[GRASS-user] Alternative to r.stats to generate % of surface

[Rainer M Krug]

On Tue, Nov 15, 2011 at 1:35 PM, Marcello Gorini <gorini at gmail.com> wrote:

> Hi Helena,
>
> I have come to the same problem and solved it with ugly and very specific
> shell scripts. There is most certainly a better way within GRASS and no
> doubt you can code it much better in Shell, but anyway, this may get you
> going somehow.
>
> Code snippet:
>
> MAP=$1
>
> g.region rast=$MAP
> max_cats=9
> file=true_percentages.txt
> rm $file
>
> tot=$(r.univar $MAP | grep "^n: " | awk '{print $2}')
> r.stats -cn $MAP > stats.txt
>
> cats=1
> while [ $cats -le $max_cats ]; do
>
>     ncat="`head -$cats stats.txt | tail -1 | awk '{print $2}'`"
>     cat="`head -$cats stats.txt | tail -1 | awk '{print $1}'`"
>     perc="`echo $tot $ncat | awk '{printf("%.5f", $2 / $1 * 100);}'`"
>
>     echo $cat $perc >> $file
>
>     cats="$(expr $cats + 1)"
>
> done
>
> I wanted everything in text files, so I generated these stats.txt and
> true_percentages.txt. The idea of the script is to use the actual cell
> count given by r.stats -cn and divide it by the total count given by
> r.univar.
>
> Note that this script is very specific and only work for categories that
> are incremented by 1. In my case, they go from 1 to 9.
>
> How brave I am to publicize such an ugly script, huh? :) The result sums
> up to 1 at least. Just give the name of the categorical map as input.
>
> Hope it helps somehow.
>

What about the -c flag for r.stats? You will get the cell count and can
calculate the percentage yourself.

Rainer


>
> Marcello.
>
>
>
> On Tue, Nov 15, 2011 at 9:36 AM, Helena Herrera <
> helenaherrera1980 at gmail.com> wrote:
>
>> Greetings
>>
>> I want to calculte % of surface in a raster map for each Integer class
>> value. The thing is that I'm, using r.stats but the sum % values is always
>> much more (104 or 102 or 105). Is there any other (more precised) method to
>> calculate this ?
>> THanks
>> Helena
>>
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>>
>
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-- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology,
UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

Tel :       +33 - (0)9 53 10 27 44
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email:      Rainer at krugs.de

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