Changeset 10110

Timestamp:

03/18/10 06:26:02 (2 years ago)

Author:

ahocevar

Message:

Give the ScaleLine control a geodesic option. Setting this to true will provide an accurate scale bar in Spherical Mercator maps. r=bartvde (closes #1890)

Location:

trunk/openlayers

Files:

• lib/OpenLayers/Control/ScaleLine.js (modified) (4 diffs)
• tests/manual/geodesic.html (added)

trunk/openlayers/lib/OpenLayers/Control/ScaleLine.js

@@ -62 +62 @@
      */
     eBottom:null,
+    
+    /**
+     * APIProperty: geodesic
+     * {Boolean} Use geodesic measurement. Default is false.
+     */
+    geodesic: false,
 
     /**
@@ -157 +163 @@
 
         // convert maxWidth to map units
-        var maxSizeData = this.maxWidth * res * inches[curMapUnits];  
+        var maxSizeData = this.maxWidth * res * inches[curMapUnits];
+        var geodesicRatio = 1;
+        if(this.geodesic === true) {
+            var maxSizeGeodesic = this.getGeodesicLength(this.maxWidth);
+            var maxSizeKilometers = maxSizeData / inches["km"];
+            geodesicRatio = maxSizeGeodesic / maxSizeKilometers;
+            maxSizeData *= geodesicRatio;
+        }
 
         // decide whether to use large or small scale units     
@@ -183 +196 @@
 
         // and to pixel units
-        var topPx = topMax / res;
-        var bottomPx = bottomMax / res;
+        var topPx = topMax / res / geodesicRatio;
+        var bottomPx = bottomMax / res / geodesicRatio;
         
         // now set the pixel widths
@@ -201 +214 @@
     }, 
 
+    /**
+     * Method: getGeodesicLength
+     * 
+     * Parameters:
+     * pixels - {Number} the pixels to get the geodesic length in meters for.
+     */
+    getGeodesicLength: function(pixels) {
+        var map = this.map;
+        var centerPx = map.getPixelFromLonLat(map.getCenter());
+        var bottom = map.getLonLatFromPixel(centerPx.add(0, -pixels / 2));
+        var top = map.getLonLatFromPixel(centerPx.add(0, pixels / 2));
+        var source = map.getProjectionObject();
+        var dest = new OpenLayers.Projection("EPSG:4326");
+        if(!source.equals(dest)) {
+            bottom.transform(source, dest);
+            top.transform(source, dest);
+        }
+        return OpenLayers.Util.distVincenty(bottom, top);
+    },
+
     CLASS_NAME: "OpenLayers.Control.ScaleLine"
 });