[R-sig-Geo] WriteRaster as Float

[Tom Philippi]

Zebrat--
Loic's example works and generates different sized files on my system.
sessionInfo():
R version 3.1.1 (2014-07-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] raster_2.2-31 rgdal_0.8-16  sp_1.0-15

loaded via a namespace (and not attached):
[1] grid_3.1.1      lattice_0.20-29

If it doesn't work on your system, you might post your sessionInfo().

Try both FLT4S and FLT8S to see if the files have different sizes.  Then,
use GDALinfo() instead of another GIS program to inspect the file, as at
least one GIS program silently converts 4-byte floats to 8-byte doubles.

Other than that, if space is really an issue, your approach of rescaling
and storing as an integer is good. You could divide by 100 and use INT2S if
your temperatures don't get above 327deg K.

Tom 2



On Tue, Nov 11, 2014 at 5:02 AM, Dutrieux, Loic <loic.dutrieux at wur.nl>
wrote:

> Hello Zebrat,
>
> The datatype= argument appears to work well on my system. See if you can
> reproduce the example below:
>
> library(raster)
> r <- raster(system.file("external/test.grd", package="raster"))
>
> writeRaster(r, filename = 'rasterDefault.tif')
> GDALinfo('rasterDefault.tif')
> # By default raster writes to Float64
>
> writeRaster(r, filename = 'rasterFloatSingle.tif', datatype = 'FLT4S')
> GDALinfo('rasterFloatSingle.tif')
> # Float 32
>
> Make sure you do not capitalize the "t" in datatype. datatype is the
> writeRaster() argument and dataType is the function to retrieve data type.
>
> Cheers,
> Loïc
>
> -----Original Message-----
> From: r-sig-geo-bounces at r-project.org [mailto:
> r-sig-geo-bounces at r-project.org] On Behalf Of diamant zebrat
> Sent: Tuesday, November 11, 2014 10:13
> To: Tom Philippi
> Cc: r-sig-geo
> Subject: Re: [R-sig-Geo] WriteRaster as Float
>
> Tom, here goes the details
> The Meteosat images are composed by a matrix of pixels with values of
> surface temperature (or cloud top temperature) in Kelvin, which means
> values like 273.15 I wanted to keep the decimals, thus I need a FLT4S
> 4-byte values. When using
> writeRaster(TTemp,filename=nom,format="GTiff",overwrite=T,datatype="FLT4S")
> I get a file with a size of 7.495.158 bytes.  My particular image is a
> matrix of 1201 lines x 803 columns = 964.403 pixels, with this option
> (datatype="FLT4S") it looks like we get an image that uses
> 8 bytes to store each pixel. In fact, we only need 4 bytes (float) to
> store values like 273.15, thus I am getting images which are too big. Keep
> in mind there is a Meteosat image each 15 min -> 96 a day, etc. These means
> a lot of storage space and I should care about it When opening one of these
> GEOTIFF (LTS4S) with a GIS package, it get an image that is "double
> precision", confirming that the writeRaster is using
> 8 bytes to store each pixel when creating the GEOTIFF with the
> datatype="FLT4S" option The conclusion is that the writeRaster routine is
> not optimized to use the minimum space when writing a geotiff The only
> alternative by now is to multiply my kelvins by ten and save it as an
> integer, this way I only keep one decimal but I get small size files
> writeRaster(TTemp,filename=nom,format="GTiff",overwrite=T,datatype="INT1U")
> However, I still want to keep the real values using 4 byte for each
> pixel...
> thank you
> Zebrat
>
> 2014-11-11 4:32 GMT+00:00 Tom Philippi <tephilippi at gmail.com>:
>
> > Zebrat--
> > Without example code it is difficult to guess what you tried, and what
> > you desire.  By "float" do you mean FLT4S 4-byte values?  If so, try
> > datatype='FLT4S' in your call to writeRaster(), which should be the
> > same as 'Float32' in gdal.  If you mean something else, I guessed
> > wrong, so you might specify a bit more about what you have, want, and
> have tried.
> >
> > Tom 2
> >
> > On Mon, Nov 10, 2014 at 4:38 AM, diamant zebrat
> > <diamant.zebrat at gmail.com>
> > wrote:
> >
> >> Hello,
> >> I am working with R processing Meteosat imagery, which mean a lot of
> >> images every day, and thus a lot of available storage space It looks
> >> like the write raster function of the raster package only allows to
> >> write a Geotiff as integer or as double. I only need float precision,
> >> so I don't need a double as the resulting file gets too big. Is there
> >> any way to store a geotiff with float precision?
> >> Thank you
> >> Zebrat
> >>
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> >>
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> >
>
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