Hi Stefan, +1 for that suggestion. There might be a few variants / other directional measures that could be included with a 'method' argument like real surface area.
Cheers, Steve On Wed, Jan 25, 2017 at 3:32 PM, Blumentrath, Stefan < stefan.blumentr...@nina.no> wrote: > Hi Steven, > > > > And many thanks for clarification and contrasting results in detail… > > And sorry for throwing the question at the list without having checked > that (I just scanned the module code). > > > > I noticed the difference in the references referred to in both modules. > From scanning the code they seemed to do the same thing, but now I see > that the main difference is probably that r.vector.ruggedness uses slope > directly for weighting vector strength, while r.roughness.vector uses the > “inverted” slope / colatitude angle (90 – slope). Apart from that both > modules look quite similar (as are the names) in terms of what they do to > the DEM. > > > > So, there might still be a point of consolidating them into one module > which offers both the “Sappington et al. 2007 metric” and the “Hobson 1972 > metric”… > > > > Just a thought… > > > > Kind regards, > > Stefan > > > > > > *From:* Steven Pawley [mailto:dr.stevenpaw...@gmail.com] > *Sent:* onsdag 25. januar 2017 21.18 > *To:* Luca Delucchi <lucadel...@gmail.com> > *Cc:* Blumentrath, Stefan <stefan.blumentr...@nina.no>; > carlos.grohm...@gmail.com; grass-dev@lists.osgeo.org > *Subject:* Re: [GRASS-dev] [GRASS GIS] #3269: r.roughness.vector: bug in > rescale formula > > > > Hi, > > > > There seems to be some difference in the calculation between these two > add-ons. Apologies for any duplication, but in the way of explanation I > wrote the parallelized r.vector.ruggedness because I needed to calculate > the VRM measure in a hurry and was confused about the results from > r.roughness.vector. > > > > The result from r.vector.ruggedness is identical (apart from how slope and > aspect are calculated) to the result from the Sappington et al. 2007 paper > and the Sappington-authored script in ArcGIS (see attached derived from the > nc_spm_08 grass dataset). The form of the calculation is slightly different > (but the end result is the same) because I average rather than sum the x,y, > and z rasters to avoid a strong edge effect because AFAIK r.mapcalc doesn't > have an automated method of dealing with bordering nulls (hence the > averaging workaround). The r.vector.ruggedness results are also the same as > how SAGA GIS calculates this metric, and it is this version of the 'VRM' > metric that has been used extensively in the literature over the past few > years. > > > > r.roughness.vector appears to produce a very different result (see > attached). Perhaps this represents an alternative implementation, but the > main difference lies in how the DEM is decomposed into its x,y, and z > components. > > > > So if the add-ons are to be merged then perhaps this needs to be resolved? > > > > Steve > > > > On Tue, Jan 24, 2017 at 3:43 PM, Luca Delucchi <lucadel...@gmail.com> > wrote: > > On 24 January 2017 at 09:55, Blumentrath, Stefan > <stefan.blumentr...@nina.no> wrote: > > Hi, > > > > Hi, > > > Another related question: There are now two AddOns for this purpose: > > > > r.roughness.vector (last changed 2 years ago) > > > > and from 2016: r.vector.ruggedness > > > > Both basically calculate the same metric(s), though they have their > differences and both have their pros: > > r.roughness.vector offers more advanced options (esp. useful for multi > scale application) > > r.vector.ruggedness uses parallelization > > > > Having two modules for one task / metric, which are not conceptually > different is a bit confusing... > > IMHO both should be merged into one, keeping the strength of each of > them... > > > > +1 for merging... this could be a work for the next code sprint > > > Other thoughts? > > > > Cheers > > Stefan > > > > -- > ciao > Luca > > www.lucadelu.org > _______________________________________________ > grass-dev mailing list > grass-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-dev > > >
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