Update Sandcastle example from review.

Author: bagnell

Apps/Sandcastle/gallery/Classification Types.html

@@ -33,31 +33,31 @@
     url : 'https://beta.cesium.com/api/assets/1458?access_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJqdGkiOiIxYmJiNTAxOC1lOTg5LTQzN2EtODg1OC0zMWJjM2IxNGNlYmMiLCJpZCI6NDQsImFzc2V0cyI6WzE0NThdLCJpYXQiOjE0OTkyNjM4MjB9.1WKijRa-ILkmG6utrhDWX6rDgasjD7dZv-G5ZyCmkKg'
 }));
 
-var rectanglePrimitive;
-
 tileset.readyPromise.then(function() {
     var boundingSphere = tileset.boundingSphere;
     viewer.camera.viewBoundingSphere(boundingSphere, new Cesium.HeadingPitchRange(0.0, -0.5, boundingSphere.radius + 500.0));
     viewer.camera.lookAtTransform(Cesium.Matrix4.IDENTITY);
-
-    var center = Cesium.Ellipsoid.WGS84.cartesianToCartographic(boundingSphere.center);
-    var offset = 0.0001;
-    var rectangle = new Cesium.Rectangle(center.longitude - offset, center.latitude - offset, center.longitude + offset, center.latitude + offset);
-    rectanglePrimitive = viewer.scene.primitives.add(new Cesium.GroundPrimitive({
-        geometryInstances : new Cesium.GeometryInstance({
-            geometry : new Cesium.RectangleGeometry({
-                rectangle : rectangle
-            }),
-            attributes: {
-                color: Cesium.ColorGeometryInstanceAttribute.fromColor(new Cesium.Color(1.0, 0.0, 0.0, 0.5))
-            }
-        }),
-        classificationType : Cesium.ClassificationType.BOTH
-    }));
 }).otherwise(function(error) {
     throw(error);
 });
 
+var cartographics = [new Cesium.Cartographic(-1.3194369277314022, 0.6988062530900625),
+                     new Cesium.Cartographic(-1.3193955980204217, 0.6988091578771254),
+                     new Cesium.Cartographic(-1.3193931220959367, 0.698743632490865),
+                     new Cesium.Cartographic(-1.3194358224045408, 0.6987471965556998)];
+var rectangle = Cesium.Rectangle.fromCartographicArray(cartographics);
+var rectanglePrimitive = viewer.scene.primitives.add(new Cesium.GroundPrimitive({
+    geometryInstances : new Cesium.GeometryInstance({
+        geometry : new Cesium.RectangleGeometry({
+            rectangle : rectangle
+        }),
+        attributes: {
+            color: Cesium.ColorGeometryInstanceAttribute.fromColor(new Cesium.Color(1.0, 0.0, 0.0, 0.5))
+        }
+    }),
+    classificationType : Cesium.ClassificationType.BOTH
+}));
+
 var options = [{
     text : 'Classify Both',
     onselect : function() {