[vtkusers] XLM File Format: Unstructured Grid VTU - Detail: attributes of, , PointData and CellData

[Andy Bauer]

Hi,

You can probably ignore marking arrays as scalars, vectors, or any of the
other "active" arrays as they are not required. Marking an array with the
scalar attribute just means that a filter that is looking for a scalar
array will use the one that is marked. In your VTK code (or ParaView) you
can still mark that array later on as being the scalar array. Also, there
will be at most one scalar point data array and at most one scalar cell
data array (similar for other attributes). This attribute marking sometimes
gets confused with thinking about scalar or vector physical quantities
(e.g. temperature or velocity, respectively) but it is independent of that.
Thus you could have a temperature array and a pressure array along with
other physically scalar arrays but only one would be marked as being a VTK
scalar array and that's the one a filter would look for to do its work with
respect to.

Andy

On Sat, Mar 16, 2013 at 10:11 PM, Prof. Dr. Karl-Heinz Kunzelmann <
karl-heinz at kunzelmann.de> wrote:

> Dear all,
>
> I am in the process to write an VTU-writer for octave.
>
> Thanks to some already available examples and the
> http://www.vtk.org/VTK/img/**file-formats.pdf<http://www.vtk.org/VTK/img/file-formats.pdf>most details are clear and the raw version of my writer works so far.
>
> I have just one or two minor questions:
>
> In the documentation it is written:
>
> The following attributes of  PointData and CellData are used to specify
> the active arrays by name: Scalars, Vectors etc.
>
> Question No. 1: What is meant by "active arrays"?
>
> What is especially confusing for me are the two examples:
>
> <VTKFile type=”UnstructuredGrid” ...>
> <UnstructuredGrid>
> <Piece NumberOfPoints=”#” NumberOfCells=”#”>
> <PointData>...</PointData>
> <CellData>...</CellData>
> <Points>...</Points>
> <Cells>...</Cells>
> </Piece>
> </UnstructuredGrid>
> </VTKFile>
>
> Here the XML-Element/Node "PointData" and "CellData" do not have any
> attributes.
>
> On the other hand in the following example attributes are used:
>
> <PointData Scalars=”Temperature” Vectors=”Velocity”>
> <DataArray Name=”Velocity” .../>
> <DataArray Name=”Temperature” .../>
> <DataArray Name=”Pressure” .../>
> </PointData>
>
> What makes it so unclear for me is that the attribute "Scalars" lists only
> the name of one DataArray, but I can clearly identify two scalar dataarrays.
>
> Question No.2a and b: Why is only one scalar listed? And what would be the
> syntax for adding Pressure as well (if necessary/possible at all)?
>
> I have seen for example in the output file of the FEM program Elmer, that
> they just use the PointData element/node without any attribute.
>
> Thank you for the explanation already in advance.
>
> Sincerely
>
> Karl-Heinz Kunzelmann
>
> --
> Prof. Dr. Karl-Heinz Kunzelmann
> Poliklinik für Zahnerhaltung und Parodontologie
> Ludwig-Maximilians-Universität München
> Goethestr. 70
> D-80336 München
> Germany
>
> Tel.: +49 - 89 - 51609346
> homepage: www.kunzelmann.de
> email:  karl-heinz at kunzelmann.de
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