On Fri, 5 Dec 2008, [EMAIL PROTECTED] wrote:
Thanks Barry
Hi List,
I am unable to read in a 7.8Gb ascii grid using readAsciiGrid
{maptools}/ read.asciigrid {sp}; R runs out of memory. I have 4Gb ram
and 4Gb swap, so things are getting tight.
I am wondering if anyone has alternative options (preferably with
example) that enable to read in large grids, do some calculations and
save a new grid?
This is another case of posting on r-help and R-sig-geo, leading to the
thread getting confused. I replied on r-help:
https://stat.ethz.ch/pipermail/r-help/2008-December/181686.html
saying that using tiling with rgdal functions - which have a driver for
this data - is the obvious way to go, and that the raster package under
development on R-forge looks very promising for letting users automate the
process of reading rasters in tiles.
See also the relevant thread here:
https://stat.ethz.ch/pipermail/r-sig-geo/2008-November/004486.html
Roger
Depends on what you want to do with it. What's the dimension of the grid in
rows x columns?
-->dimensions 80264x73772 for the largest grid and 28848x47030 for current grid
Firstly, can you convert it to a more efficient format? Ascii Grid files
are generally long lines of numbers, looking like 2.333535 4.457574
2.332336 5.445775 and so on. Maybe 10 characters per grid square. You
might be able to squeeze it to 4 characters per grid square by storing
as raw floating point numbers.
-->yes, depends on what formats R is able to read in
Next, can you just process it serially, one line or grid square at a
time? Do you need to store it all in memory at the same time?
--> I can process serially, I don't need to store it in memory for the
simple math calculations, only for subsequent analysis. But once
calculations are done I can resample/aggregate to higher resolution.
--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [EMAIL PROTECTED]
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