- IsPointInPolygon added

utils/utils_geo.go

@@ -0,0 +1,33 @@
+package utils
+
+// http://ju.outofmemory.cn/entry/130555
+func IsPointInPolygon(x float64, y float64, points [][2]float64) bool {
+	count := 0
+	x1, y1 := points[0][0], points[0][1]
+	x1Part := (y1 > y) || ((x1-x > 0) && (y1 == y))
+	var a = [2]float64{x1, y1}
+	p := append(points, a)
+	for i := range p {
+		if i == 0 {
+			continue
+		}
+		point := p[i]
+		x2, y2 := point[0], point[1]
+		x2Part := (y2 > y) || ((x2 > x) && (y2 == y))
+		if x2Part == x1Part {
+			x1, y1 = x2, y2
+			continue
+		}
+		mul := (x1-x)*(y2-y) - (x2-x)*(y1-y)
+		if mul > 0 {
+			count++
+		} else {
+			if mul < 0 {
+				count--
+			}
+		}
+		x1, y1 = x2, y2
+		x1Part = x2Part
+	}
+	return count == 2 || count == -2
+}