public Vec3D position(Vec3D v) {
    if (v == null) v = new Vec3D() ;
    super.position(v) ;
    if      (type == TYPE_SECTION) v.z += 1.33f ;
    else if (type == TYPE_TOWER  ) v.z += 2.50f ;
    else if (type == TYPE_SQUARE ) v.z += 1.00f ;
    return v ;
  }