Creating MASK from vect

Ish Williams ish at
Mon May 4 08:19:40 EDT 1998

>What I would like to have is: a mask, which
>blanks the sea. Since it is not an island, or a lake, it is not a
>closed line, the coastline "enters" at the left (western) end of
>my loacation and "leaves" at the right (easter) end. A simple
>"is-north-of-decision" will fail


I can't think of a way to use a line to mask an area. You might
try heads-up digitizing using r.digit to trace a raster layer
over either the land area or sea. Digitize one and you can mask
either. In masking, you can select either the item digitized or
the "no data" category (everything but the item digitized). Remember
that the no data category is defined at the geographic region that
you use r.digit so if you need to zoom in to r.digit the coast you
will need to recreate the layer (use r.resample) at your default window
to set no data over the geographic extent of your study area.

Ishmael Williams
US Army Corps of Engineers
Ft. Worth District

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