[Paraview] XDMF and nested Grid Collections

[Alessandro De Maio]

Hi,

I'm trying to export from a parallel MPI CFD code a set of results using
xdmf/hdf5 format in order to be read in Paraview.
The computational domain is divided into several parts (unstructured
polyhedral grid) and the idea is to write a xdmf  with a further
subdivision to be read in parallel by mpi paraview.
So it's a nested subdivision in which the external level is based on
different parts of the domain (that should be extractable in Paraview after
the reading) and each part is divided into a number of chunks equal to the
number of processes of the parallel Paraview execution. With such a
subdivision, reading this file with a parallel Paraview execution, each
Paraview process loads a fraction of each part and, if all the chunks of
each part have the same dimension, all the Paraview processes are balanced.

In the following there is an example for two parts and two Paraview
processes.

I've used nested Grid Collections of type Spatial and it seems that
everything is ok but the problem is that in Paraview the names of the first
level collection items  is lost (in the following example  tet_cell1 and
tet_cell2) and these items are called "Block 0" and "Block 1". The leaf
elements of the tree instead (Grid_01, Grid_02, ...) mantain their correct
name.

I've tried also to change the GridType of the external level from
Collection to Tree (that should be supported in the xdmf data format) but
in this case the item in Paraview is empty (0 cells and 0 nodes).

Is there any error in my procedure? It's the first time that I use xdmf.

Thank you in advance for your help.

Alessandro



<?xml version="1.0" encoding="utf-8"?>
<Xdmf xmlns:xi="http://www.w3.org/2001/XInclude" Version="3.3">
  <Domain>
    <Grid Name="all" GridType="Collection" CollectionType="Spatial">
      <Grid Name="tet_cell1" GridType="Collection" CollectionType="Spatial">
        <Grid Name="Grid_01" GridType="Uniform">
          <Geometry Origin="" Type="XYZ">
            <DataItem DataType="Float" Dimensions="89724 3" Format="HDF"
Precision="4">../positive/xdmf/tet_cell1.h5:Data0</DataItem>
          </Geometry>
          <Topology Dimensions="16797" Type="Mixed">
            <DataItem DataType="Int" Dimensions="1271390" Format="HDF"
Precision="8">../positive/xdmf/tet_cell1.h5:Data1</DataItem>
          </Topology>
          <Attribute Center="Node" Name="pressure-udf" Type="None">
            <DataItem DataType="Float" Dimensions="89724" Format="HDF"
Precision="4">../positive/xdmf/tet_cell1.h5:Data2</DataItem>
          </Attribute>
        </Grid>

        <Grid Name="Grid_02" GridType="Uniform">
          <Geometry Origin="" Type="XYZ">
            <DataItem DataType="Float" Dimensions="31633 3" Format="HDF"
Precision="4">../negative/xdmf/tet_cell1.h5:Data0</DataItem>
          </Geometry>
          <Topology Dimensions="5866" Type="Mixed">
            <DataItem DataType="Int" Dimensions="444229" Format="HDF"
Precision="8">../negative/xdmf/tet_cell1.h5:Data1</DataItem>
          </Topology>
          <Attribute Center="Node" Name="pressure-udf" Type="None">
            <DataItem DataType="Float" Dimensions="31633" Format="HDF"
Precision="4">../negative/xdmf/tet_cell1.h5:Data2</DataItem>
          </Attribute>
        </Grid>
      </Grid>

      <Grid Name="tet_cell2" GridType="Collection" CollectionType="Spatial">

        <Grid Name="Grid_01" GridType="Uniform">
          <Geometry Origin="" Type="XYZ">
            <DataItem DataType="Float" Dimensions="87146 3" Format="HDF"
Precision="4">../positive/xdmf/tet_cell2.h5:Data0</DataItem>
          </Geometry>
          <Topology Dimensions="16407" Type="Mixed">
            <DataItem DataType="Int" Dimensions="1234254" Format="HDF"
Precision="8">../positive/xdmf/tet_cell2.h5:Data1</DataItem>
          </Topology>
          <Attribute Center="Node" Name="pressure-udf" Type="None">
            <DataItem DataType="Float" Dimensions="87146" Format="HDF"
Precision="4">../positive/xdmf/tet_cell2.h5:Data2</DataItem>
          </Attribute>
        </Grid>

        <Grid Name="Grid_02" GridType="Uniform">
          <Geometry Origin="" Type="XYZ">
            <DataItem DataType="Float" Dimensions="30317 3" Format="HDF"
Precision="4">../negative/xdmf/tet_cell2.h5:Data0</DataItem>
          </Geometry>
          <Topology Dimensions="5661" Type="Mixed">
            <DataItem DataType="Int" Dimensions="425050" Format="HDF"
Precision="8">../negative/xdmf/tet_cell2.h5:Data1</DataItem>
          </Topology>
          <Attribute Center="Node" Name="pressure-udf" Type="None">
            <DataItem DataType="Float" Dimensions="30317" Format="HDF"
Precision="4">../negative/xdmf/tet_cell2.h5:Data2</DataItem>
          </Attribute>
        </Grid>

      </Grid>
    </Grid>

  </Domain>
</Xdmf>
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