Johannes, If you want to read your file into R, there is no need to export your map from GRASS to do this. Simply install and use the R contributed package 'spgrass6' (spgrass6 has R dependencies that need to be installed first); it works wonderfully:
Within GRASS, at the GRASS terminal prompt... > library(spgrass6) Loading required package: sp Loading required package: XML GRASS GIS interface loaded with GRASS version: GRASS 7.0.0beta3 (2014) and location: ohrfc_mpe > dat<-readRAST6("xmrg0101200306z") > image(dat) This is far more efficient. Tom On Thu, Sep 4, 2014 at 5:32 AM, Johannes Radinger < johannesradin...@gmail.com> wrote: > Hi, > > I want to export a raster map (FCELL) from GRASS70 to the geotiff format > using r.out.gdal and to import it later on in R. The map contains many no > data values. > > Here some details about the raster: > Type of Map: raster Number of Categories: 0 > Data Type: FCELL > Rows: 750 > Columns: 750 > Total Cells: 562500 > total null and non-null cells: 15105636 > total null cells: 15105047 > > So when I export the map, r.out.gdal reports: "Input raster map contains > cells with NULL-value (no-data). The value -nan will be used to represent > no-data values in the input map. You can specify a nodata value with the > nodata option." > > When I subsequently try to import the geotiff into R (using the package > 'Raster') the nodata values are not recognised as NA's: > > a <- raster("*.tif") > summary(a) > Min. 0.5294496 > 1st Qu. 0.7171210 > Median 0.7871540 > 3rd Qu. 1.1581826 > Max. 1.5494517 > NA's 0.0000000 > > So I am wondering if I need to set any specific parameter during the > export (r.out.gdal) or import (raster()). > > As I am not only exporting FCELL (Float32) raster but also multiple > (N=500) other rasters to R I would be interested in a solution also for > DCELL (Float64). Of course I can export all of as Float64 as the file size > should not be a problem. > > Any suggestions or experiences of handling NA's during raster exchange > between GRASS and R? > > /Johannes > > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user >
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