Is it normal results, scattered flow lines in a landscape with altimetric amplitude of 50 to 60 meters (see following image). Is it an erratic result?
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Cumprimentos,
Valter Albino - Geógrafo Físico, M.Sc.
Modelação H&H / Riscos ambientais / OT&U
Valter,
Which module did you use to generate flow lines? It wouldn’t be easy to troubleshoot your problem without sample data and detail steps. Are those purple and black lines flow lines?
Best,
Huidae
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Huidae Cho, Ph.D., GISP
GRASS GIS Developer
https://idea.isnew.info
Hi Huidae
Yes, the purple and black lines flow lines. Wondering if using units in “cm”, instead of “m” gives correct results (the online manual sais that, i suppose) in terms of: more number and length of flow lines.
Using r.flow (https://grass.osgeo.org/grass78/manuals/r.flow.html) with the following raster file:
Sorry to moderator (sent 2 files with extra weight)
Huidae Cho <grass4u@gmail.com> escreveu no dia terça, 28/01/2020 à(s) 02:56:
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Cumprimentos,
Valter Albino - Geógrafo Físico, M.Sc.
Modelação H&H / Riscos ambientais / OT&U
Hi,
It’s done, running from GRASS GIS 7.8.2 GUI, in a Windows 64bits OS.
There ares differences when simulating for small areas or bigger areas, with default options.
When testing for bigger areas I wasn’t setting the number of cells bettween flowlines & maximum number of segments per flowline.
Thanks
Valter Albino <valteralbino@gmail.com> escreveu no dia quinta, 30/01/2020 à(s) 09:55:
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Cumprimentos,
Valter Albino - Geógrafo Físico, M.Sc.
Modelação H&H / Riscos ambientais / OT&U
Valter,
The default value for the skip= parameter is max(1, nrows/50, ncols/50), so the density of flowlines depends on the resolution of your elevation map. If you want better defined flowlines, reduce skip (skip=1 for all cells and best, but can be slow). I believe, in your case, those scattered flowlines all start from cells that are “skip” cells apart. I can see those short flowlines in a grid-like manner (distance between starting cells = max(1, nrows/50, ncols/50) by default). So try skip=1 (in UI, Optional => Number of cells between flowlines), then you should get better and continuous flowlines. The better result in one of your emails is a smaller region and a less number of rows and cells, so a smaller skip, I think.
Best,
Huidae
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Huidae Cho, Ph.D., GISP
GRASS GIS Developer
https://idea.isnew.info