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

[Prof. Dr. Karl-Heinz Kunzelmann]

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 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