Polygon files are used to describe the locations of boundaries used in the TriGrid system.
The full, uncommented, version of this file is in the demodata directory in file dep.ngh.
The format is:
Line 1: NNODES - the number of nodes in the first polygon (first and last point are different, and automatically linked)
Lines 2..2+NNODES-1: X Y - the position of each node in a polygon
This sequence may be repeated a large number of times in a single polygon file.