Merge pull request #27 from doublestranded/bearing-destination

Bearing destination

dist/leaflet.geometryutil.js

@@ -497,6 +497,56 @@ L.GeometryUtil = L.extend(L.GeometryUtil || {}, {
             x2 = Math.cos(angleRad)*(pPoint.x-pCenter.x) - Math.sin(angleRad)*(pPoint.y-pCenter.y) + pCenter.x,
             y2 = Math.sin(angleRad)*(pPoint.x-pCenter.x) + Math.cos(angleRad)*(pPoint.y-pCenter.y) + pCenter.y;
         return map.unproject(new L.Point(x2,y2), maxzoom);
+    },
+
+    /**
+       Returns the bearing in degrees clockwise from north (0 degrees)
+       from the first L.LatLng to the second.
+       @param {L.LatLng} latlng1: origin point of the bearing
+       @param {L.LatLng} latlng2: destination point of the bearing
+       @returns {float} degrees clockwise from north.
+    */
+    bearing: function(latlng1, latlng2) {
+        var rad = Math.PI / 180,
+            lat1 = latlng1.lat * rad,
+            lat2 = latlng2.lat * rad,
+            lon1 = latlng1.lng * rad,
+            lon2 = latlng2.lng * rad,
+            y = Math.sin(lon2 - lon1) * Math.cos(lat2),
+            x = Math.cos(lat1) * Math.sin(lat2) -
+                Math.sin(lat1) * Math.cos(lat2) * Math.cos(lon2 - lon1);
+
+        var bearing = ((Math.atan2(y, x) * 180 / Math.PI) + 360) % 360;
+        return bearing >= 180 ? bearing-360 : bearing;
+    },
+
+    /**
+       Returns the point that is a distance and heading away from
+       the given origin point.
+       @param {L.LatLng} latlng: origin point
+       @param {float}: heading in degrees, clockwise from 0 degrees north.
+       @param {float}: distance in meters
+       @returns {L.latLng} the destination point.
+    */
+    destination: function(latlng, heading, distance) {
+        heading = (heading + 360) % 360;
+        var rad = Math.PI / 180,
+            radInv = 180 / Math.PI,
+            R = 6378137, // approximation of Earth's radius
+            lon1 = latlng.lng * rad,
+            lat1 = latlng.lat * rad,
+            rheading = heading * rad,
+            sinLat1 = Math.sin(lat1),
+            cosLat1 = Math.cos(lat1),
+            cosDistR = Math.cos(distance / R),
+            sinDistR = Math.sin(distance / R),
+            lat2 = Math.asin(sinLat1 * cosDistR + cosLat1 *
+                sinDistR * Math.cos(rheading)),
+            lon2 = lon1 + Math.atan2(Math.sin(rheading) * sinDistR *
+                cosLat1, cosDistR - sinLat1 * Math.sin(lat2));
+        lon2 = lon2 * radInv;
+        lon2 = lon2 > 180 ? lon2 - 360 : lon2 < -180 ? lon2 + 360 : lon2;
+        return L.latLng([lat2 * radInv, lon2]);
     }
 });
 

test/test.geometryutil.js

@@ -478,3 +478,65 @@ describe('Point rotation', function() {
     done();
   });
 });
+
+describe('Compute Bearing', function() {
+
+  it('It should be degrees clockwise from north, 0 degrees.', function(done) {
+    var latlng1 = L.latLng([0.0, 0.0]),
+        latlng2 = L.latLng([90.0, 0.0]);
+    assert.equal(0.0, L.GeometryUtil.bearing(latlng1,latlng2));
+    done();
+  });
+
+  it('Same point, should be zero.', function(done) {
+    var latlng1 = L.latLng([0.0, 0.0]),
+        latlng2 = L.latLng([0.0, 0.0]);
+    assert.equal(0, L.GeometryUtil.bearing(latlng1,latlng2));
+    done();
+  });
+
+  it('Crossing Prime Meridian.', function(done) {
+    var latlng1 = L.latLng([10.0, -10.0]),
+        latlng2 = L.latLng([-10.0, 10.0]);
+    assert.equal(134.5614514132577, L.GeometryUtil.bearing(latlng1,latlng2));
+    done();
+  });
+
+  it('Negative value for bearing greater than / equal to 180', function(done) {
+    var latlng1 = L.latLng([33.0, -120.0]),
+        latlng2 = L.latLng([34.0, -122.0]);
+    assert.equal(-58.503883697887375, L.GeometryUtil.bearing(latlng1,latlng2));
+    done();
+  });
+
+});
+
+describe('Destination', function() {
+
+  it('It should be [90.0,0.0]', function(done) {
+    var latlng1 = L.latLng([0.0, 0.0]),
+        heading = 0.0;
+        dist = 6378137 * Math.PI / 2.0; // 1/4 Earth's circumference.
+        result = L.latLng([90.0,0.0]);
+    assert.latLngEqual(result, L.GeometryUtil.destination(latlng1, heading, dist));
+    done();
+  });
+
+  it('Crossing the International Date Line', function(done) {
+    var latlng1 = L.latLng([0.0, -175.0]),
+        heading = -90.0;
+        dist = 6378137 * Math.PI / 8.0;
+        result = L.latLng([0.0, 162.5]);
+    assert.latLngEqual(result, L.GeometryUtil.destination(latlng1, heading, dist));
+    done();
+  });
+
+  it('Crossing the Prime Meridian', function(done) {
+    var latlng1 = L.latLng([10.0, -10.0]),
+        heading = 134.5614514132577;
+        dist = 3140555.3283872544;
+        result = L.latLng([-10, 10.0]);
+    assert.latLngEqual(result, L.GeometryUtil.destination(latlng1, heading, dist));
+    done();
+  });
+});