Merge branch 'main' into codex/shared-geodesy

src/data/trafficBounds.js

@@ -106,12 +106,51 @@ export function deriveFetchCenter({
   return { lat: pulled.lat, lon: pulled.lon, source: 'pulled' };
 }
 
+/**
+ * Wrapped longitude span between two meridians, in degrees.
+ *
+ * Longitude is cyclic, so a box crossing the antimeridian (±180°) has
+ * `east < west` (e.g. `west = 179.98, east = -179.98`). A plain `east - west`
+ * goes negative in that case; wrap through 360° instead.
+ *
+ * @param {number} west - West edge longitude (degrees).
+ * @param {number} east - East edge longitude (degrees).
+ * @returns {number} Span in degrees, always >= 0.
+ */
+function longitudeSpanDeg(west, east) {
+  const raw = east - west;
+  return raw >= 0 ? raw : raw + 360;
+}
+
+/** Keep a monotonic longitude range inside the traffic source's legal domain. */
+function boundedLongitudeRange(center, span) {
+  let west = center - span / 2;
+  let east = center + span / 2;
+  if (east > 180) {
+    west -= east - 180;
+    east = 180;
+  }
+  if (west < -180) {
+    east += -180 - west;
+    west = -180;
+  }
+  return { west, east };
+}
+
 /**
  * Clamp a bounding box's spans to `maxSpanDeg` and recenter it on `center`.
  *
  * Preserves the pre-C4 span semantics (each axis capped at 0.05° ≈ 5.5 km)
  * but centers the box on the derived look-at point instead of the view
- * rectangle's midpoint. Idempotent when `center` is the box's own midpoint.
+ * rectangle's midpoint. At the antimeridian the whole box shifts just far
+ * enough to remain inside [-180, 180], because the road source accepts one
+ * monotonic Overpass bounding box. Idempotent when `center` is the box's own
+ * midpoint.
+ *
+ * Longitude is handled as a cyclic axis for the span calculation, so the
+ * input span wraps correctly across the antimeridian. Output remains
+ * monotonic because callers such as `getBoundsCenter` and `boundsOverlap`
+ * rely on `west <= east`.
  *
  * @param {{south:number, west:number, north:number, east:number}} bounds
  *   Source bounds (span donor).
@@ -121,11 +160,14 @@ export function deriveFetchCenter({
  */
 export function clampBoundsAroundCenter(bounds, center, maxSpanDeg = 0.05) {
   const latSpan = Math.min(bounds.north - bounds.south, maxSpanDeg);
-  const lonSpan = Math.min(bounds.east - bounds.west, maxSpanDeg);
+  const lonSpan = Math.min(
+    longitudeSpanDeg(bounds.west, bounds.east),
+    maxSpanDeg,
+  );
+  const longitude = boundedLongitudeRange(center.lon, lonSpan);
   return {
     south: center.lat - latSpan / 2,
     north: center.lat + latSpan / 2,
-    west: center.lon - lonSpan / 2,
-    east: center.lon + lonSpan / 2,
+    ...longitude,
   };
 }