Changeset 7972

Timestamp:

09/06/08 13:49:54 (2 years ago)

Author:

tschaub

Message:

Adding a bit of explanation about this calcVincenty function, since distVinventy is not documented otherwise.

Files:

• trunk/openlayers/examples/measure.html (modified) (4 diffs)

trunk/openlayers/examples/measure.html

@@ -95 +95 @@
-
-        function calcVincenty(geometry) {
+            /**
+             * Note: this function assumes geographic coordinates and
+             *     will fail otherwise.  Though not documented anywhere,
+             *     OpenLayers.Util.distVincenty takes two objects representing
+             *     points with geographic coordinates and returns the geodesic
+             *     distance between them (shortest distance between the two
+             *     points on a sphere) in *kilometers*.
+             *
+             * It is important to realize that the segments drawn on the map
+             *     are *not* geodesics (or "great circle" segments).  This means
+             *     that in general, the measure returned by this function
+             *     will not represent the length of segments drawn on the map.
+             */
-            var dist = 0;
-            for (var i = 1; i < geometry.components.length; i++) {
@@ -100 +113 @@
-                var second = geometry.components[i];
-                dist += OpenLayers.Util.distVincenty(
-new OpenLayers.LonLat(first.x, first.y), 
-new OpenLayers.LonLat(second.x, second.y)
+ {lon: first.x, lat: first.y},
+ {lon: second.x, lat: second.y}
-                );
-            }
@@ -118 +131 @@
-                if (map.getProjection() == "EPSG:4326") {
-                    out += "<br /> Great Circle Distance: " + 
-
+ *
-                }        
-            } else {
@@ -162 +175 @@
-            </li>
-        </ul>
+        <p>* Note that the geometries drawn are planar geometries and the
+        metrics returned by the measure control are planar measures.  The
+        "great circle" distance does not necessarily represent the length
+        of the segments drawn on the map.  Instead, it is a geodesic metric that
+        represents the cumulative shortest path between all vertices in the
+        geometry were they projected onto a sphere.</p>
-    </div>
-  </body>