[GRASS5] a request to fix v.cutter bug

Michael Barton michael.barton at asu.edu
Wed Mar 10 12:23:30 EST 2004

In helping students with an overlay assignment for my spatial 
technologies class, it became apparent that they were getting strange 
results in trying to clip a set of state-wide soil and geology maps 
with the boundary of a national forest here in Arizona.  A series of 
soil and geology polygons simply were not being clipped--i.e., ignored 
by v.cutter.

Last night I did a lot of exploratory work and finally realized that 
this is due to a known bug in v.cutter. According to the manual...

- - - -
There are a few rare situations that are not currently handled 
correctly. These mostly involve nodes or vertices intersecting exactly 
with lines of the opposite map.  You will know you have hit one of 
these cases because a lot of strange text will start spitting out.

Borders between areas with the same attributes are not dissolved.

There are many places where the code could be optimized greatly.
- - - -

It turns out that the soil and geology polygons stop at the Arizona 
state border. The National Forest boundary also stops at the Arizona 
state border. This apparently is enough of an overlap to cause v.cutter 
to ignore those polygons.

v.cutter is one of the few and very important geoprocessing tools in 
the GRASS vector toolbox. IMHO, it is important for it to work 
correctly. I don't know if this bug is corrected in version 5.7 
(hopefully Radim can enlighten here). However, I want to make a plea 
that it be fixed if possible in both 5.3 and 5.7.


Michael Barton, Professor & Curator
Department of Anthropology
Arizona State University
Tempe, AZ  85287-2402

voice: 480-965-6262; fax: 480-965-7671
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