Moritz Lennert wrote: > Can someone explain what is the meaning of the forward and (especially) > backward errors in georectify/g.transform ?
Given a set of GCPs, each with source and destination coordinates, best-fit forward and reverse transformations are computed. The forward error is the distance between the the forward-transformed source coordinates and the corresponding destination coordinates, while the backward error is the distance between the source coordinates and the reverse-transformed destination coordinates. > Also, is it normal that the backward error is significantly (by one order > of magnitude) lower than the forward error ? I don't know about "normal", but it isn't unlikely. The best-fit polynomial for one transformation may be a much closer fit than for its inverse. In particular, the inverse of a polynomial containing 2nd- or 3rd-order terms won't itself be a polynomial. -- Glynn Clements <[EMAIL PROTECTED]> _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
