[GRASS-user] Re: Calculating standard error of many maps?

[Glynn Clements]

Moritz Lennert wrote:

> >>> Just one clarification: I would like to calculate these descriptive
> >>> stats for each cell, to obtain "variability maps".
> >>> Rainer
> >>> On Mon, Feb 9, 2009 at 5:57 PM, Rainer M Krug <r.m.krug at gmail.com 
> >>> <mailto:r.m.krug at gmail.com>> wrote:
> >>>> Hi
> >>>>
> >>>> I have 25000 maps, generated by simulation predictions, and I would
> >>>> like to calculate some descriptive stats, like mean, standard
> >>>> deviation, median, quartiles.
> >>>>
> >>>> Is there an easy way of doing this in GRASS?
> >>
> >>
> >> r.series ?
> >>
> >> You will probably have to use xargs to collate that many map names...
> > 
> > Or you can use g.mlist if the names have a common prefix, suffix, etc. 
> > This assumes you want a single map that displays the result of all the 
> > input maps.
> > 
> > E.g.
> > 
> > r.series input="`g.mlist rast pattern='prefix_*' sep=,`" 
> > output=prefix_stddev method=stddev
> 
> Yes, but if I'm not mistaken, this won't work with 25000 maps as it 
> would create a too long command line.

25000 maps will probably also exceed the resource limit for the number of
open descriptors. It's common for user processes to be limited to 1024
descriptors; you need to modify /etc/security/limits.conf to increase the
limit.

-- 
Glynn Clements <glynn at gclements.plus.com>