// cross product
template <typename TReal>
AI_FORCE_INLINE  aiVector3t<TReal> operator ^ ( const aiVector3t<TReal>& v1, const aiVector3t<TReal>& v2)   {
    return aiVector3t<TReal>( v1.y*v2.z - v1.z*v2.y, v1.z*v2.x - v1.x*v2.z, v1.x*v2.y - v1.y*v2.x);
}