[Qgis-user] Centre of the roads from polygons to lines

[Matej Mailing]

Hi,

thanks, will try this one. There are many attributes and losing them
or re-setting them is a very painful process.

I was playing with different plugins and trying to use polygon
centroids and then connecting them with lines, but had problems with
it since it seems that gid values are not different by 1 for
neighbouring nodes and then the point-to-line conversion is wrong.
Perhaps some sort of a functionality to correctly connect polygon
centroids with a line would be most welcome and I am sure it could
also be used in some other cases.

Thanks,
Matej

2012/6/3 Micha Silver <micha at arava.co.il>:
> On 02/06/2012 11:02, Matej Mailing wrote:
>
> Hi,
>
> I have a layer that contains roads in polygons and I need to get
> central lines of the polygons. When I convert directly from polygons
> to lines, I get two lines for each part of the road representing road
> "boundaries" which isn't good.
>
>
> There's a procedure using GRASS that you might choose. It involves
> converting the polygons to a GRASS raster, then running the GRASS module
> r.thin, and then converting back to a vector.
> Here's an old thread that mentions the method:
> http://www.mail-archive.com/grass-user@lists.osgeo.org/msg01015.html
>
> Two difficulties:
> * you have to set the resolution fairly high in order to keep the road's
> shapes, but then the raster might be too large to work with on a large area
> * and you loose the attribute table on the way...
>
> What is the best way to achieve it?
>
> Thanks,
> Matej
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> Micha Silver
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