Pairwise alignment
	Absolute orientation [Arun et al., PAMI 1987] [Horn et al., JOSA A 1988], Procrustes Algorithm [Golub & VanLoan] Given two sets of matching points, compute R    pi’ = R pi       with 3D rays      pi = N(xi,yi,zi) = N(ui-uc,vi-vc,f)    A = Σi pi pi’T = Σi pi piT RT = U S VT = (U S UT) RT    VT = UT RT    R = V UT