pyGDML
GDML (Geometry Description Markup Language) allows to describe arbitrarily complex geometries and use them for open-source applications, e.g. such written with the help of Geant4, a popular library among paticle physicists.
Focus on tessellated solids
A tessellated solid is an arbitrarily sahped solid, which surface is approximated by facets, typically triangles.
Fixing of issues for converted gdml files
A typical pipeline to generate gdml files might go through several conversions. The original engineering drawings might be in some proprietary CAD format, e.g. SOLIDWORKS and can then be exported as STEP files. STEP is an open format. There is conversion software, e.g. MRADSim which acn then convert the STEP file into the gdml file.
The conversion is non-trivial, and there might occur a number of issues:
- invalid facets : The surfaces of the tessellated solids migth contain factes, which are too small by some metric or even degenerated.
- invalid names : The names of the invalid solids might contain invalid characters, e.g. "{"
- duplicate tessellated solids : Instead of reusing the same solid, each part migth become its own tessellated solid, even if the same part has been used somewhere within the same construction before. This is only relevant in case the file contains an assembly with multiple solids. While technically not a problem, but this increases the size of the file by a lot.
Typical outline for a gdml file
A gdml file might contain the following sections, see also the gdml manual
<gdml>
<materials>
<\materials>
<define>
<\define>
<solids>
<tessellated>
<triangular\>
...
<\tessellated>
<\solids>
<\gdml>
There are some slight differences. From the official gdml standard, only a single define section is allowed. However, sometimes during the conversion, there will be multiple define sections, one each per tessellated solid.
The default naming of the vertices after the conversion might be ambiguous.