[Paraview] VTK XML Unstructured Grid format

[T.J. Corona]

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 <mailto: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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