* Helmut Kudrnovsky <hel...@web.de> [2019-02-02 08:17:03 -0700]:
NikosAlexandris wrote
Dear "elevation" experts,
I am looking for ways to upscale a 5m resolution elevation model. The
upscaled models will be subjected to a series of trials using
`r.watershed`. Derivative products will be inputs for soil erosion
modelling.
In our wiki page about Interpolation [0], `r.resamp.stats` [1] is
presented as the only tool to resample a raster map to a coarser grid.
However, `r.resamp.rst` [2] also performs resampling to a lower
resolution.
[0] https://grasswiki.osgeo.org/wiki/Interpolation
[1] https://grass.osgeo.org/grass76/manuals/r.resamp.stats.html
[2] https://grass.osgeo.org/grass76/manuals/r.resamp.rst.html
While the target is to somewhat maintain "geomorphometric consistency"
across the different (coarser) scales, which tool is recommended?
For `r.resamp.stats`, would you recommend a resampling method other than
'average'?
Thank you, Nikos
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you can see
https://grass.osgeo.org/grass74/manuals/addons/r.valley.bottom.html
"[....]The MRVBF index assesses the flatness and lowness of terrain over
multiple scales and DEM resolutions[...]"
how it's there.
Ahoy Helmut,
resampling takes place through the helper function `refine()` [0]. Then,
if I understand it right, you use 'average' (for `r.resamp.stats`) only when
upscaling [1].
[0]
https://trac.osgeo.org/grass/browser/grass-addons/grass7/raster/r.valley.bottom/r.valley.bottom.py#L391
[1]
https://trac.osgeo.org/grass/browser/grass-addons/grass7/raster/r.valley.bottom/r.valley.bottom.py#L595.
You use 'bilinear' when downscaling (the slope and the "percentile" that
is), right? [2, 3]. The "percentile" (number of lower elevation points /
total number of points in surrounding region), is part of the algorithm.
[2]
https://trac.osgeo.org/grass/browser/grass-addons/grass7/raster/r.valley.bottom/r.valley.bottom.py#L591
[3]
https://trac.osgeo.org/grass/browser/grass-addons/grass7/raster/r.valley.bottom/r.valley.bottom.py#L601
Can we use this tool to say "look, our resampled elevation maps are
similar"? But then, I'd need to run this for each resampled map and
compare the outputs (say MRVBF or/and MRRTF)?
Or is it simpler what you suggest?
Nikos
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