[GRASS-user] raster exchange between GRASS and R with nodata
Paulo van Breugel
p.vanbreugel at gmail.com
Thu Sep 4 04:46:08 PDT 2014
You probably have good reasons for your work flow, but just to make sure:
is there a specific reason to export to geotiff first? It seems easier to
import the raster layer directly from GRASS into R using the spgrass6
package (readRAST6)? You can subsequently convert the spatial raster to the
On Thu, Sep 4, 2014 at 11:32 AM, Johannes Radinger <
johannesradinger at gmail.com> wrote:
> 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?
> grass-user mailing list
> grass-user at lists.osgeo.org
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