[GRASS-user] How to check if a raster has a NULL value

[Moritz Lennert]

On 18/06/19 15:31, Markus Neteler wrote:
> Hi Robert,
> 
> On Tue, Jun 18, 2019 at 1:54 PM Robert Nuske <rsn.mailinglists at gmail.com> wrote:
>>
>> Hi Listers,
>>
>> r.fillnulls exits with an error if the input map has no holes.
>> r.fillnulls one step in a bash script. The processing is stopped if
>> r.fillnulls writes no output because of an error.
>>
>> Thus i would like to check if any holes need to be filled. If this is
>> the case run r.fillnulls and if not just copy input to output map name.
>>
>> Is there a handy command which reports if there are any NULLs in the
>> raster map. The output of the command shall be used in a bash if
>> construction.
> 
> Yes: e.g., r.univar can do that:
> 
> GRASS 7.6.2git (nc_spm_08_grass7):~ >
> 
> g.region raster=boundary_county_500m
> r.univar -g boundary_county_500m
> n=616509
> null_cells=506073
> cells=1122582
> min=0
> max=199
> range=199
> mean=87.1764564669778
> mean_of_abs=87.1764564669778
> stddev=62.4325833627095
> variance=3897.82746534167
> coeff_var=71.6163352961689
> sum=53745070
> 
> Usage in a shell script:
> 
> g.region raster=boundary_county_500m
> eval $(r.univar -g boundary_county_500m)
> echo $null_cells
> 506073
> 

Just watch out that this will not work as expected when you have set a mask:

https://trac.osgeo.org/grass/ticket/3696

Moritz