As you zoom in and pan down to the surface of the sample app, you'll note that the Earth has no elevation relief. To remedy this, you will need a surface model of the surface of the Earth. A surface model has x and y coordinates just like other layers, but it also has z values for elevation. The z values are typically in meters or feet. At first, we'll use an online service, and then we'll use a file source for offline content.
As with the other services we've been using, Esri also has some services ready for us to use; but in order to do that, we need to update our model:
Model.csand add the following
private string elevationLayerUri = "http://elevation3d.arcgis.com/arcgis/rest/services/WorldElevation3D/Terrain3D/ImageServer"; ...