[GRASS-dev] [bug #5485] (grass) v.overly with and operator sometimes produces wrong results

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this bug's URL: http://intevation.de/rt/webrt?serial_num=5485
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Subject: v.overly with and operator sometimes produces wrong results

Platform: GNU/Linux/x86_64
grass obtained from: Trento Italy site
grass binary for platform: Compiled from Sources
GRASS Version: 6.2.0

My name is Andras Fabian, and I use GRASS for a flight simulator project (see more info under http://www.alpilotx.de/documentation.html)
Now I have observed, that in some rare situations, the following command 

"v.overlay -t ainput=pre_extract atype=area alayer=1 binput=biogeo_clip btype=area blayer=1 output=exportAlpine operator=and olayer=1,0,0 --overwrite"

doesn't produce the expected result. To be more exact, it seems as if it turns one of the polygons inside out. To use the above command:
pre_extract is a bunch of - mostly - smaller polygons already cut to a 1x1 degree tile.
biogeo_clip is another large (usually only one) polygon, which was clipped to a 1x1 degree area (so essentially biogeo_clip often has 2-3 flat sides from 1x1 clipping area and the rest is some decently jagged line). 
So what I want with my command is: I would like to have all polygons from pre_extract which are inside biogeo_clip. This almost allays works - but not every time. And my observation is, that this happens in the rare situation when some boundary lines of biogeo_clip exactly overlap with pre_extract.
If you need a test dataset (I suppose), which reproduces this behavior, please let me know. I have put it aside (copied the folders out of /vector subfolder of my working set) - I also saved the "bad result" exportAlpine. And this test is nice, because it is only only some 200Kb in size.

Thank you,

Andras Fabian



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