[GRASS-user] Calculate average of 3 highest values for a set of raster maps

[Milton Cezar Ribeiro]

Dear all,

Thanks for all replies. I will check it out thoughout the weekend.
Just clarifying something, I need to do the estimations focusing on
each pixels, and not for the full map (I was not that clear before).

Also as my raster maps are very large (~50,000x60,000 pixels) maybe R
(at least on w7) maybe will not handle the seven rasters.

Best wishes

miltinho

2013/3/15, Paulo van Breugel <p.vanbreugel at gmail.com>:
> Sorry, some typo's (but the given code should be ok): set all values <
> 4/7 quantile to null(), not 0, and you want to calculate the average,
> not the sum
>
> On Fri 15 Mar 2013 10:05:51 AM CET, Paulo van Breugel wrote:
>> Hi Miltinho
>>
>> I assume you want the mean of the three highest values for each raster
>> cell? If so, you can do this using another step with r.series
>>
>> 1) If your 7 maps are a1 .. a7:
>>
>> mapcalc "a1 = 1"; r.mapcalc "a2 = 2"; r.mapcalc "a3 = 3"; r.mapcalc
>> "a4 = 4"; r.mapcalc "a5 = 5"; r.mapcalc "a6 = 6"; r.mapcalc "a7 = 7"
>>
>> 2) calculate the 4/7 quantile. Actually, it should be a little bit
>> smaller to make sure you include your 3rd largest layer. In this
>> example below, 0.57 as approximation is fine
>>
>> r.series --overwrite input=a1,a2,a3,a4,a5,a6,a7 quantile=0.57
>> output=res1 method=quantile
>>
>> 2) Next, for all 7 layers, set all values < 4/7 quantile to 0
>>
>> r.mapcalc "b1 = if(a1>res1,a1,null())"
>> r.mapcalc "b2 = if(a2>res1,a2,null())"
>> r.mapcalc "b3 = if(a3>res1,a3,null())"
>> r.mapcalc "b4 = if(a4>res1,a4,null())"
>> r.mapcalc "b5 = if(a5>res1,a5,null())"
>> r.mapcalc "b6 = if(a6>res1,a6,null())"
>> r.mapcalc "b7 = if(a7>res1,a7,null())"
>>
>> 3) Now, calculate the sum of the 7 new layers
>>
>> r.series input=b1,b2,b3,b4,b5,b6,b7 method=average output=res2
>> --overwrite
>>
>> Your output res2 should have a value 6 for all raster cells.
>>
>> Cheers,
>>
>> Paulo
>>
>>
>>
>>
>>
>>
>> On Fri 15 Mar 2013 03:57:35 AM CET, Milton Cezar Ribeiro wrote:
>>> I have a set of 7 raster maps.
>>> I am able to calculate several stats with these mapas using r.series.
>>> Now I need to calculate the mean of the tree highest values of my 7
>>> maps.
>>> Any idea of how can I do that?
>>>
>>> cheers
>


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