Merge pull request #45 from twpayne/initial-bearing-to

Add OpenLayers.Spherical, including utility functions for calculations on the basis of a spherical earth, patch from @twpayne

doc_config/Menu.txt

@@ -458,6 +458,7 @@ Group: OpenLayers  {
 
    File: Tween  (no auto-title, OpenLayers/Tween.js)
    File: Util  (no auto-title, OpenLayers/Util.js)
+   File: Spherical (no auto-title, OpenLayers/Spherical.js)
    File: Deprecated  (no auto-title, deprecated.js)
    }  # Group: OpenLayers
 

lib/OpenLayers.js

@@ -348,7 +348,8 @@
                 "OpenLayers/Symbolizer/Text.js",
                 "OpenLayers/Symbolizer/Raster.js",
                 "OpenLayers/Lang.js",
-                "OpenLayers/Lang/en.js"
+                "OpenLayers/Lang/en.js",
+                "OpenLayers/Spherical.js"
             ]; // etc.
         }
 

lib/OpenLayers/Spherical.js

@@ -0,0 +1,63 @@
+/* Copyright (c) 2006-2012 by OpenLayers Contributors (see authors.txt for
+ * full list of contributors). Published under the Clear BSD license.
+ * See http://svn.openlayers.org/trunk/openlayers/license.txt for the
+ * full text of the license. */
+
+/**
+ * Namespace: Spherical
+ * The OpenLayers.Spherical namespace includes utility functions for
+ * calculations on the basis of a spherical earth (ignoring ellipsoidal
+ * effects), which is accurate enough for most purposes.
+ *
+ * Relevant links:
+ * * http://www.movable-type.co.uk/scripts/latlong.html
+ * * http://code.google.com/apis/maps/documentation/javascript/reference.html#spherical
+ */
+
+OpenLayers.Spherical = OpenLayers.Spherical || {};
+
+OpenLayers.Spherical.DEFAULT_RADIUS = 6378137;
+
+/**
+ * APIFunction: computeDistanceBetween
+ * Computes the distance between two LonLats.
+ *
+ * Parameters:
+ * from   - {<OpenLayers.LonLat>} or {Object} Starting point. A LonLat or
+ *          a JavaScript literal with lon lat properties.
+ * to     - {<OpenLayers.LonLat>} or {Object} Ending point. A LonLat or a
+ *          JavaScript literal with lon lat properties.
+ * radius - {Float} The radius. Optional. Defaults to 6378137 meters.
+ *
+ * Returns:
+ * {Float} The distance in meters.
+ */
+OpenLayers.Spherical.computeDistanceBetween = function(from, to, radius) {
+  var R = radius || OpenLayers.Spherical.DEFAULT_RADIUS;
+  var sinHalfDeltaLon = Math.sin(Math.PI * (to.lon - from.lon) / 360);
+  var sinHalfDeltaLat = Math.sin(Math.PI * (to.lat - from.lat) / 360);
+  var a = sinHalfDeltaLat * sinHalfDeltaLat +
+      sinHalfDeltaLon * sinHalfDeltaLon * Math.cos(Math.PI * from.lat / 180) * Math.cos(Math.PI * to.lat / 180); 
+  return 2 * R * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)); 
+};
+
+
+/**
+ * APIFunction: computeHeading
+ * Computes the heading from one LonLat to another LonLat.
+ *
+ * Parameters:
+ * from   - {<OpenLayers.LonLat>} or {Object} Starting point. A LonLat or
+ *          a JavaScript literal with lon lat properties.
+ * to     - {<OpenLayers.LonLat>} or {Object} Ending point. A LonLat or a
+ *          JavaScript literal with lon lat properties.
+ *
+ * Returns:
+ * {Float} The heading in degrees.
+ */
+OpenLayers.Spherical.computeHeading = function(from, to) {
+    var y = Math.sin(Math.PI * (from.lon - to.lon) / 180) * Math.cos(Math.PI * to.lat / 180);
+    var x = Math.cos(Math.PI * from.lat / 180) * Math.sin(Math.PI * to.lat / 180) -
+        Math.sin(Math.PI * from.lat / 180) * Math.cos(Math.PI * to.lat / 180) * Math.cos(Math.PI * (from.lon - to.lon) / 180);
+    return 180 * Math.atan2(y, x) / Math.PI;
+};