nx_register3d.nx

nx_register3d.nx -- 3D RIGID REGISTRATION (Horn's absolute-orientation, quaternion method) -- the "align two 3D scans into one frame" capability (cadtwin: fuse multi-view/multi-scan captures of a car into ONE twin; extends nx_pc's 2D ICP to 3D). Given two corresponding 3D point sets P,Q, recovers the rotation R + translation t s.t. R*P + t ~= Q. SVD-FREE: builds Horn's 4x4 symmetric matrix N from the cross-covariance and finds its dominant eigenvector (the optimal rotation quaternion) by POWER ITERATION on a Gershgorin-shifted N (guarantees convergence to the most-positive eigenvalue). All fixed-point Q14, deterministic. Benchmarked by residual RMS. license_tier: ORIGINAL