How To: Mask and subset a GDB using a polygon mask

Problem/Symptom:
How can I mask a Geosoft GDB using a polygon file (*.PLY) and create a new GDB based on the masked area?

Environment:
Oasis montaj v7.0 and Target v7.0

Resolution
In order to mask a GDB to a polygon you'll need a Geosoft Polygon File (*.PLY). PLY files can be created using numerous methods. For the steps to create a polygon file see FAQ http://www.geosoft.com/support/faq/2008/05/how-to-create-geosoft-polygon.asp

1) Go to Database Tools | Window Data | Window X,Y to Polygon Mask...

2) Select your PLY file, select the area you would like to mask: Outside or Inside. Press OK.

3) At this point all the X,Y coordinates in the GDB that are inside or outside the GDB (depending on the parameter used) will be masked out and replaced in Dummy values (*). Your original channels are backed up and hidden ("_X" and "_Y").

4) To subset the GDB go to Database Tools | Window Data | Subset Database.

5) Select the masked GDB and specify which lines and channels you would like to retain.

6) In the Remove Mask Dummy parameter select "All Dummies".

7) Set the Mask Channel to either the X or Y coordinates channel. Press OK.

NOTE: to remove the mask to the source GDB go to Coordinates | Restore Backup X,Y...