// Transform the vector, skipping the translation
  VectorT<T> TransformDirection(const VectorT<T> &v) const
  {
    return VectorT<T>(
        v.x * m[_M44(0,0)] + v.y * m[_M44(0,1)] + v.z * m[_M44(0,2)],
        v.x * m[_M44(1,0)] + v.y * m[_M44(1,1)] + v.z * m[_M44(1,2)],
        v.x * m[_M44(2,0)] + v.y * m[_M44(2,1)] + v.z * m[_M44(2,2)]);
  }