feat: polish & windviz & deploy

internal/numerics/geometry.go

@@ -0,0 +1,41 @@
+package numerics
+
+import "math"
+
+// PointInPolygon reports whether (lat, lng) lies inside the closed polygon
+// whose vertices are given as parallel latitude/longitude slices (degrees).
+//
+// The test is ray casting in plate-carrée space. Every longitude is
+// normalised to within 180° of the first vertex before testing, so a polygon
+// spanning the antimeridian is handled correctly as long as it spans no more
+// than 180° in longitude. polyLat and polyLng must have equal length >= 3.
+func PointInPolygon(lat, lng float64, polyLat, polyLng []float64) bool {
+	n := len(polyLat)
+	if n < 3 || len(polyLng) != n {
+		return false
+	}
+	ref := polyLng[0]
+	qx := NormalizeLng(lng, ref)
+
+	inside := false
+	for i, j := 0, n-1; i < n; j, i = i, i+1 {
+		yi, yj := polyLat[i], polyLat[j]
+		xi := NormalizeLng(polyLng[i], ref)
+		xj := NormalizeLng(polyLng[j], ref)
+
+		if (yi > lat) != (yj > lat) {
+			xIntersect := (xj-xi)*(lat-yi)/(yj-yi) + xi
+			if qx < xIntersect {
+				inside = !inside
+			}
+		}
+	}
+	return inside
+}
+
+// NormalizeLng rewrites v so that it lies within 180° of ref. For example,
+// NormalizeLng(350, 10) returns -10. Used to make longitude comparisons
+// continuous across the antimeridian.
+func NormalizeLng(v, ref float64) float64 {
+	return ref + math.Mod(v-ref+540, 360) - 180
+}