[R-sig-Geo] properly using function aggregate(raster)

[Robert J. Hijmans]

Dear Guillaume,

This probably happened because the aggregate function tests if the
output raster can be stored in memory. This is a mistake as it should
do the test for the input raster (which is, in this case, 16 times
larger). I have just fixed that. For now, you can use this (otherwise
*not* recommended (or necessary), as it slows things down) option, to
force processing the file in chunks :

setOptions(todisk=TRUE)
wam<-aggregate(wam, fact=4, fun=mean, expand=FALSE,
filename="wam_ag4", progress='tcltk')
setOptions(todisk=FALSE)

Robert

On Mon, May 17, 2010 at 10:15 AM, Guillaume Blanchet
<gblanchet.list at gmail.com> wrote:
> Hi !
>
> I recently started to use the raster package to play with a file that I
> consider fairly big. Since file size is subjective, following is the
> summary output R gives of the data I am working with :
>
>  > wam
> class       : RasterLayer
> filename    : w001001.adf
> nrow        : 14143
> ncol        : 11733
> ncell       : 165939819
> min value   : 0
> max value   : 36.3769
> projection  : +proj=utm +zone=11 +ellps=GRS80 +datum=NAD83 +units=m
> +no_defs +towgs84=0,0,0
> xmin        : 410133
> xmax        : 421866
> ymin        : 6287971
> ymax        : 6302114
> xres        : 1
> yres        : 1
>
> I would like to aggregate the information of that RasterLayer. I tried
> to use the function aggregate() without any real success. Following is
> the code line I use to perform that procedure and the error message I get:
>
>  > wam<-aggregate(wam, fact=4, fun=mean, expand=FALSE, filename="wam_ag4")
>
> Erreur : impossible d'allouer un vecteur de taille 633.0 Mo (A loose
> translation would be : "Error: allocating a vector of 633.0 Mb in size
> is impossible")
> De plus : Messages d'avis :
> 1: In .local(x, ...) :
>   Reached total allocation of 3061Mb: see help(memory.size)
> 2: In .local(x, ...) :
>   Reached total allocation of 3061Mb: see help(memory.size)
> 3: In .local(x, ...) :
>   Reached total allocation of 3061Mb: see help(memory.size)
> 4: In .local(x, ...) :
>   Reached total allocation of 3061Mb: see help(memory.size)
>
> I understood while reading help files and various posting that the
> raster package can handle files larger than the RAM memory of the
> computer. The computer I am using has 3Gb of RAM and the file I want to
> read is only 633 Mb. I suppose there something I am not doing right.
>
> Any help would be much appreciated !
>
> Thank you in advance !
>
> Guillaume Blanchet
>
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>
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