[GRASS-user] Again on raster statistics

[Luigi Ponti]

Hey there,

Thanks Sören for creating a bug report.

Given that r.stats is not doing the job, would there be another way to 
calculate areas included in subranges of a fp raster? Or also, what is 
the approach to calculating raster areas?

I spent quite some time writing a script that would use the output of 
r.stats and report in a tabular and graphic form, but then I found out 
that r.stats was not reporting correctly itself (see below).

Is simple raster statistics a feature of secondary importance in GRASS, 
i.e. there is other tools that address this primarily.

Thanks and regards,

Luigi



Sören Gebbert wrote:
> Hi,
> i can confirm this bug with the latest grass6.3-cvs version.
>
> Using the test suite mapset i get the following result:
>
> Mapset <testmapset> in Location <TestLocation>
>                                    GRASS 6.3.cvs > g.region -p res=200
>
> GRASS 6.3.cvs > r.mapcalc "stat_test=col()*1.0"
>
> GRASS 6.3.cvs > r.stats -npc input=stat_test nsteps=10
>  100%
> 1-1.9 10  12.50%
> 1.9-2.8 10  12.50%
> 2.8-3.7 10  12.50%
> 3.7-4.6 10  12.50%
> 4.6-5.5 10  12.50%
> 5.5-6.4 10  12.50%
> 6.4-7.3 10  12.50%
> 7.3-8.2 10  12.50%
> 8.2-9.1 10  12.50%
> 9.1-10 10  12.50%
>
> GRASS 6.3.cvs > r.stats -npc input=stat_test nsteps=2
>  100%
> 1-5.5 90 102.27%
> 5.5-10 10  11.36%  <------------ ???
>
>
>
>                                                      GRASS 6.3.cvs > 
> r.stats -npc input=stat_test nsteps=3
>  100%
> 1-4 50  57.47%
> 4-7 40  45.98%
> 7-10 10  11.49%  <------------ ???
>
> I have created a bug report.
>
> Best regards
> Soeren
>
> Luigi Ponti schrieb:
>> Dear list,
>>
>> I take up again a question I posted a couple of week ago with no 
>> aswer. Maybe I am missing something trivial. If so, I would ask you 
>> to please let me know.
>>
>> In order to simulate a strange behaviour I ususally get when 
>> analyzing a raster obtained via v.surf.idw, I have imported the 
>> following sample_raster (into a  Lambert Conformal Conic location 
>> with roughly the extent of Italy) :
>>
>> north: 1957791.56244761
>> south: 764918.56244761
>> east: 754857.88911685
>> west: -279947.29662612
>> rows: 10
>> cols: 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>> 1 2 3 4 5 6 7 8 9 10
>>
>> using the following command:
>>
>> GRASS 6.1.cvs (EurLCC):~ > r.in.ascii -f input=sample_raster.txt 
>> output=sample_raster title="This is a sample raster"
>>
>> Then if I use r.stats with 9 steps I get:
>>
>> GRASS 6.1.cvs (EurLCC):~ > r.stats -nap sample_raster nsteps=9
>> r.stats:  100%
>> 1-2 246878233266.702148  22.23%
>> 2-3 122842792398.404068  11.06%
>> 3-4 124035440868.291550  11.17%
>> 4-5 122842792398.404068  11.06%
>> 5-6 124035440868.291550  11.17%
>> 6-7 122842792398.404068  11.06%
>> 7-8 124035440868.291550  11.17%
>> 8-9 122842792398.404068  11.06%
>> 9-10 124035440868.291550  11.17%
>>
>> But with 2 steps I get:
>>
>> GRASS 6.1.cvs (EurLCC):~ > r.stats -nap sample_raster nsteps=2
>> r.stats:  100%
>> 1-5.5 1110355725439.734619 100.00%
>> 5.5-10 124035440868.291550  11.17%
>>
>> Which does not make a lot of sense to me: there is too much area in 
>> the first half and too little in the second half.
>> Any hints appreciated. Regards,
>>
>> Luigi
>>
>>
>>
>>
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>>
>