Function mul_transforms 

pub fn mul_transforms(a: Transform, b: Transform) -> Transform

Multiply two transforms. If the result is applied to a point p local to frame B, the transform would first convert p to a point local to frame A, then into a point in the world frame. v2 = A.q.Rot(B.q.Rot(v1) + B.p) + A.p = (A.q * B.q).Rot(v1) + A.q.Rot(B.p) + A.p