Roger André wrote:
Hi Martin,
Thanks, that is a exactly the problem. Your page is perfect for
showing the cause and solution.
One question though, since the solution relies on removing polygons
whose areas are less than a minimum threshold, how can we do this
accurately with a global data set? I suppose I could extract each
country, reproject it to a local projection, clean out the bad
polygons, then reproject to lat/lon, and finally patch all of the
separate countries back into single file.
AFAIK, v.clean tool=rmarea calculates area sizes in square meters for
latlon locations, no need to reproject, it should be accurate enough.
Markus M
Roger
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On Sat, Oct 17, 2009 at 12:57 AM, Martin Landa <[email protected]> wrote:
Hi,
2009/10/17 Roger André <[email protected]>:
Tried the v.extract route - it didn't help. The little segments came
sure, because there are no 'lines' - just 'boundaries' and 'centroids'
which constract 'areas'.
along. So I decided to look at the original data and pull one the
polygons from it, to see if I could spot anything strange about it. I
did find something, maybe, maybe one of the experts here can explain
it.
Here is what v.clean reports:
Number of nodes: 55
Number of primitives: 59
Number of points: 0
Number of lines: 0
Number of boundaries: 46
Number of centroids: 13
Number of areas: 13
Number of isles: 9
This country should have 9 areas, which matches the number of isles.
I'm trying to figure out how to remove the extra areas (rmarea thresh
value is tricky), but I wonder if there is a way to make the areas
match the isles?
I was facing probably to the similar problem, it's described here [1].
Sorry it's in Czech, anyway from the commands you can probably
understand what was the problem. I hope it can help you a bit.
Martin
[1]
http://gama.fsv.cvut.cz/wiki/index.php/GRASS_GIS_-_Konzistence_vektorov%C3%BDch_dat
--
Martin Landa <landa.martin gmail.com> * http://gama.fsv.cvut.cz/~landa
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