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

[Moritz Lennert]

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.

Moritz