[GRASS-user] Trying to reclassify raster using non-linear functions in GRASS

[Vaclav Petras]

On Fri, Nov 8, 2013 at 8:14 AM, Glynn Clements <glynn at gclements.plus.com>wrote:

>
> Gabriel Zorello Laporta wrote:
>
> > I am using ArcInfo Workstation and Grid in order to to produce Gaussian
> > functions of elevation from a DEM with minimum value at 800m, as follow:
> >
> > elev_x800 = elev90 - 800
> > elev_x800sq = pow(elev_x800, 2)
> > elev_x800sqn = -1 * elev_x800sq
> > elev_x800sqnd = elev_x800sqn / 500000
> > elev_x800exp = exp(elev_x800sqnd)
> > elev_x800gaus = elev_x800exp * 0.000798
> > elev_x800gi = (elev_x800gaus * -11330) + 10.044
> >
> > I was wondering how to apply that in GRASS (because I want to move
> towards
> > Open Software). Can you help me?
>
> You should be able to use those exact same expressions in r.mapcalc,
> e.g.
>
>         r.mapcalc <<EOF
>         elev_x800 = elev90 - 800
>         elev_x800sq = pow(elev_x800, 2)
>         elev_x800sqn = -1 * elev_x800sq
>         elev_x800sqnd = elev_x800sqn / 500000
>         elev_x800exp = exp(elev_x800sqnd)
>         elev_x800gaus = elev_x800exp * 0.000798
>         elev_x800gi = (elev_x800gaus * -11330) + 10.044
>         EOF
>
> The above will write out each step as a map; if you only need the
> final result (elev_x800gi), you can omit all of the intermediate steps
> and use e.g.:
>
>         r.mapcalc "elev_x800gi = (exp(-((elev90 - 800)^2) / 500000) *
> 0.000798 * -11330) + 10.044"
>
> Or, if you want to keep the expressions in the above form but only
> want the last one written out as a map, use eval(), e.g.:
>
>         r.mapcalc <<EOF
>         eval(elev_x800 = elev90 - 800,\
>              elev_x800sq = pow(elev_x800, 2),\
>              elev_x800sqn = -1 * elev_x800sq,\
>              elev_x800sqnd = elev_x800sqn / 500000,\
>              elev_x800exp = exp(elev_x800sqnd),\
>              elev_x800gaus = elev_x800exp * 0.000798)
>         elev_x800gi = (elev_x800gaus * -11330) + 10.044
>         EOF
>
> This is an interesting feature. I added this example to r.mapcalc manual
in G7 [r58173].

It is in Notes section. I was not sure where to put it and it is only a
dummy example. Maybe, it would be helpful to have this "Gaussian functions"
example in examples but I don't know what it is, so I don't want to write
about it.

It is bit unfortunate that this example does not work in mapcalc in wxGUI.
I'm not sure if it is a serious issue and where to mention it
(manual/gui/...).

Vaclav

https://trac.osgeo.org/grass/changeset/58173

PS: MarkusN, I've tried to do it I passive voice this time.

--
> Glynn Clements <glynn at gclements.plus.com>
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