[STATSGRASS] NULL values and readRAST6

[Roger Bivand]

On Tue, 9 Oct 2007, Roger Bivand wrote:

> On Tue, 9 Oct 2007, Carlos "Guâno" Grohmann wrote:
>
>>  Hi,
>>  Can readRAST6 handle NULL values? How?
>>
>>  I tried NODATA=NULL but it needs a numeric value..
>
> This is passed to r.out.bin, which says:
>
> null=integer
>     Value to write out for null
>     Default: 0
>
> so in fact it has to be an integer - I'll fix the documentation and function 
> (which didn't check what value was assigned to NODATA).

To make this a bit clearer - the raster layer in GRASS has missing values 
set to NULL, but NULL cannot be exported by r.out.bin. So r.out.bin is 
given a NODATA value to assign to NULL cells, which are then read into R, 
and the NODATA valued cells are set to NA. The only need for the value is 
to keep r.out.bin (and r.in.bin) happy, because they do not encode NULL 
directly.

Roger

>
> Roger
>
>>
>>  tks
>>
>>  Carlos
>> 
>> 
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no