@Override
    protected void controlRender(final RenderManager rm, final ViewPort vp) {

        if (!isUseRenderCamera()) {
            return;
        } else if (camera == vp.getCamera()) {
            return;
        }

        camera = vp.getCamera();
        previousCameraLocation.set(camera.getLocation());
    }
@return true to use camera from the render viewport
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainLodControl.java