Points Gaussian succeeded but Contour iso surface failed.

ParaView Support
1

Can ParaView draw an isosurface = 1 from the .VTK file attached? “Contour” filter fails. But “Legacy Reader” reads it correctly, and “Points Gaussian” represents it correctly (screen shot). So, I wonder if there is a workaround: a pre filter? a file reader? some other method?

Many thanks for your help.

STEPS TO REPRODUCE ISSUE:

  1. Download SG_sample.VTK (36.9 KB)

  2. Open SG_sample.VTK using “Legacy VTK Reader”.

  3. Select:

  •         Representation = Point Gaussian, 

  •         Coloring = sphere_markers, 

  •         Gaussian Radius = 0.04.
    Result: Correctly renders data points for 8 spheres (screen shot).
    Scalar values:
  •         0 = Blue = center of 8 spheres.

  •         1 = Yellow = points on surface of such spheres. 

  •         2 = Red = points in the space between spheres.

  1. Add filter: “Contour”.

    Result:
    Expected: Renders isosurfaces ( = 1) for 8 spheres.
    Observed: Renders a single triangle.
    Output Messages:

      Generic Warning: In /opt/glr/paraview/paraview-ci/build/superbuild/paraview/src/VTK/Common/Core/vtkMath.cxx, line 1314
      Unable to factor linear system

      Generic Warning: In /opt/glr/paraview/paraview-ci/build/superbuild/paraview/src/VTK/Filters/Core/vtkGridSynchronizedTemplates3D.cxx, line 295
      Cannot compute gradient of grid

MY SETUP:

  • ParaView Version 5.9.0-RC2 (The latest, Dec 10 2020, from https://www.paraview.org/download/ )

  • Macbook Pro Big Sur 11.0.1 (20B29)

  • Graphics: Radeon Pro 560 4 GB

SG_sample Screen Shot
SG_sample Screen Shot1490×1392 436 KB

2

I think there are a few issues here. Lets start from the top.

  • File formats in many OS’s are case sensitive. If you go File/ Open/ then look at the possible extensions, you will see that .VTK is wrong, and it should be .vtk.
  • Next, you asked for a STRUCTURED_GRID. The dimensions X, Y and Z tell you the number of points you get in the X, Y and Z direction. For a 2,2,2, you only get 8 points, and these will be in the corners of your cube. Note that ParaView used the first 8 points you gave it for the dimentions of your weird, warped cube. (Use representation Surface). Below, I will give you an example that does work of a dimension 3,3,3.
  • You can’t arbitrarily read in points in STRUCTURED_GRID. That isn’t the definition of “Structured”. You probably want some type of unstructured grid.
  • With the mesh you have, you can then run a contour. Note, again, that you may NOT add points as you have done above.

Attached is a small, toy STRUCTURED_GRID that works, 3 3 3.
sg_sample-alan.vtk (1.0 KB)

3

Thanks for your answer, Walter.

I changed my files from .VTK to .vtk to comply. Thanks for the tip.

Because Gaussian Points can read and render the file (including its extra points), I was wondering if there could be some tool (filter etc.) to convert it into an unstructured grid. If not (as it seem to be the case), I would have to bite the bullet and learn/create an unstructured grid myself as you suggest. In that case, are there any toy examples of an unstructured grid that might work?

Many thanks again for your answer.