add proj.wgsToMerc/mercToWgs functions

proj/proj.go

@@ -0,0 +1,19 @@
+package proj
+
+import (
+	"math"
+)
+
+const pole = 6378137 * math.Pi // 20037508.342789244
+
+func wgsToMerc(long, lat float64) (x, y float64) {
+	x = long * pole / 180.0
+	y = math.Log(math.Tan((90.0+lat)*math.Pi/360.0)) / math.Pi * pole
+	return x, y
+}
+
+func mercToWgs(x, y float64) (long, lat float64) {
+	long = 180.0 * x / pole
+	lat = 180.0 / math.Pi * (2*math.Atan(math.Exp((y/pole)*math.Pi)) - math.Pi/2)
+	return long, lat
+}

proj/proj_test.go

@@ -0,0 +1,29 @@
+package proj
+
+import (
+	"math"
+	"testing"
+)
+
+func TestWgsToMerc(t *testing.T) {
+	x, y := wgsToMerc(0, 0)
+	if x != 0 || y != 0 {
+		t.Fatalf("%v %v", x, y)
+	}
+
+	x, y = wgsToMerc(8, 53)
+	if math.Abs(x-890555.9263461898) > 1e-6 || math.Abs(y-6982997.920389788) > 1e-6 {
+		t.Fatalf("%v %v", x, y)
+	}
+}
+
+func TestMercToWgs(t *testing.T) {
+	long, lat := mercToWgs(0, 0)
+	if long != 0 || lat != 0 {
+		t.Fatalf("%v %v", long, lat)
+	}
+	long, lat = mercToWgs(890555.9263461898, 6982997.920389788)
+	if math.Abs(long-8) > 1e-6 || math.Abs(lat-53) > 1e-6 {
+		t.Fatalf("%v %v", long, lat)
+	}
+}