Relative positioning from model indexing

摘要

Cross ratios of image points are viewpoint invariants if the points are coplanar in 3D. If points are in general position in 3D, cross ratios will still be unaffected by intrinsic camera parameters and camera rotation, assuming linear imaging. The variation of cross ratios with viewpoint is therefore due entirely to the shift in relative position of the camera to the points in 3D. By inverting this relationship, we can compute camera position relative to a model of the environment using indexing methods. This computation is then independent of camera calibration.