[vtkusers] Compute principle curvatures with vtkcurvatures.

[Moti Freiman]

Hello!
I need to compute the principle curvatures at my software.
I saw that the vtkcurvatures class just compute the mean and Gaussian
curvatures.
When I used the formula for extracting the principle curvatures from
mean and Gaussian,  I got undefind situation (negative sqrt).
Do someone know how I can get the principle curvatures with vtk?
Thank you
Moti freiman