[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:
http://moritz.homelinux.org/grass/source_display.jpg
And in v.digit:
http://moritz.homelinux.org/grass/source_v_digit1.jpg
Zooming in to the area marked by the red circle:
http://moritz.homelinux.org/grass/source_v_digit2.jpg
And zooming even further (I'm in the centimeter range there):
http://moritz.homelinux.org/grass/source_v_digit3.jpg
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.
Moritz
More information about the grass-user
mailing list