[GRASS-PSC] GRASS add-on sharing and write access

[Anna Petrášová]

Hi Nagy,

On Sat, Dec 16, 2017 at 2:06 PM, Nagy Edmond <nagy.edmond.eno at gmail.com> wrote:
> Hi Anna,
>
> Thank you for pointing that out. It always computes one way between two
> points indeed, but there is something that I should bring to light.
>
> While I was initially computing least-cost paths with r.drain using r.walk
> outputs as inputs I noticed a possible problem. I ran two parallel tests
> with the same two points. In the first one, A was the starting position,
> while B the stop position. In the second one, B was the start point and A
> the stop point. In r.walk, the results were anisotropic indeed, both the
> walking cost and the movement direction raster outputs turned out different,
> as it would have been expected. But the r.drain module sadly did not
> generate different least-cost paths, despite using different inputs. I have
> also checked this more than once, just to be sure of it.
>
> At one point I have also come across an article (Gietl et al. 2008 - link
> below) where the authors discuss and compare l.c.p. results obtained with
> different GIS (including GRASS), and they had also experienced some problem
> with the module (page 4), but I am not sure if it's the same I'm having. In
> any case, if nothing can be done about it, then I will mention the
> limitation in the documentation.
>

you are right that r.drain seem to create the same path from A to B
and back, there are some slight differences, but that can be just
numerical cause. I am not sure why is that, if my expectation that the
path for that DEM should be different is incorrect, or there is some
problem in the algorithm. I don't think what the paper refers to is
the same thing though.

Anna

> All the best,
> Nagy Edmond
>
> article -
> http://proceedings.caaconference.org/paper/106_gietl_et_al_caa2007/
>
>
>
> --
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