[Paraview] VTK XML Unstructured Grid format

[Christopher Neal]

Thanks T.J.

I was just curious if the output format supported different ways of expressing the connectivity, kind of like there are flags for binary and ascii. I didn’t know if the xml *.vtu supported a classic vtk numbering. From what Armin said it looks like the offset format is the accepted and only form of the *.vtu file.

-Chris

 

From: "T.J. Corona" <tj.corona at kitware.com>
Date: Wednesday, August 24, 2016 at 2:05 PM
To: Christopher Neal <chrisneal at snumerics.com>
Cc: Benson Muite via ParaView <paraview at paraview.org>
Subject: Re: [Paraview] VTK XML Unstructured Grid format

 

Hi Chris,

 

I’m not sure I understand. As Armin mentioned:

 

a unstructured grid (without polyhedral cells) is described by three arrays:
1) connectivity: An array storing the point ids of the unique points of
                all cells.
2) offsets: An array indicating the end position of each cell in the
           connectivity array.
3) types: An array storing the types of each cell.

 

So, what you are seeing in the .vtu file is the full connectivity. If you would like the cell information in a different format, It may be best to use a vtkCellIterator and run over the vtkUnstructuredData with it. The use of vtkCellIterator is well documented in vtkCellIterator.h, though for some reason the Doxygen version of it appears incomplete.

 

Sincerely,

T.J.

 

Thomas J. Corona, Ph.D.
Kitware, Inc.
R&D Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4443

 

On Aug 24, 2016, at 1:58 PM, Christopher Neal <chrisneal at snumerics.com> wrote:

 

Thank you T.J.  

I think I see now how the information is organized via those ‘offsets’. Do you know if there is a function call that can tell it to write the actual connectivity out in full?  If it’s really obscure or would be difficult to find out, then don’t worry about it.

 

-Chris

 

From: "T.J. Corona" <tj.corona at kitware.com>
Date: Wednesday, August 24, 2016 at 12:52 PM
To: Christopher Neal <chrisneal at snumerics.com>
Cc: Benson Muite via ParaView <paraview at paraview.org>
Subject: Re: [Paraview] VTK XML Unstructured Grid format

 

Hi Chris,

 

I don’t think the line breaks represent discrete cells. If you count them, there are 32 values for the connectivity (4 cells x 8 points). 

 

Sincerely,

T.J.

 

Thomas J. Corona, Ph.D.
Kitware, Inc.
R&D Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4443

 

On Aug 24, 2016, at 12:50 PM, Christopher Neal <chrisneal at snumerics.com> wrote:

 

Hi All,

 

Does anyone have a link to an example or documentation describing how one can interpret a *.vtu file that is XML ascii? I’m looking at a file that was written for a 2x2x1 group of cells i.e. 4 hexahedral cells, and the connectivity looks like:

 

<Cells>

        <DataArray type="Int64" Name="connectivity" format="ascii" RangeMin="0" RangeMax="17">

          0 6 8 2 1 7

          9 3 2 8 10 4

          3 9 11 5 6 12

          14 8 7 13 15 9

          8 14 16 10 9 15

          17 11

        </DataArray>

        <DataArray type="Int64" Name="offsets" format="ascii" RangeMin="8" RangeMax="32">

          8 16 24 32

        </DataArray>

        <DataArray type="UInt8" Name="types" format="ascii" RangeMin="12" RangeMax="12">

          12 12 12 12

        </DataArray>

      </Cells>


I can’t seem to understand the connectivity info that is displayed. I would image there should be 8 entries per line for a hexahedral cell.


Any material on this would be greatly appreciated.

Thank you,

Chris Neal

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