Timestep in FieldData

ParaView Support
1

I’m trying to understand how to Use FieldData and other possible uses of FieldData.

I understand that one of the main uses is to store the time or timesteps associated with a file. However, I’m not sure if there is a specific format or specification for doing this. For example, when I export data from ParaView from example data created by some other solver, the FieldData contains both TimeValue and TIME.

    <FieldData>
      <DataArray type="Float64" Name="TIME" NumberOfTuples="1" format="ascii" RangeMin="0.00022002" RangeMax="0.00022002">
        0.00022002
      </DataArray>
      <DataArray type="Float64" Name="TimeValue" NumberOfTuples="1" format="ascii" RangeMin="1" RangeMax="1">
        1
      </DataArray>
    </FieldData>

In this example, TIME is the real time in seconds whereas TimeValue seems to be the file number in the group of files. But why is TimeValue an Int stored as a Float? I’m not sure what Is going on here - Do I always need to include TIME and TimeValue? Or is one of the two sufficient for ParaView to figure out what is going on?

And what about NumberOfTuples? Wil this always be 1? Can you have FieldData that has more than one tuple?

There’s not much documentation on this, or at least not that I could easily find anyway.

The last part of my question is what else can you use FieldData for? Is there a good example xml file showing it’s usage?

2

The XML readers exploit the “TimeValue” field data information to provide the right temporal information to VTK pipeline, which in turn is used by ParaView.

I do not see any usage of “TIME” anywhere.

And what about NumberOfTuples? Wil this always be 1? Can you have FieldData that has more than one tuple?

Yes, not an issue.

There’s not much documentation on this, or at least not that I could easily find anyway.

This is because this is not about VTK and ParaView but about the XML readers that treat this data from file and then pass it down to VTK.

This TimeValue mechanism is documented here: VTK: Field Data as Time Meta-Data in VTK XML File Formats.

Other usage of FieldData in ParaView is classicaly the composite dataset where field data is used to color block by block.

There is however currently an issue with that: https://gitlab.kitware.com/paraview/paraview/-/issues/20748

3

Thanks. After looking at this in a bit more detail now I believe the reason I have TIME and TimeValue is because the file was originally read in from the legacy format and then later exported in the newer XML format and the conversion was not made automatically within ParaView it seems.

But I think my confusion is cleared up.

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