added getScaleFromResolution() function to util, also added tests for both directions of the scale<->resolution tranformation functions, as well as the normalizeScale() function

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1534 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Util.js

@@ -518,6 +518,26 @@ OpenLayers.Util.getResolutionFromScale = function (scale, units) {
     return resolution;
 };
 
+/**
+ * @param {float} resolution
+ * @param {String} units Index into OpenLayers.INCHES_PER_UNIT hashtable.
+ *                       Default is degrees
+ * 
+ * @returns The corresponding scale given passed-in resolution and unit 
+ *          parameters.
+ * @type float
+ */
+OpenLayers.Util.getScaleFromResolution = function (resolution, units) {
+
+    if (units == null) {
+        units = "degrees";
+    }
+
+    var scale = 1 / (resolution * OpenLayers.INCHES_PER_UNIT[units]
+                                    * OpenLayers.DOTS_PER_INCH);
+    return scale;
+};
+
 /** Safely stop the propagation of an event *without* preventing
  *   the default browser action from occurring.
  * 

tests/test_Util.html

@@ -418,6 +418,40 @@
 
 
     }
+    
+    function test_13_Util_normalizeScale(t) {
+        t.plan(2); 
+        
+        //normal scale
+        var scale = 1/5;
+        t.eq( OpenLayers.Util.normalizeScale(scale), scale, "normalizing a normal scale does nothing");
+
+        //funky scale
+        var scale = 5;
+        t.eq( OpenLayers.Util.normalizeScale(scale), 1/5, "normalizing a wrong scale works!");
+
+
+    }
+    
+    function test_13_Util_getScaleResolutionTranslation(t) {
+        t.plan(4); 
+        
+        var scale = 1/150000000; 
+        var resolution = OpenLayers.Util.getResolutionFromScale(scale);
+        t.eq(resolution.toFixed(6), "0.476217", "Calculated correct resolution for " + scale);
+
+        var scale = 1/150000000; 
+        var resolution = OpenLayers.Util.getResolutionFromScale(scale, 'm');
+        t.eq(resolution.toFixed(6), "52916.638092", "Calculated correct resolution for " + scale);
+
+        scale = 150000000; 
+        resolution = OpenLayers.Util.getResolutionFromScale(scale);
+        t.eq(resolution.toFixed(6), "0.476217", "Calculated correct resolution for " + scale);
+
+        scale = 1/150000000; 
+        resolution = OpenLayers.Util.getResolutionFromScale(scale);
+        t.eq(OpenLayers.Util.getScaleFromResolution(resolution), scale, "scale->resolution->scale works");
+    }
 
   // -->
   </script>