Automatic labelling of polygons

imager at imager at
Mon Sep 14 17:23:20 EDT 1992

Hello Grass Programmers,

I have a very large number of planimetrics covering an area of
interest that are in DXF format. I have stripped out the layers
I am interested in and imported the files into GRASS4.0 using
V.IN.DXF. Directing the files to readable output via V.OUT.ASCII
reveals the files to be made up of L(ines) that consist of a number
of vertices. Display of the data via V.DIGIT reveals them to contain
primarily closed but unlabelled areas (GRASS thinks they are lines

I can convert the lines in the DXF file to area lines (so that they
can be labelled using the "label area" option of V.DIGIT) by using a
macro to edit the V.OUT.ASCII file replacing the "L" entities with "A"
entities and using V.IN.ASCII to bring the edited file back into GRASS.

I would now like to automate the labelling process by writing a program 
to edit the DIG_ATT file to associate each area with (the same)
category value and a point within polygon.


1) How does GRASS check to see if this point actually lies within the
   area? Is the area rasterized and map mathmatics used or a odd/even
   line intersect vector analysis method ? I tried using V.TO.RAST on 
   unlabelled areas but unsuprisingly I get an empty raster
   file as output.

2) Has anyone else already written a program to do this in GRASS?

Thanks in advance,

Tony Gale,
Research Specialist,
City of Austin Electric,
Austin, Tx

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