[GRASSLIST:5342] Re: 2 prob.: v.proj and overlapping

Radim Blazek blazek at itc.it
Thu Jan 13 10:04:53 EST 2005


Have you used v.in.ogr -c?

Radim

Francesco Mirabella wrote:
> Hi Radim and all,
> 
> I am currently working with ivan regarding the topic of this message:
> 
> Actually, we had some problems when reprojecting from UTM to
> Gauss-Boaga as Ivan wrote before. The original map was Corinne landcover
> 2000 (.shp).
> The problem first arised after reprojection to Gauss-Boaga so we decided
> to go back to the originally imported map into UTM (corinne landcover
> 2000 is utm).
> 
> The original UTM corinne was displayed well also when queried 
> (d.what.vect), but when looking into it in detail with v.digit we found
> that a lot of boundaries were duplicated. It means that each vertex snapped
> over another of the same boundary, closing where the boundary start (the
> start and the end of the boundary is the same!!! and also all the other
> nodes).
> This brings to the creation of a lot of doubled areas and their centroids are positionated exaclty over the double boundary...
> 
> To try to solve this, we decided to try to delete the double areas and
> tried v.clean tool=rmarea thresh=es.1(meter) in order to have the small double areas removed.
> 
> Now the problem is that v.clean was still removing areas on the map but the process is still running after 15 hours work on a pentium 4 processor, 512 Mb ram!
> 
> many thanks for your help
> 
> Francesco
> 
> 
> 
> On Thu, Jan 13, 2005 at 12:09:23PM +0100, Radim Blazek wrote:
> 
>>ivan marchesini wrote:
>>
>>>Dear users...
>>>I've got two problems using grass57....
>>>
>>>the first one:
>>>I've an area vector map in UTM ED50 system (imported from a shp map)...
>>>is a complex map, with a lot of boundary segments and a lot of
>>>centroids... but it is quite correct because all the areas seems to
>>>answer correcly to v.what.vect... and all boundaries are two areas
>>>boundaries... according to v.digit..
>>>I've projected it on gauss-boaga roma40 system (an italian system) using
>>>v.proj...
>>>now only few areas are preserved...(in the gauss-boaga system I mean)
>>>and there are a lot of not correct boundaries (no area or 1 area... as
>>>v.digit explain...). Consequently, also areas are not respected ....
>>>can you explain me the reason of this behaviour... and how to solve the
>>>problem??? thank you
>>
>>That is interesting. In theory, reprojection could maybe corrupt the 
>>topology, but it is not probable for UTM and Gauss-Boaga on a small 
>>area. Could you send me a small example (use v.in.region and v.select)
>>including both PROJ_INFO?
>>
>>Radim
>>
> 
> 




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