How to save selection as polydata vtk file instead of unstructured grid vtk file?

Hi,

I want to extract some points from a tetrahedral mesh and save the selection as a Polydata vtk file. I used Select Points Through and then Extract Selection. I try to save it as vtk file, but it can only be saved as Unstructured Grid vtk. How can I save it as Polydata vtk?
Thanks!

Gening

Hi @Gening_Dong,

Welcome to the ParaView discourse and thanks for posting about your problem!

The “Extract Surface” filter will take you from a vtkUnstructuredGrid to a vtkPolyData keeping in mind that a vtkPolyData is necessarily a geometrical object with dimension inferior to 3.

Hope that helps!

Best regards,

Julien

Hi @jfausty ,

Thanks for the reply! I want to extract a volume of nodes (see screenshots below) and cannot directly “Extract Surface”. When I used the “Extract Selection” first and then “Extract Surface”, I was able to output is as vtkPolyData. However, the blocks of that vtkPolyData file seems weird since I think it should contain the location/coordinates of those nodes (see the screenshot below).
What can I do?

Best,
Gening

Screenshot 2022-10-27 181401
Screenshot 2022-10-27 190806

Hi @Gening_Dong,

May I ask why you need the extraction to be a vtkPolyData and not a vtkUnstructuredGrid?

If you are only interested in the points you can use the “Convert To Point Cloud” filter on the extracted vtkUnstructuredGrid to obtain a vtkPolyData containing only points.

Best regards,

Julien

Hi, I’d like to make the extracted points into a separate surface for a specific boundary condition in a CFD/FSI simulation. I think I should select cells instead of points. Thanks for the suggestion.

Hi again @Gening_Dong,

I think I see what you would like to do.

You might want to select the cells, perform an Extract Selection and then an Extract Surface to only get the outside surface of that selection as a vtkPolyData.

Hope that helps!

Best regards,

Julien

That’s exactly what I want to do and it works! Thanks so much for your help!