Fall back to linear interpolation when interpolating in short distanc…

…es (#388). This also adds a couple of unit tests for interpolating to the beginning or end of a segment.
googlemaps · Jul 7, 2018 · d0368a4 · d0368a4
1 parent 3b8520e
commit d0368a4
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diff --git a/library/src/com/google/maps/android/SphericalUtil.java b/library/src/com/google/maps/android/SphericalUtil.java
@@ -134,7 +134,9 @@ public static LatLng interpolate(LatLng from, LatLng to, double fraction) {
         double angle = computeAngleBetween(from, to);
         double sinAngle = sin(angle);
         if (sinAngle < 1E-6) {
-            return from;
+            return new LatLng(
+                    from.latitude + fraction * (to.latitude - from.latitude),
+                    from.longitude + fraction * (to.longitude - from.longitude));
         }
         double a = sin((1 - fraction) * angle) / sinAngle;
         double b = sin(fraction * angle) / sinAngle;

diff --git a/library/tests/src/com/google/maps/android/SphericalUtilTest.java b/library/tests/src/com/google/maps/android/SphericalUtilTest.java
@@ -269,6 +269,20 @@ public void testInterpolate() {
         expectLatLngApproxEquals(
                 down,
                 SphericalUtil.interpolate(new LatLng(-45, 0), new LatLng(-45, 180), 1 / 2.0));
+
+        // boundary values for fraction, between left and back
+        expectLatLngApproxEquals(
+                left, SphericalUtil.interpolate(left, back, 0));
+        expectLatLngApproxEquals(
+                back, SphericalUtil.interpolate(left, back, 1.0));
+
+        // two nearby points, separated by ~4m, for which the Slerp algorithm is not stable and we
+        // have to fall back to linear interpolation.
+        expectLatLngApproxEquals(
+                new LatLng(-37.756872, 175.325252),
+                SphericalUtil.interpolate(
+                        new LatLng(-37.756891,175.325262),
+                        new LatLng(-37.756853,175.325242), 0.5));
     }
 
     public void testComputeLength() {