QUESTION / ERROR
Error message saying 'A self-intersection was detected' when trying to generate an unstructured mesh with TetGen (see Fig. 1). Why does this error occur?
Fig 1 - Error message "A self-intersection was detected"
SOLUTION
The error may be triggered by an intersection of geometries. This occurs typically when importing multiple polygons possibly in combination with polylines in a shapefile or CAD file format (.dwg/.dxf).
There are two types of intersections not allowed in the TetGen mesh generator - polylines cutting through an elemental facet or entire polygons cutting facets (see Fig 2. and Fig. 3). An intersection is identified if, for example, vertical polylines cut horizontal planes (e.g. a subvertical mine shaft cutting a polygon delineating a coal seam). If the error occurs, it is best practice to return to the supermesh and repair the input data with the GEODE supermesh repair tool. You can also take an entire step back and fix the surfaces inside your geological modeling software.
Fig. 2 - Example of intersection not allowed in the TetGen mesh generator
Fig. 3 - Example of intersections not allowed in the TetGen mesh generator
Fig. 4 - Geometries with no holes and no intersection/overlapping. The example is imported from GOCAD.
FURTHER INFORMATION & USEFUL LINKS
Manuals and Guidelines
FEFLOW 11 Documentation - The 3D Supermesh
FEFLOW 11 Documentation - 3D Supermesh Preprocessing
FEFLOW 11 Documentation - The 3D Supermesh Design
Tutorial Exercises
FEFLOW 11 Documentation - Supermesh Tutorial