s2: Add LatLng.ApproxEqual.

Add s1.Angle.ApproxEqual too.

Signed-off-by: David Symonds <dsymonds@golang.org>

Author: nes1983

s1/angle.go

@@ -47,7 +47,7 @@ import (
 //
 //   (60*Degree).Degrees() != 60
 //
-// When testing for equality, you should allow for numerical errors (floatApproxEq)
+// When testing for equality, you should allow for numerical errors (ApproxEqual)
 // or convert to discrete E5/E6/E7 values first.
 type Angle float64
 
@@ -111,5 +111,10 @@ func (a Angle) String() string {
 	return strconv.FormatFloat(a.Degrees(), 'f', 7, 64) // like "%.7f"
 }
 
+// ApproxEqual reports whether the two angles are the same up to a small tolerance.
+func (a Angle) ApproxEqual(other Angle) bool {
+	return math.Abs(float64(a)-float64(other)) <= epsilon
+}
+
 // BUG(dsymonds): The major differences from the C++ version are:
 //   - no unsigned E5/E6/E7 methods

s2/latlng.go

@@ -93,3 +93,9 @@ func PointFromLatLng(ll LatLng) Point {
 func LatLngFromPoint(p Point) LatLng {
 	return LatLng{latitude(p), longitude(p)}
 }
+
+// ApproxEqual reports whether the latitude and longitude of the two LatLngs
+// are the same up to a small tolerance.
+func (ll LatLng) ApproxEqual(other LatLng) bool {
+	return ll.Lat.ApproxEqual(other.Lat) && ll.Lng.ApproxEqual(other.Lng)
+}

s2/latlng_test.go

@@ -150,3 +150,21 @@ func TestLatLngDistance(t *testing.T) {
 		}
 	}
 }
+
+func TestLatLngApproxEqual(t *testing.T) {
+	const ε = epsilon / 10
+	tests := []struct {
+		a, b LatLng
+		want bool
+	}{
+		{LatLngFromDegrees(30, 50), LatLngFromDegrees(30, 50+ε), true},
+		{LatLngFromDegrees(30, 50), LatLngFromDegrees(30-ε, 50), true},
+		{LatLngFromDegrees(1, 5), LatLngFromDegrees(2, 3), false},
+	}
+
+	for _, test := range tests {
+		if got := test.a.ApproxEqual(test.b); got != test.want {
+			t.Errorf("%v.ApproxEqual(%v) = %t, want %t", test.a, test.b, got, test.want)
+		}
+	}
+}

s2/rect_test.go

@@ -1108,7 +1108,7 @@ func TestDirectedHausdorffDistanceRectToRectDegenerateCases(t *testing.T) {
 		rectFromDegrees(-20, 95, 20, 105), rectFromDegrees(-30, 5, 30, 15))
 }
 
-func TestApproxEqual(t *testing.T) {
+func TestRectApproxEqual(t *testing.T) {
 	// s1.Interval and r1.Interval have additional testing.
 
 	const ε = epsilon / 10