void setClippingPlanes(GL gl) {
super.setClippingPlanes(gl);
World3D w = (World3D) world;
// don't clip in the z-direction with 2D models.
if (w.worldDepth() > 1) {
// offset the planes ever so slightly so they don't cut off the tops of the patches
renderClippingPlane
(gl, new double[]
{0.0f, 0.0, 1.0f, (float) (-(w.minPzcor() - 0.5) * WORLD_SCALE) + 0.01f},
GL.GL_CLIP_PLANE4);