[GRASS-user] raster exchange between GRASS and R with nodata

Johannes Radinger johannesradinger at gmail.com
Thu Sep 4 02:32:57 PDT 2014


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")
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?

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