[GRASS-user] how to clean vector file after reprojection

Moritz Lennert mlennert at club.worldonline.be
Wed Feb 7 11:18:38 EST 2007

On 07/02/07 15:22, Moritz Lennert wrote:
> On 07/02/07 00:31, Hamish wrote:
>> Moritz Lennert wrote:
>>> I am trying to (inverse) project a vector file from an laea location
>>> to a lat-long location.
>> ..
>>> 2) Which tool (v.clean ?) could I use to solve this ?
>> Yes, try "v.clean tool=snap". Or before reprojection "v.clean
>> tool=break".
> 'break' on the source map does not find any intersections to break.
> 'snap' on target map (v.clean in=nuts2 out=nuts2_snap_0_001 tool=snap 
> thresh=0.001 - which if I calculated correctly should snap anything 
> within a bit more than 100 meters) gives me an even worse result (even 
> less areas are recognized):
> http://moritz.homelinux.org/grass/v_proj_target_after_snap.png
>> My guess is lines are not broken at intersections and reprojected lines
>> no longer exactly touch? (only verticies are projected)
> Yes, that is the problem. I had mistakenly assumed that an end of line 
> automatically is a 'node' and that unclosed lines would show up as 
> one-line nodes. But I see that unclosed ends of lines are not nodes and 
> are, therefore not visible in v.digit...
> But, really strange: looking at the same spot in the source map, the 
> line also is not closed, but is still recognized as an area... ???
> Will have to explore this some more.

Ok, here is what I see in the source location:


And in v.digit:


Zooming in to the area marked by the red circle:


And zooming even further (I'm in the centimeter range there):


The lines are not closed, but they are still recognized as an area.

I assume I must be getting something wrong here, but I don't really 
understand what...

Any hint would be welcome.


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