Mask Channel to Polygon

Use the Database Tools > Window Data > Mask Channel to Polygon menu option (POLYMASK GX) to mask a channel in the database against one or more polygons defined in a polygon file. Data points inside or outside the polygons will be dummied in the reference channel.

Mask Channel to Polygon dialog options

Input X channel	Input X Channel Name. Script Parameter: POLYMASK.INX
Input Y channel	Input Y Channel Name. Script Parameter: POLYMASK.INY
Polygon file	Input polygon file. Script Parameter: POLYMASK.FILE
Channel to mask	Channel to mask. If the channel does not exist, it is created with the class type "MASK". Script Parameter: POLYMASK.CHAN
Dummy inside or outside	"INSIDE" data inside polygons is dummied. "OUTSIDE" data outside polygons is dummied. Script Parameter: POLYMASK.DUMMY

Application Notes

If the channel to be masked does not exist, it is created as a "MASK" class channel with an integer type and initialized to "1" before the masking is performed.

If the channel exists already, then no initialization is performed. Instead, the masking operation will reset only those values which fall inside or outside the polygon (as defined above) to dummy, and the remaining values remain unchanged.

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: