Forgot to mention: On Wed, Sep 2, 2020 at 6:28 PM Markus Neteler <nete...@osgeo.org> wrote: > On Wed, Sep 2, 2020 at 1:27 PM Ken Mankoff <mank...@gmail.com> wrote: > > > > Hi GRASS list, > > > > I'd like to detect "narrow" features in GRASS. The attached screenshot > > shows some basins (thick) and streams (thin) and some regions (hatched). > > These regions are spurious because the basin is narrow here. I'd like to > > estimate narrowness with an algorithm. > > > > I've looked into r.grow.distance r.distance and v.distance but haven't been > > able to imagine a solution yet. Can anyone on this list suggest something? > > Perhaps the compact measure of > > https://grass.osgeo.org/grass78/manuals/v.to.db.html > --> compact: compactness of an area, calculated as compactness = > perimeter / (2 * sqrt(PI * area)) > > could help here?
Related to compactness I found https://www.azavea.com/blog/2016/07/11/measuring-district-compactness-postgis/ and roughly digitized the shapes presented therein and moved them into "North Carolina" sample data area with r.region. The results of v.to.db/compactness are completely different, likely because it is a different measure from the Polsby-Popper measure used there. However, maybe a dataset to play with... Best Markus -- Markus Neteler, PhD https://www.mundialis.de - free data with free software https://grass.osgeo.org https://courses.neteler.org/blog
shapes_for_compactness_NC.gpkg
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