VTK  9.0.1
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1 Field Data as Time Meta-Data in VTK XML File Formats
2 ====================================================
3 
4 As of VTK 8.2, VTK XML readers and writers support embedding time
5 meta-data as a field array. This is demonstrated best with an example:
6 
7  <VTKFile type="PolyData" version="1.0" byte_order="LittleEndian" header_type="UInt64">
8  <PolyData>
9  <FieldData>
10  <DataArray type="Float64" Name="TimeValue" NumberOfTuples="1">1.24
11  </DataArray>
12  </FieldData>
13  ...
14  </VTKFile>
15 
16 Here TimeValue is a regular double precision array that has a single value of 1.24.
17 The XML readers will treat this array in a special way. When they encounter this array
18 during the meta-data stage (`RequestInformation()`), they will read the value from
19 this array and generate a `vtkStreamingDemandDrivenPipeline::TIME_STEPS()` key
20 in the output information containing this value.
21 
22 In addition, the XML writers will generate a field array of name TimeValue in the
23 output, if they encounter time value in their input (`vtkDataObject::DATA_TIME_STEP()`).
24 This is done even if the data does not have a TimeValue array. Furthermore, even such
25 an array exists, it will be replaced with one that contains the value from
26 `vtkDataObject::DATA_TIME_STEP()` to make sure that the value is consistent with the
27 pipeline value.
28 
29 This change may appear pointless on its own as a single time value is not very useful.
30 Its main use is when reading file series as it is done by ParaView's file (time) series
31 readers.