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

[Johannes Radinger]

On Thu, Sep 4, 2014 at 3:38 PM, Nuno Sá <nunocesardesa at gmail.com> wrote:

> Hello!
>
> Did you try this one?
>
> *r.out.gdal etc nodata*=*'NA'*
>

As mentioned in the manual of r.out.gdal, the no data parameter takes only
float values
and no strings like 'NA'. Without stating as specific value in GRASS, this
nodata-value is
automatically set to e.g. 65535 for DCELL rasters if I remember correctly
and to 255
for BYTE rasters. However, this seems not to be recognized when imported
into R with
the package 'raster'.

/Johannes


>
>
>
> On 4 September 2014 14:27, Johannes Radinger <johannesradinger at gmail.com>
> wrote:
>
>> Hi all,
>>
>> of course it is possible to load the raster maps directly via spgrass6.
>> However, we use this work
>> flow also to exchange some of the maps between different users (e.g. via
>> email) and to permanently
>> store single files (geotiffs that contain the proj information within the
>> file). So, I agree that using spgrass6 would be much more efficient, but
>> I'll stick to exporting to geotiffs and so I need to solve the issues with
>> NA's.
>>
>> /Johannes
>>
>>
>> On Thu, Sep 4, 2014 at 2:31 PM, Thomas Adams <tea3rd at gmail.com> wrote:
>>
>>> 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 <
>>> johannesradinger at 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 at lists.osgeo.org
>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>>>
>>>
>>>
>>>
>>>
>>
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>
>
>
> --
>
> Nuno César de Sá
> +351 91 961 90 37
>
>
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