[Qgis-user] Middle line of a river basin

[Thayer Young]

 I don't know of a way to do it in QGIS, but you can use the ST_ApproximateMedialAxis function in PostGIS. Note your PostGIS needs to be compiled with the SFCGAL library. Note that not all PostGIS installers will include SFCGAL. 
Also you may still need to clean up the data further, my understanding is that this is a very difficult problem and an area of research in computer science. 
https://postgis.net/docs/ST_ApproximateMedialAxis.html

-Thayer

    On Tuesday, October 12, 2021, 05:46:01 AM EDT, qgis-user-request at lists.osgeo.org <qgis-user-request at lists.osgeo.org> wrote:------------------------------

Message: 3
Date: Mon, 11 Oct 2021 18:49:23 -0600
From: Allan L?pez <allosa01 at gmail.com>
To: Qgis-user at lists.osgeo.org
Subject: [Qgis-user] Middle line of a river basin
Message-ID:
    <CABOeUQ-jaGXtfoZZsN=44nn8xTFVXixF_jgxwvndQ3J6_fJnFg at mail.gmail.com>
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Dear All,

I need to automatically delineate the middle line of a river basin/valley
bounded by a Shp and then to construct lines perpendicular to it spaced at
will. All this to get the
Transverse topographic symmetry factor (T).

My appreciation in advance,

Allan L?pez
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