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Just as a follow up on the idea by Misha. It wouldn't be too
difficult to add a column with a unique integer value to the
polygons. Then, follow Misha's idea, making sure that you use the
newly created column as the raster values. After you have converted
the raster back to a line vector layer, reconnect the attribute
table using the unique integers you created.<br>
<br>
<br>
On 06/03/2012 11:32 AM, Matej Mailing wrote:
<blockquote
cite="mid:CAF44DZdCt4LpuPU10Diyc2MuwtYuWBWj=-3NiqRFUB=Pxx0HOA@mail.gmail.com"
type="cite">
<pre wrap="">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 <a class="moz-txt-link-rfc2396E" href="mailto:micha@arava.co.il"><micha@arava.co.il></a>:
</pre>
<blockquote type="cite">
<pre wrap="">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:
<a class="moz-txt-link-freetext" href="http://www.mail-archive.com/grass-user@lists.osgeo.org/msg01015.html">http://www.mail-archive.com/grass-user@lists.osgeo.org/msg01015.html</a>
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
052-3665918
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