[Qgis-user] Sextante select polygons by their shapes

[Victor Olaya]

Michal

there is not a tool for that, but you can easily create a workflow in
SEXTANTE to get the result you need

1) calculate the perimeter of each polygon with the "add geometry
columns" algorithm

2) calculate a circularity measure with the field calculator (see
here: http://en.wikipedia.org/wiki/Shape_factor_(image_analysis_and_microscopy)
 )

3) select based on it.

If you want to select a given percentage of the "most-circular"
shapes, you can normalize the circularity measure with the field
calculator as well, so you can easily select the N most circular ones
or the x% of them.

Regards



2013/3/26 Michał Bełcik <belcikmichal at gmail.com>:
> Hi everyone
>
> Is there any tool in Sextante to select polygons by their shapes? For
> example, I would only like to select those that are more or less circular,
> and not thin and extended in length. Is there any way to select them by
> their width to length ratio or anything similar?
>
> All the best
>
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-user
>