Import Upstream version 1.9.0

1 files changed, 36 insertions, 0 deletions

diff --git a/src/interpolate.js b/src/interpolate.js
new file mode 100644
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+++ b/src/interpolate.js
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+import {asin, atan2, cos, degrees, haversin, radians, sin, sqrt} from "./math";
+
+export default function(a, b) {
+  var x0 = a[0] * radians,
+      y0 = a[1] * radians,
+      x1 = b[0] * radians,
+      y1 = b[1] * radians,
+      cy0 = cos(y0),
+      sy0 = sin(y0),
+      cy1 = cos(y1),
+      sy1 = sin(y1),
+      kx0 = cy0 * cos(x0),
+      ky0 = cy0 * sin(x0),
+      kx1 = cy1 * cos(x1),
+      ky1 = cy1 * sin(x1),
+      d = 2 * asin(sqrt(haversin(y1 - y0) + cy0 * cy1 * haversin(x1 - x0))),
+      k = sin(d);
+
+  var interpolate = d ? function(t) {
+    var B = sin(t *= d) / k,
+        A = sin(d - t) / k,
+        x = A * kx0 + B * kx1,
+        y = A * ky0 + B * ky1,
+        z = A * sy0 + B * sy1;
+    return [
+      atan2(y, x) * degrees,
+      atan2(z, sqrt(x * x + y * y)) * degrees
+    ];
+  } : function() {
+    return [x0 * degrees, y0 * degrees];
+  };
+
+  interpolate.distance = d;
+
+  return interpolate;
+}