Martin, Patch applied. Thanks !
Even > I had a similar problem when not using armadillo, but a simple > transformation does the trick. The problem is that usually the distance of > different gcps compared their absolute value is very small. > > This leads to a bad conditioned linear equation system (see > https://en.wikipedia.org/wiki/Condition_number): The first column consists > of 1s and the second and third of the x, y values of the gcps respectively. > Now if the difference of the gcps is relatively small the second and third > row are nearly colinear to the first one, hence the matrix is nearly > singular. > > The solution is to shift the coordinate system by the mean value of all gcps > and solving the modified linear equations. Since the basis function of the > TPS only depends on the difference of coordinates the resulting > transformation is the same. > > For the implementation details see the attached patch file. > > Martin -- Spatialys - Geospatial professional services http://www.spatialys.com
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