[GRASS-dev] [GRASS GIS] #3269: r.roughness.vector: bug in rescale formula

[Steven Pawley]

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.Blumentrath at 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.stevenpawley at gmail.com]
> *Sent:* onsdag 25. januar 2017 21.18
> *To:* Luca Delucchi <lucadeluge at gmail.com>
> *Cc:* Blumentrath, Stefan <Stefan.Blumentrath at nina.no>;
> carlos.grohmann at gmail.com; grass-dev at 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 <lucadeluge at gmail.com>
> wrote:
>
> On 24 January 2017 at 09:55, Blumentrath, Stefan
> <Stefan.Blumentrath at 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
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>
>
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