Triangle: Boundary markers (original) (raw)
Boundary markers
Boundary markers are tags used mainly to identify which output vertices and edges are associated with whichPSLG segment, and to identify which vertices and edges occur on a boundary of the triangulation. A common use is to determine where boundary conditions should be applied to a finite element mesh. You can prevent boundary markers from being written into files produced by Triangle by using the -B switch.
The boundary marker associated with each segment in an output.poly file and each edge in an output.edge file is chosen as follows:
- If an output edge is part or all of a PSLG segment with a nonzero boundary marker, then the edge is assigned the same marker as the segment.
- Otherwise, if the edge occurs on a boundary of the triangulation (including boundaries of holes), then the edge is assigned the marker one (1).
- Otherwise, the edge is assigned the marker zero (0). The boundary marker associated with each vertex in an output.node file is chosen as follows:
- If a vertex is assigned a nonzero boundary marker in the input file, then it is assigned the same marker in the output.node file.
- Otherwise, if the vertex lies on a PSLG segment (including the segment's endpoints) with a nonzero boundary marker, then the vertex is assigned the same marker. If the vertex lies on several such segments, one of the markers is chosen arbitrarily.
- Otherwise, if the vertex occurs on a boundary of the triangulation, then the vertex is assigned the marker one (1).
- Otherwise, the vertex is assigned the marker zero (0). If you want Triangle to determine for you which vertices and edges are on the boundary, assign them the boundary marker zero (or use no markers at all) in your input files. In the output files, all boundary vertices, edges, and segments will be assigned the value one.