The affine mapping is ??(x)=Mx+c, where M is a 3???3 matrix and c is a vector (c0, c1, c2)T. We substitute x=?????1(u) in Equation (9), yielding: G V ??? ( ?? - 1 ??? ( u ) - p ) = 1 | M - 1 | ??? G M ??? ??? V ??? ??? M T ??? ( u - ?? ??? ( p ) ) . ( 10 ) Moreover, convolving two Gaussian functions with variance matrices V and Y results in a single Gaussian function with variance matrix V+Y: