Reading jpeg and tiff
On Fri, 27 Apr 2007, ONKELINX, Thierry wrote:
Dear useRs,
I'm trying to read jpeg and GeoTiff with readGDAL() (rgdal package). The
jpeg is about 5.6 MB in size, has 3063 rows and 4870 columns and has 3
bands. The tiff is 3.7 MB, has 15750 rows and 12600 colums and 1 band. I
can't import neither of them in R due to a lack of memory. Although I've
set the memory limit to the max (memory.limit(size =
round(memory.limit()/1048576.0, 2))). I'm running R 2.4.1 on a Win Xp
machine with 2 GB RAM.
So far I managed to read in the data but a lower resolution, which I
don't want. Any suggestions on a more efficient way to import these
files. Solutions based on Spatial-classes are prefered.
Here is the code I'm using now.
library(rgdal)
memory.limit(size = round(memory.limit()/1048576.0, 2))
info <- GDALinfo("d://ferraris0894.jpg")
readGDAL("d://ferraris0894.jpg", output.dim = round(c(info[["rows"]],
info[["columns"]]) / 2))
The usual way to handle things is in tiles, using GDALopen() and then accessing subsets in turn from the handle. The same can be done with readGDAL(). Remember that tiffs and jpegs are highly compressed, your tiff will be 800MB for integer or 1.6GB for double mode, while the underlying data are almost certainly 0-255 byte values. If you would like to look, the code in gdal-bindings.cpp pre-dates R's raw classes, but since raw doesn't really have operators, you'd end up casting at least to integer. The real question is what you want to do with the data, and whether you can tile it or adapt the flow of analysis. Roger
sessionInfo() R version 2.4.1 (2006-12-18) i386-pc-mingw32 locale: LC_COLLATE=Dutch_Belgium.1252;LC_CTYPE=Dutch_Belgium.1252;LC_MONETARY=Du tch_Belgium.1252;LC_NUMERIC=C;LC_TIME=Dutch_Belgium.1252 attached base packages: [1] "stats" "graphics" "grDevices" "utils" "datasets" "tcltk" [7] "methods" "base" other attached packages: rgdal sp svIO R2HTML svMisc svSocket svIDE "0.5-8" "0.9-13" "0.9-5" "1.58" "0.9-5" "0.9-5" "0.9-5" Thanks, Thierry ------------------------------------------------------------------------ ---- ir. Thierry Onkelinx Instituut voor natuur- en bosonderzoek / Reseach Institute for Nature and Forest Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, methodology and quality assurance Gaverstraat 4 9500 Geraardsbergen Belgium tel. + 32 54/436 185 Thierry.Onkelinx at inbo.be www.inbo.be Do not put your faith in what statistics say until you have carefully considered what they do not say. ~William W. Watt A statistical analysis, properly conducted, is a delicate dissection of uncertainties, a surgery of suppositions. ~M.J.Moroney
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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: Roger.Bivand at nhh.no