[Paraview] VTK XML Unstructured Grid format

[Armin Wehrfritz]

Hi Chris,

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.

Regarding your example, from the "types" and "offsets" arrays you can
deduct that you have 4 cells of type "12", i.e. hexahedrons (see [1]).
Now, the offsets array tells you that the first 8 numbers in the
connectivity array are the point ids for the first cell, second number
tells you that the point ids from 9 to 16 are for the second cell and so on.
The line breaks in the connectivity array have no meaning.

HTH,
Armin

[1] 
https://gitlab.kitware.com/vtk/vtk/blob/master/Common/DataModel/vtkCellType.h





On 08/24/2016 07:50 PM, Christopher Neal 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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