double xy = quat.x*quat.y, xz = quat.x*quat.z, yz = quat.y*quat.z;
double wx = quat.w*quat.x, wy = quat.w*quat.y, wz = quat.w*quat.z;
double xy = quat.x*quat.y, xz = quat.x*quat.z, yz = quat.y*quat.z;
double wx = quat.w*quat.x, wy = quat.w*quat.y, wz = quat.w*quat.z;