PUML Mesh format

SeisSol mesh format is xdmf + h5 file format. The h5 file contains the data (arrays) in binary format and the xdmf describes it. The content of an hdf5 file can be view using h5dump. The mesh file can be visualized using ParaView. The boundary conditions can be extracted from a PUML mesh and visualised in ParaView using this script.

here is an example of xdmf file (describing the hdf5 content):

<?xml version="1.0" ?>
<!DOCTYPE Xdmf SYSTEM "Xdmf.dtd" []>
<Xdmf Version="2.0">
 <Domain>
  <Grid Name="puml mesh" GridType="Uniform">
   <Topology TopologyType="Tetrahedron" NumberOfElements="901818">
    <DataItem NumberType="Int" Precision="8" Format="HDF" Dimensions="901818 4">Sulawesi:/connect</DataItem>
   </Topology>
   <Geometry name="geo" GeometryType="XYZ" NumberOfElements="159618">
    <DataItem NumberType="Float" Precision="8" Format="HDF" Dimensions="159618 3">Sulawesi:/geometry</DataItem>
   </Geometry>
   <Attribute Name="group" Center="Cell">
    <DataItem  NumberType="Int" Precision="4" Format="HDF" Dimensions="901818">Sulawesi:/group</DataItem>
   </Attribute>
   <Attribute Name="boundary" Center="Cell">
    <DataItem NumberType="Int" Precision="4" Format="HDF" Dimensions="901818">Sulawesi:/boundary</DataItem>
   </Attribute>
  </Grid>
 </Domain>
</Xdmf>

It shows that the hdf5 file consists of 4 arrays: geometry, connect, group and boundary.

geometry contains the coordinates of the nodes. Dimension: (nNodes, 3)
connect contains the volume cell connectivity. Dimension: (nCells, 4)
group contains the region id of each volume cell (different properties can then be affected on different volumes). Dimension: nCells
boundary contains the boundary conditions of each face of each volume cell. Dimension: nCells.

Each tetrahedron has 4 faces. In our format, the 4 boundary condition ids (4 bits each) are store within a single integer (16 bits) variable. The values can be unpacked, for example in python using:

for faceId in range(0,4):
   boundaryFace[faceId] = (boundary >> (faceId*8)) & 0xFF;

The possibles values of the boundary condition ids range from 0 to 255.
In SeisSol, boundary conditions are historically tagged as:
0: regular
1: free surface
3: dynamic rupture
5: absorbing
6: periodic
n>6: dynamic rupture (See Fault tagging)

Here is the convention defining the face id in a tetrahedron:

s_vert[0,:] = [0,2,1];   s_vert[1,:] = [0,1,3];    s_vert[2,:] = [1,2,3]; s_vert[3,:] = [0,3,2];