chore: release v0.27.12

frontend/src/lib/maidenhead.ts

@@ -172,6 +172,50 @@ export function greatCirclePoints(
   return out;
 }
 
+// splitAtAntimeridian cuts a continuous (unwrapped) path into the pieces that
+// fit on a map showing ONE world, each piece with longitudes back inside ±180.
+//
+// greatCirclePoints deliberately lets longitude run past ±180 so the polyline
+// stays smooth. That is right for a map with repeating world copies, and wrong
+// for one without: an arc from Australia to South America came out at 190°,
+// 210°, 250° — drawn into the empty space off the right-hand edge, ending
+// nowhere, while its own end marker sat correctly on the far left. From VK,
+// where most paths cross the antimeridian, that was most of the map's arcs.
+//
+// Each crossing ends one piece at exactly ±180 and starts the next at the
+// opposite edge, at the SAME latitude, so the line leaves one side of the map
+// and re-enters the other at the height it left. Leaflet takes the result as a
+// multi-polyline, so one path is still one layer.
+export function splitAtAntimeridian(pts: [number, number][]): [number, number][][] {
+  if (pts.length === 0) return [];
+  // Which copy of the world a longitude belongs to: 0 is the map's own.
+  const world = (lon: number) => Math.floor((lon + 180) / 360);
+  const norm = (lon: number) => lon - 360 * world(lon);
+  const out: [number, number][][] = [];
+  let cur: [number, number][] = [];
+  for (let i = 0; i < pts.length; i++) {
+    const [lat, lon] = pts[i];
+    if (i > 0) {
+      const [pLat, pLon] = pts[i - 1];
+      const wPrev = world(pLon), wCur = world(lon);
+      if (wPrev !== wCur) {
+        const east = wCur > wPrev;
+        // The meridian actually crossed, in unwrapped degrees.
+        const edge = 180 + 360 * Math.min(wPrev, wCur);
+        const f = (edge - pLon) / (lon - pLon);
+        const edgeLat = pLat + f * (lat - pLat);
+        cur.push([edgeLat, east ? 180 : -180]);
+        out.push(cur);
+        cur = [[edgeLat, east ? -180 : 180]];
+      }
+    }
+    cur.push([lat, norm(lon)]);
+  }
+  if (cur.length > 1) out.push(cur);
+  else if (cur.length === 1 && out.length === 0) out.push(cur);
+  return out;
+}
+
 function toRad(d: number): number { return (d * Math.PI) / 180; }
 function toDeg(r: number): number { return (r * 180) / Math.PI; }