Description
Due to increased involvement with high-order fem codes, I guess it would be worthwhile to extend/improve high-order visualization APIs in SCOREC/Core.
At the moment we support high-order mesh visualization via the two APIs crv::writeCurvedVtuFiles (which creates tesselations of mesh tets or tris) and crv::writeCurvedWireFrame (which tesselation of mesh edges). And we don't have any simple way of visualizing high-order solution fields.
According to this (https://blog.kitware.com/modeling-arbitrary-order-lagrange-finite-elements-in-the-visualization-toolkit/) Kitware blogpost, VTK now supports arbitrary order Lagrange elements.
An example ASCII VTU file with higher order elements and fields is shown below (can also be downloaded from here
https://data.kitware.com/#collection/5a4560018d777f5e872f779e).
<VTKFile type="UnstructuredGrid" version="1.0" byte_order="LittleEndian" header_type="UInt64">
<UnstructuredGrid>
<Piece NumberOfPoints="72" NumberOfCells="5">
<PointData>
<DataArray type="Float32" Name="Ellipsoid" format="ascii">
0 0 0 0
0 0 0 0
1 1 1 1
1 1 1 1
1 1 1 1
2 2 2 2
2 2
3
0 0 0 0
1 1 1 1
1 1 1 1
3 2 2 2
2
5
0 0 0 0
1 1 1 1
2
0 0
1 1 1
2
0 0
1
0 0
1 1 1 1 1
2 2 2
</DataArray>
</PointData>
<CellData>
<DataArray type="Float32" Name="SrcCellNum" format="ascii">
0 1 2 3 4
</DataArray>
</CellData>
<Points>
<DataArray type="Float32" Name="Points" NumberOfComponents="3" format="ascii">
0 0 0
4 0 0
4 4 0
0 4 0
0 0 4
3.5 0 4.5
4.5 4.5 4.5
0 4 4
2 0 0
4 2 0
2 4 0
0 2 0
2 0 4
4 2 4
2 4 4
0 2 4
0.5 0.5 2
4 0 2
0 4 2
4 4 2
0 2 2
4 2 2
2 0 2
2 4 2
2 2 0
2 2 4
2 2 2
8 0 0
8 4 0
8 0 4
8 4 4
6 0 0
8 2 0
6 4 0
6 0 4
8 2 4
6 4 4
8 0 2
8 4 2
8 2 2
6 0 2
6 4 2
6 2 0
6 2 4
6 2 2
-1 0 0
-1 4 0
-1 4 4
-1 0 4
-1 2 0
-1 4 2
-1 2 4
-0.5 0.5 2
-1 2 2
4 -1 0
3.5 -1 4.5
2 -1 0
4 -1 2
2 -1 4
2 -1 2
0 -1 0
0 -1 4
0 -0.5 2
12 0 2
12 4 2
10 0 1
12 2 2
10 4 1
10 0 3
10 4 3
10 2 1
10 2 3
</DataArray>
</Points>
<Cells>
<DataArray type="Int64" Name="connectivity" format="ascii">
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
16 17 18 19
20 21 22 23 24 25
26
1 27 28 2
5 29 30 6
31 32 33 9
34 35 36 13
17 37 19 38
21 39 40 41 42 43
44
45 46 47 48
49 50 51 52
53
60 54 55 61
56 57 58 62
59
27 63 29 28 64 30
65 68 37
67 69 38
32 66 35
70 71 39
</DataArray>
<DataArray type="Int64" Name="offsets" format="ascii">
27 54 63 72 90
</DataArray>
<DataArray type="UInt8" Name="types" format="ascii">
72 72 70 70 73
</DataArray>
</Cells>
</Piece>
</UnstructuredGrid>
</VTKFile>
Loading that file into Paraview (version 5.8.x) produces the following pictures
- top-left: loaded into ParaView with no tessellation
- top-right: loaded into ParaView and tessellated the edges [using the "Tessellate" filter in ParaView]
- bottom-right: loaded into ParaView and tessellated the faces [using the "Tessellate" filter in ParaView]