[GRASS-dev] using slope/aspect functions inside our module

[Carlos "Guâno" Grohmann]

Interesting.
Why r.slope.aspect uses

dx = ... / (4 * ewres);

while r.shaded.relief uses

dx = ... / (8 * ewres);

??

BTW there is a typo in r.shaded.relief in line 137 ("Nap"):

g.message -e  "Nap <$elev> not found."


Carlos


On 7/4/07, Glynn Clements <glynn at gclements.plus.com> wrote:
>
> Yann wrote:
>
> > In a given chain processing module (DN->high-level product) in development,
> > there is a need of calculating slope and aspect, i would like to use the
> > existing code as a library or something to the similar effect.
> >
> > Anyone could explain if it is possible and how it could be possible?
>
> It isn't practical to use code from a module in a library.
>
> Even if it was, calculating slope/aspect is so trivial that it's
> easier to just write it from scratch than to extract the code from
> r.slope.aspect.
>
> FWIW, the calculation which r.slope.aspect uses is essentially:
>
>         dx = ((c1 + 2*c4 + c7) - (c3 + 2*c6 + c9)) / (4 * ewres);
>         dy = ((c7 + 2*c8 + c9) - (c1 + 2*c2 + c3)) / (4 * nsres);
>         key = dx*dx + dy*dy;
>         slp_in_perc = 100*sqrt(key);
>         slp_in_deg = atan(sqrt(key)) * radians_to_degrees;
>         aspect = (atan2(dy,dx)/degrees_to_radians);
>
> where the cells are labelled:
>
>         c1 c2 c3
>         c4 c5 c6
>         c7 c8 c9
>
> --
> Glynn Clements <glynn at gclements.plus.com>
>
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> http://grass.itc.it/mailman/listinfo/grass-dev
>


-- 
+-----------------------------------------------------------+
              Carlos Henrique Grohmann - Guano
  Visiting Researcher at Kingston University London - UK
  Geologist M.Sc  - Doctorate Student at IGc-USP - Brazil
Linux User #89721  - carlos dot grohmann at gmail dot com
+-----------------------------------------------------------+
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