Understanding Polygon Mask (*.PLY) Files

Polygons are ASCII files with default extension .ply. A polygon file contains a list of X,Y coordinates that define one or more polygons. The file may contain any number of polygons, and each polygon may have any number of vertices. The first and last points in each polygon are assumed to connect. If the file will contain more than one polygon, each polygon must start with a line 'poly #' ('p' or 'P' in column 1). Comment lines are indicated by a '/' in column 1.

Clip polygon files may also be generated interactively by using the digitising tools in the Map Tools menu.

Example of a single polygon file:

/ Sample single polygon file

/----------------------------

4325.2 8421.8

6800 8421.8

6850 4000

4300 4000

Example of a three-polygon file:

/ Sample three polygon file
/---------------------------
poly
4325.2 8421.8
6800 8421.8
6850 4000
4300 4000
poly
7000 8421.8
8000 8421.8
8000 4000
7000 4000
poly
7000 10421.8
8000 10421.8
8000 9000
7000 9000