[GRASS-user] Classify basins as "narrow"

[Ken Mankoff]

Hi Markus,

On 2020-09-02 at 09:28 -07, Markus Neteler <neteler at osgeo.org> wrote...
> On Wed, Sep 2, 2020 at 1:27 PM Ken Mankoff <mankoff at gmail.com> wrote:
>> 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.
>
> 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?

Thank you for sharing this. I did not see your email when I wrote my reply with my solution. I need spatial variance in the result, not a single measure per-basin (that is, I want to be able to say "look out for results in this part of the basin, it is narrow, but don't worry elsewhere in this basin").

However, elsewhere on this project I need to know something about neighboring basins, and was looking into that. Your suggestion to read the v.to.db page led me to the "sides" option there, which I think solves that issue.

Thank you!

  -k.