[vtkusers] suggest to vtkUnstructuredGridWriter

[David Doria]

> I use the vtkUnstructuredGridWriter to write  *.vtk files. I deleted by
> mistake all points from my polydata which is input for my unstructured
> grid with the vtkCleanPolyData. My program exited with the warning
> floating point exception. I would suggest to add a warning instead that
> there are no points. The warning should look like the warning if there
> is no input given to the writer. I think for small programs with no
> signal handling and other data checks it's not bad.

I would suggest adding the warning output and then pushing a patch to gerrit.

> And I have a question is there an easy way to find all subclasses of an
> abstract class? I think in the doxygen data base I could find it, but I
> don't know where. Has anybody a hint for my?
>

If you look at the inheritance diagram you can find all subclasses:
http://www.vtk.org/doc/nightly/html/classvtkLinearTransform.html

David