Merge pull request CesiumGS#1409 from andre-nunes/minLevel

OpenStreetMapImageryProvider can now make use of minimum level

CHANGES.md

@@ -19,6 +19,7 @@ Beta Releases
 * `TileMapServiceImageryProvider` can now handle casing differences in tilemapresource.xml.
 * Added `Quaternion.fastSlerp` and `Quaternion.fastSquad`.
 * Upgraded Tween.js to version r12.
+* `OpenStreetMapImageryProvider` now supports imagery with a minimum level.
 
 ### b24 - 2014-01-06
 

Source/Scene/OpenStreetMapImageryProvider.js

@@ -33,6 +33,7 @@ define([
      * @param {String} [description.fileExtension='png'] The file extension for images on the server.
      * @param {Object} [description.proxy] A proxy to use for requests. This object is expected to have a getURL function which returns the proxied URL.
      * @param {Extent} [description.extent=Extent.MAX_VALUE] The extent of the layer.
+     * @param {Number} [description.minimumLevel=0] The minimum level-of-detail supported by the imagery provider.
      * @param {Number} [description.maximumLevel=18] The maximum level-of-detail supported by the imagery provider.
      * @param {Credit|String} [description.credit='MapQuest, Open Street Map and contributors, CC-BY-SA'] A credit for the data source, which is displayed on the canvas.
      *
@@ -70,10 +71,21 @@ define([
         this._tileWidth = 256;
         this._tileHeight = 256;
 
+        this._minimumLevel = defaultValue(description.minimumLevel, 0);
         this._maximumLevel = defaultValue(description.maximumLevel, 18);
 
         this._extent = defaultValue(description.extent, this._tilingScheme.getExtent());
 
+        // Check the number of tiles at the minimum level.  If it's more than four,
+        // try requesting the lower levels anyway, because starting at the higher minimum
+        // level will cause too many tiles to be downloaded and rendered.
+        var swTile = this._tilingScheme.positionToTileXY(this._extent.getSouthwest(), this._minimumLevel);
+        var neTile = this._tilingScheme.positionToTileXY(this._extent.getNortheast(), this._minimumLevel);
+        var tileCount = (Math.abs(neTile.x - swTile.x) + 1) * (Math.abs(neTile.y - swTile.y) + 1);
+        if (tileCount > 4) {
+            throw new DeveloperError('Too many tiles at the minimum level');
+        }
+
         this._errorEvent = new Event();
 
         this._ready = true;
@@ -197,7 +209,7 @@ define([
         }
         //>>includeEnd('debug');
 
-        return 0;
+        return this._minimumLevel;
     };
 
     /**

Specs/Scene/OpenStreetMapImageryProviderSpec.js

@@ -224,6 +224,14 @@ defineSuite([
         expect(provider.getMaximumLevel()).toEqual(5);
     });
 
+    it('uses minimumLevel passed to constructor', function() {
+        var provider = new OpenStreetMapImageryProvider({
+            url : 'made/up/osm/server',
+            minimumLevel : 0
+        });
+        expect(provider.getMinimumLevel()).toEqual(0);
+    });
+
     it('raises error event when image cannot be loaded', function() {
         var provider = new OpenStreetMapImageryProvider({
             url : 'made/up/osm/server'