onload = function (img) {
                // Getting height map data
                var canvas = document.createElement("canvas");
                var context = canvas.getContext("2d");
                if (!context) {
                    throw new Error("Unable to get 2d context for CreateGroundFromHeightMap");
                }
                var bufferWidth = img.width;
                var bufferHeight = img.height;
                canvas.width = bufferWidth;
                canvas.height = bufferHeight;
                context.drawImage(img, 0, 0);
                // Create VertexData from map data
                // Cast is due to wrong definition in lib.d.ts from ts 1.3 - https://github.com/Microsoft/TypeScript/issues/949
                var buffer = context.getImageData(0, 0, bufferWidth, bufferHeight).data;
                var vertexData = BABYLON.VertexData.CreateGroundFromHeightMap({
                    width: width, height: height,
                    subdivisions: subdivisions,
                    minHeight: minHeight, maxHeight: maxHeight, colorFilter: filter,
                    buffer: buffer, bufferWidth: bufferWidth, bufferHeight: bufferHeight
                });
                vertexData.applyToMesh(ground, updatable);
                ground._setReady(true);
                //execute ready callback, if set
                if (onReady) {
                    onReady(ground);
                }
            }
Creates a ground mesh from a height map.
tuto : http://doc.babylonjs.com/tutorials/14._Height_Map
tuto : http://doc.babylonjs.com/tutorials/Mesh_CreateXXX_Methods_With_Options_Parameter#ground-from-a-height-map
The parameter `url` sets the URL of the height map image resource.
The parameters `width` and `height` (positive floats, default 10) set the ground width and height sizes.
The parameter `subdivisions` (positive integer, default 1) sets the number of subdivision per side.
The parameter `minHeight` (float, default 0) is the minimum altitude on the ground.
The parameter `maxHeight` (float, default 1) is the maximum altitude on the ground.
The parameter `colorFilter` (optional Color3, default (0.3, 0.59, 0.11) ) is the filter to apply to the image pixel colors to compute the height.
The parameter `onReady` is a javascript callback function that will be called  once the mesh is just built (the height map download can last some time).
This function is passed the newly built mesh :
```javascript
function(mesh) { // do things
    return; }
```
The mesh can be set to updatable with the boolean parameter `updatable` (default false) if its internal geometry is supposed to change once created.