vtkCellDerivatives computes wrong results on quadratic quadrilateral cells
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
When trying to calculate the fluid strain rates on second order quadrilateral elements the PV 3.14.1 ComputeDerivatives filter produced the wrong results. I was able to reproduce the bug with a simple ramp function in y-direction in PV 3.14.1 and PV 3.10.1, c.f. y-Ramp_and_ScalarGradient_X.png and y-Ramp_and_ScalarGradient_X.pvsm in attached zip file.
I attached a patch, which fixes the mentioned bug. I did not take care about efficency concerns, however.