Triangle: -p switch

The -p switch

Reads a Planar Straight Line Graph (.poly) file, which can specify points, segments, holes, regional attributes, and area constraints.

Will generate a constrained Delaunay triangulation (CDT) fitting the input; or, if -s, -q, -a, or -u is used, a conforming constrained Delaunay triangulation (CCDT). If -D is used, Triangle generates a conforming Delaunay triangulation, so every triangle is Delaunay.

If -r is used with -p, the refined mesh will preserve the segments of the coarse mesh it was generated from.

If -p is not used, Triangle reads a .node file by default.