[GRASS-user] How to find the second largest value in a series of rasters.

[Sylvain Maillard]

what about computing the first largest value, making your categorical map,
and using it as a mask ?

if you mask all cell containing the first largest value, then the second
largest value will become the first largest value of the masked raster
serie ...


my 2 ct

Sylvain



2011/12/10 Marcello Gorini <gorini at gmail.com>

>
>
> Marcello:
>
>
>> > My problem is that I also need to find the *second largest* value and
>> the
>> > corresponding raster number which contains the second largest value.
>> >
>> > I am doing that by iterating over all classes through a shell script,
>> but it
>> > obviously takes much more time than using a simple r.series command.
>> >
>> > Can anyone share any idea on how to accomplish that using r.series or
>> > something similar?
>>
>>
> Glynn:
>
>
>> There isn't an efficient way to do this using existing tools. If you
>> need the efficiency, I suggest adding a "second largest" aggregate to
>> lib/stats (based upon c_max.c and c_maxx.c), and updating r.series to
>> use it.
>>
>>
> Thanks for pointing me the way. I think it is a little beyond my skills,
> but I might give it a try.
>
> Cheers,
> Marcello.
>
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