[GRASSLIST:5343] Re: 2 prob.: v.proj and overlapping

[Francesco Mirabella]

Hi radim and many thanks for your reply,

no, we did not use the -c option because we thought that polygons should
be cleaned (or maybe not?)

Francesco

On Thu, Jan 13, 2005 at 04:04:53PM +0100, Radim Blazek wrote:
> 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
> >>
> >
> >
> 

-- 
**********************************************
Francesco Mirabella,
Istituto Nazionale di Geofisica e Vulcanologia
Sismologia e Tettonofisica, Roma (Italy)
contact c/o:
Structural Geology and Geophysics
address: University of Perugia,
Dipartimento di Scienze della Terra
Piazza Universita', 1 06100 Perugia (Italy)
tel: ++39.(0)75.585 2651
fax: ++39.(0)75.585 2603
e-mail: mirabell at unipg.it
web: http://www.unipg.it/~mirabell/
**********************************************