Preprocess CP2TFORM

When CP2TFORM is used in piecewise linear image transformation mode, it uses triangulation to calculate the local image transformation. Sometimes a good triangulation of basepoints gives folded triangles when used with the input points. The function CP2TFORM try's to remove the controlpoints causing the folding, but often fails with the error:

Eliminated * control point pair(s).
Fold-over triangles remain. See CP2TFORM reference page.

This function PreProcessCp2tform removes all control points which cause fold-over triangles with cp2tform.

example code :
xy=[input_points2(:,2) input_points2(:,1)];
uv=[base_points2(:,2) base_points2(:,1)];
[xy uv]=PreProcessCp2tform(xy,uv);
trans_prj = cp2tform(xy,uv,'piecewise linear');
J = imtransform(I,trans_prj,'Xdata',[1 100],'YData',[1 100],'XYscale',1);