[GRASS-user] can the grass calculate the area of different color for a image(tiff or other?)

[Micha Silver]

Moritz Lennert wrote:

> On 17/06/09 14:06, maven apache wrote:
>> I got a.green a.red a.blue and a.alpha four raster,then follow the 
>> advise from this list I composite the three map g b r to a new 
>> raster:outss
>> then I run the commond r.stats -a input=outss at PERMANENT 
>> <mailto:input=outss at PERMANENT> fs=space nv=* nsteps=255
>> got the following output
>>  
>> 0 429847.542397
>> 9321 212745757.083273
>> 26425 4430667.032198
>> 31744 5444337463.194785
>> 32736 35683640.857434
>> 32767 92624.052023
>>  
>> I wonder what do the first number in each line respent? And the 
>> second number in each respent the area?
>
>
> RTFM ;-)
>
> The first number is the category number, i.e. the different categories 
> (in your case colors) present in your map.
> The second number gives the area statistics which are given in units 
> of square meters.
>
> Moritz
> ________
And if you want to improve the output, then two steps:
First use r.category to give a label to each category like so:
(assuming the first is black)
echo "0:Black" | r.category outss rules=-
(note the '-' which means "read from stdin")
Next use r.report like so:
r.report outss unit=k
(gives a table with the cat value, the label and area in sqkm)

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