Triangle's default behavior is to find the Delaunay
triangulation of a set of vertices. Store the vertices in a
.node file, such as spiral.node, illustrated below. The command
triangle spiralproduces the Delaunay triangulation, also
illustrated below. To triangulate a PSLG instead, describe the
geometry of the region you wish to mesh in a .poly file, such as
face.poly, illustrated below. Use the -p switch to specify that
the input is a PSLG (.poly file) rather than a vertex set (.node
file). The command triangle -p facewill produce the constrained
Delaunay triangulation, with holes and concavities removed. (The
mouth and eye holes are specified in the input file; the
concavities are removed automatically.) The automatic removal of
concavities from the triangulation will be detrimental if you
have not taken care to surround the area to be triangulated with
segments. In the next example, the input file box.poly defines
an open region, so the -c switch must be used to prevent the
automatic removal of concavities