Sunday, 24 November 2019

pyqgis - where is the v.transects algorithm in qgis?


I am interested in using the v.transects GRASS command. I am however not yet proficient with using GRASS or python in QGIS environment so I would rather do it the old-fashioned way (i.e using the GUI).


When I open my geoprocessing toolbox in QGIS however I don't find it among the listed GRASS functionality. Why is this particular command missing? How can I add it? If not will I have to resort to doing this operation through a command line of some sort (prefer to avoid)





I did end up trying to open the layer in GRASS and running the following command:


v.transects --help


To which I got the following error:



'v.transects' is not recognized as an internal or external command, operable program or batch file.



I know the session environment is OK because when I try to run another command, such as v.buffer --help, I get valid output...


Does the v.transects command even exist? if not why does it appear in the documentation?



Answer



v.transects exists as an add-on (see: https://grass.osgeo.org/grass7/manuals/addons/), so needs to be installed using the command g.extension extension=v.transects in the GRASS GIS console.



If you can't use the console command in QGIS, it's not too hard to use the command in standalone GRASS GIS 7.4.x. The vector layer was loaded in using File > Import Vector Data > Simplified vector import with reprojection. Then after typing v.transects input=busroute6@PERMANENT output=bus_transects transect_spacing=100 --overwrite into the console it produced:


transects


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