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.

Polygon Mask Files

• Polygon files are ASCII text files with the default .ply extension.

• Each file contains a list of X,Y coordinates defining one or more polygons.

• Files can include any number of polygons, each with any number of vertices.

• The first and last points of each polygon are assumed to be connected.

File Structure Guidelines:

• Each polygon begins with a line starting with poly # (with p or P in column 1).

• Comment lines begin with / in column 1.

Creating Polygons Interactively

You can also create clip polygon files interactively using the digitising tools available in the Map Tools menu.

Example of a single polygon file: