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 fitting the input; or, if -q or -a is used (for quality meshing), a conforming Delaunay triangulation.
• If -r is used, the refined mesh will preserve the segments of the coarse mesh it was generated from.
• If -p is not used, Triangle will read a .node file by default.