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frontend/src/components/MainMap.tsx

@@ -121,13 +121,21 @@ export function MainMap({ fromGrid, toGrid, fromLabel, toLabel, beamAzimuths, be
     // ── Antenna beam lobe(s) (drawn first, under the arc/markers) ──
     if (from && beamAzimuths && beamAzimuths.length) {
       const half = (beamWidth ?? 30) / 2;
-      const D = 5500; // lobe length (km) — short enough to rarely reach a pole
-      const radial = (b: number): [number, number][] =>
-        Array.from({ length: 14 }, (_, i) => {
-          const d = destinationPoint(from.lat, from.lon, b, (D * (i + 1)) / 14);
-          return [d.lat, d.lon] as [number, number];
-        });
-      const edge = { color: '#dc2626', weight: 1.5, opacity: 0.6 };
+      const D = 5500; // lobe length (km)
+      // A great circle pointing poleward runs to lat ±90, where Mercator is
+      // infinite — the line then snaps across the top of the map. Generate the
+      // radial with plenty of points (smooth curve) and STOP it just before the
+      // pole, so a north/south beam draws a clean line toward the edge instead.
+      const radial = (b: number): [number, number][] => {
+        const pts: [number, number][] = [];
+        const N = 64;
+        for (let i = 1; i <= N; i++) {
+          const d = destinationPoint(from.lat, from.lon, b, (D * i) / N);
+          pts.push([d.lat, d.lon]);
+          if (Math.abs(d.lat) > 86) break; // near a pole — stop before the snap
+        }
+        return pts;
+      };
       for (const az of beamAzimuths) {
         const arc: [number, number][] = [];
         for (let b = az - half; b <= az + half + 0.001; b += 2) {
@@ -140,13 +148,10 @@ export function MainMap({ fromGrid, toGrid, fromLabel, toLabel, beamAzimuths, be
           ...arc,
           ...radial(az + half).reverse(),
         ]);
-        // A geodesic lobe that reaches near a pole can't be filled on a
-        // Mercator map without the polygon snapping across the whole world —
-        // draw just the two edges in that case; otherwise the translucent lobe.
-        if (ring.some(([la]) => Math.abs(la) > 82)) {
-          L.polyline(unwrapLon([[from.lat, from.lon], ...radial(az - half)]) as L.LatLngExpression[], edge).addTo(wo);
-          L.polyline(unwrapLon([[from.lat, from.lon], ...radial(az + half)]) as L.LatLngExpression[], edge).addTo(wo);
-        } else {
+        // Near a pole the lobe's two edges diverge wildly (one runs NW, the
+        // other NE) and look broken on a Mercator map — so for a poleward beam
+        // show ONLY the clean boresight (below). Otherwise draw the filled lobe.
+        if (!ring.some(([la]) => Math.abs(la) > 78)) {
           L.polygon(ring as L.LatLngExpression[], {
             color: '#dc2626', weight: 1, opacity: 0.5, fillColor: '#dc2626', fillOpacity: 0.14,
           }).addTo(wo);