How To: Mask and window a grid using a polygon mask

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

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

Resolution
In order to mask a Grid 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 Grid and Image > Utilities > Window a Grid using a Polygon File.

2) Select the Input Grid file and give the output grid file a name.

3) Select your PLY file (see the link above), and select the area you would like to mask: Outside or Inside. Press OK.

Note: In order to create a windowed grid, you want to mask the area Outside the polygon.

4) This creates a new windowed grid.

5) To window or clip a grid to specified X, Y, or Z data limits (rectangular), use Grid and Image > Utilities > Window a Grid.

The masking polygon may be defined either in a clockwise or counter-clockwise sense. There may be more than one polygon defined in a polygon file. The masking process will mask the grid against ALL polygons defined in the file. When masking outside the polygon, grid points that lie on a polygon edge are not dummied. When masking inside the polygon, points on a polygon edge are dummied.

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