Boundary markers
Boundary markers are tags used mainly to identify which output points and
edges are associated with which
PSLG
segment, and to identify which
points 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, or 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 point in an output
.node file is
chosen as follows:
- If a point 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 point lies on a PSLG segment (including the
segment's endpoints) with a nonzero boundary marker, then the point
is assigned the same marker. If the point lies on several such
segments, one of the markers is chosen arbitrarily.
- Otherwise, if the point occurs on a boundary of the triangulation,
then the point is assigned the marker one (1).
- Otherwise, the point is assigned the marker zero (0).
If you want Triangle to determine for you which points 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 points, edges,
and segments will be assigned the value one.
Return to Triangle home page.
jrs@cs.cmu.edu