public void getAllTerrainPatches(List<TerrainPatch> holder) {
        if (children != null) {
            for (int i = children.size(); --i >= 0;) {
                Spatial child = children.get(i);
                if (child instanceof TerrainQuad) {
                    ((TerrainQuad) child).getAllTerrainPatches(holder);
                } else if (child instanceof TerrainPatch) {
                    holder.add((TerrainPatch)child);
                }
            }
        }
    }
Retrieve all Terrain Patches from all children and store them
in the 'holder' list
@param holder must not be null, will be populated when returns
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainQuad.java