[vtkusers] [NonLinearSubdivisionLevel] issue with quadratic meshes related to non-symmetric rotating triangulation algorithm

[John Platt]

Hi Eloi,

The treatment of quadratic cells in vtkDataSetSurfaceFilter appears to have changed between 5.8 & 5.10.

I have noticed two side effects -

    1. Point Global Ids are no longer copied.

    2. Coincident points are ALWAYS merged.

I have not reported these as bugs yet because I would like to give a suitable fix. The sticking point for me is the additional memory used by vtkUnstructuredGridGeometryFilter. I would prefer the quadratic cells to be treated as in 5.8.

If you think 2 above may be causing trouble, you could changing vtkDataSetSurfaceFilter::UnstructuredGridExecute()... 

uggf->SetPassThroughPointIds(this->PassThroughPointIds);

uggf->MergingOff(); // ** JCP ** do not merge coincident points


HTH

John.

----- Original Message ----- 
  From: Eloi Gaudry 
  To: vtkusers at vtk.org 
  Cc: Gregory Lielens 
  Sent: Thursday, January 09, 2014 9:40 AM
  Subject: [vtkusers] [NonLinearSubdivisionLevel] issue with quadratic meshes related to non-symmetric rotating triangulation algorithm


  Hi,

   

  I'm sending a small reproducer (made of a quadratic hexaedron element connected to a quadratic wedge ) for the following bug : depending on the orientation of the elements, the triangulation algorithm failed to delivers an input usable by the surface mapper with a NonLinearSubdivisionLevel >=1: 

  -          for a value of 0, the external boundaries are displayed correctly,

  -          for a value of 1, the shared faces/nodes between the hexaedron and the wedge is displayed as an external boundary (i.e. the shared faces are considered different whereas they are based on the same nodes.)

  -          for a value of 2 and more, the subdivision leads to a buggy on-screen representation.

   

  The first file (*_ok.vtk) will show the expected behavior for a NonLinearSubdvisionLevel value of 0 and 1.

  The second file (*_ko.vtk) will show the incorrect behavior for a NonLinearSubdvisionLevel value 1.

   

  If you look at the subelements used for dividing each faces of the hexaedron and the wedge (with a surface mapper and an opacity of 0.5 for instance), you will notice a mismatch between the ones created on the hexaedron and the ones created on the wedge. This leads to an incorrect vizualisation of an unshared face between both cells.

   

  Are you aware of this issue (present in 5.10.1 version at least and still there in 6.1.0.rc1) ?

  Can this easily be fixed (the behavior seen in 5.6.1 is correct for a NonLinearSubdivisionLevel value-like of 1) ?

   

  Regards,

  Eloi

   



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