Nonlinear subdivision for rational Bézier curves not working

[JHarsch (Jonas Harsch)]

As written in the blog post vtk recently supports rational Bézier cells. The two and three dimensional cells are visualized as expected by ParaView but the curve elements seem to be broken.

• Beziér curve with nonlinear subdivision level 4 is not rendered as expected. Only the control polygon is visible:

  

• Using as hotfix, the tesselate filter results in the expected visualization:

  

The VTK source file is VTK_BEZIER_CURVE_quadratic_quarter_circle.vtu.

Examplary, the surface element VTK_BEZIER_QUADRILATERAL_Piegl_figure_5.20.vtu works as expected, even for 2D surfaces embedded in 3D space:

I’m using ParaView 5.9.0 on a Windows 10 machine.

[florian360 (Florian Maurin)]

Yes, this is a known issue on our side and you already found the workaround with the tessellation filter. However, this issue is not yet reported here https://gitlab.kitware.com/vtk/vtk/-/issues so feel free to do so.

You will note that you get the same problem with Lagrange curves. The problem is that in vtkDataSetSurfaceFilter, the nonlinear subdivisions are only implemented for surfaces, but not yet for curves.

[JHarsch (Jonas Harsch)]

Thank you for the answer, I will write an vtk issue and hope for the best.