[Paraview] Spatial Collection Boundary Interpolation

[Dennis Dunn]

Hello,

I have a question about loading spatial collections with XDMF. I have a 
collection of scalar fields (each saved as h5 files) and need to display 
them together as a single field. For example, a 2D global structured 
uniform grid is 64x64 cells, split into four 32x32 grids. The scalar 
data is simple cell-centered values, but I can't use the Attribute 
Center="Cell" mode because that seems to require more details like 
face/edge values and possibly the vertices. The Center="Node" method is 
simple and works since it requires only 1 scalar value per cell.

Below is the first portion of the xmf file I used to generate the 
attached image:

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE Xdmf SYSTEM "Xdmf.dtd" []>
<Xdmf xmlns:xi="http://www.w3.org/2001/XInclude" Version="2.0">
    <Domain>
       <Grid Name="Grids" GridType="Collection" CollectionType="Spatial">
          <Time Value="0.000000E+00"/>
          <Grid Name="S1" GridType="Uniform">
             <Topology TopologyType="3DCoRectMesh" Dimensions="1 32 32"/>
             <Geometry GeometryType="ORIGIN_DXDYDZ">
                <DataItem Name="Origin" Format="XML" Dimensions="3" 
NumberType="Float" Precision="8">
                  0.000000E+00  0.000000E+00  0.000000E+00
                </DataItem>
                <DataItem Name="dXdYdZ" Format="XML" Dimensions="3" 
NumberType="Float" Precision="8">
                   0.100000E-01  0.476190E-01  0.476190E-01
                </DataItem>
             </Geometry>
             <Attribute Name="U1" AttributeType="Scalar" Center="Node">
                <DataItem DataType="Float" Precision="8" Dimensions="1 
32 32" Format="HDF">
                   DATA_flow_0000_0000_0000.1.h5:/U1
                </DataItem>
             </Attribute>
             <Attribute Name="U2" AttributeType="Scalar" Center="Node">
                <DataItem DataType="Float" Precision="8" Dimensions="1 
32 32" Format="HDF">
DATA_flow_0000_0000_0000.1.h5:/U2
                </DataItem>
             </Attribute>
          </Grid>
    ... (repeat for grids S2, S3, and S4)
       </Grid>
    </Domain>
</Xdmf>

See the attached image for the result. The *.h5 supplied data points lie 
at the intersections of the visible grid lines. All the data is present, 
but ParaView 5.3.0 isn't interpolating between the different fields in 
the spatial collection, leaving very apparent gaps of width "Δx". How 
can I resolve this? I have also tried the JOIN function, but it's quite 
tricky for merging 2D/3D spatial collections. Any help you could provide 
would be greatly appreciated.

If there is no easy solution, I'll probably try parallel HDF5 to avoid 
the whole issue of xdmf spatial collections entirely.

Best regards,
-Dennis
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