[Qgis-user] centroid

[John C. Tull]

On Feb 16, 2009, at 9:34 PM, ambrish dhaka wrote:

> Thanks! John,
> Actually the two are independent queries, but yes I have been  
> interchangeably trying to create polygons in QGIS and GRASS as well.  
> The problem is that in QGIS when there is commoon boundary between  
> two polygons it is actually double. And, if by chance it is  
> disturbed then you never get the original one, besides why there  
> should be this doubling. This does not happen in arcgis.
> ANy solutions to this?
> regards,
> Ambrish
>

I'm afraid this is something that will have to be addressed in future  
development efforts. I agree that this is problematic as dashed lines  
often appear as solid due to being drawn more than once. Perhaps the  
new symbology work will not have shared boundaries overlap, but I am  
not certain if this has been brought up before. There are others who  
would know better than I.

Regards,
John

> > CC: qgis-user at lists.osgeo.org; giohappy at gmail.com
> > From: john.tull at wildnevada.org
> > To: ambijat at hotmail.com
> > Subject: Re: [Qgis-user] centroid
> > Date: Mon, 16 Feb 2009 18:24:36 -0800
> >
> > I think this is the solution you wanted. You were not clear about
> > doing this with the GRASS Tools plugin in qgis, but your followup
> > question on watershed creation seems to indicate that is your  
> desire.
> >
> > To aid in getting useful recommendations, please be more specific in
> > your requests, including the operating system, version of qgis, and
> > anything else that is pertinent, like using GRASS Tools.
> >
> > Regards,
> > John
> >
> > On Feb 16, 2009, at 2:47 PM, G. Allegri wrote:
> >
> > >> is there any autocomplete
> > >> for a line to create polygons from lines to adjacent polygon.
> > >
> > > In GRASS you can use:
> > >
> > > # v.type in=input_lines out=output_boundary type=line,boundary
> > >
> > > and then add centroids to the created boundaries with something  
> like
> > > (I'm going with memory, you should check the command syntax):
> > >
> > > # v.centroids input=output_boundary output=output_polygon  
> option=add
> > >
> > > Obviously you have to check the topology results at then end.  
> It's up
> > > to you to have a consitent starting line vector (closed arcs,  
> islands,
> > > etc.), otherwise you will have to correct it with the usual  
> commands
> > > (v.clean, vlbuild, etc.)
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> >
>
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