]): [number, number][] {
+  let prev = coords[0]![0];
+  for (let i = 1; i < coords.length; i++) {
+    let lon = coords[i]![0];
+    while (lon - prev > 180) lon -= 360;
+    while (prev - lon > 180) lon += 360;
+    coords[i]![0] = lon;
+    prev = lon;
+  }
+  return coords;
+}
+
 // Great-circle arc between two airports as [lon, lat] coordinates: positionAt at
-// t = i/SEGMENTS for i in 0..SEGMENTS. Pure — endpoints are exactly the airport
-// coords (positionAt returns them verbatim at t=0 and t=1).
+// t = i/SEGMENTS for i in 0..SEGMENTS. Pure — the first sample is exactly `from` and the last is
+// ≡ `to` (mod 360) (positionAt returns them verbatim at t=0 and t=1, unwrapped relative to from).
 export function greatCircleArc(from: AirportCoord, to: AirportCoord): [number, number][] {
   const coords: [number, number][] = [];
   for (let i = 0; i <= ROUTE_ARC_SEGMENTS; i++) {
     const pos = positionAt(from.lat, from.lon, to.lat, to.lon, i / ROUTE_ARC_SEGMENTS);
     coords.push([pos.lon, pos.lat]);
   }
-  return coords;
+  return unwrapLons(coords);
 }
 
 // ISS-022/025/027 (v0.22.0): the hover route trace — one great-circle LineString between two
@@ -195,6 +213,9 @@ export function queuedRoutesGeoJson(
       const arc = greatCircleArc(pts[i]!, pts[i + 1]!);
       coords.push(...(i === 0 ? arc : arc.slice(1))); // drop the duplicated joint point
     }
+    // ISS-120: each leg's arc is unwrapped relative to its OWN start airport, so at a joint the
+    // sequence can jump ±360 (leg 1 ends at dest+360k, leg 2 restarts at the raw dest) — re-unify.
+    unwrapLons(coords);
     features.push({
       type: 'Feature',
       geometry: { type: 'LineString', coordinates: coords },