# Subdomain ﬁnder for mesh generation

## Dipl.-Ing.^{in} Elisabeth Frank

**Nov. 16, 2010, 2:30 p.m. P 004**

For the mesh generation (for instance with Netgen) on a two-dimensional domain it is necessary to describe the geometry of the domain in a certain format. In particular mesh generators require subdomain information, i.e. we need to describe the boundaries and interfaces of the domain by segments and provide the subdomain on either side of a segment.

However, in practical applications the available geometry description often does not include this information directly. Moreover, we sometimes have to deal with inaccurate and non-robust data such as segments that are hidden underneath other segments or identical segments that are listed twice in the data set.

For given unsorted and disarranged data the algorithm detects and corrects inaccuracies and ﬁnds for each subdomain its bordering segments. The presented algorithm can be used for complex two-dimensional geometries consisting of lines, full circles and circle bows.