[GRASS-user] Re: Filling Null values in a MODIS image

Hanlie Pretorius hanlie.pretorius at gmail.com
Wed Aug 4 08:13:27 EDT 2010


2010/8/4, Hamish <hamish_b at yahoo.com>:
> Hanlie wrote:
>>  |   Rows:         11957
>>  |   Columns:      6277
> ...
>> I have tried to see the NULLS by displaying everything in
>> white, except for NULLS displayed in red, but I didn't see
>> anything.
>>
>> Does anyone know how I can find out if there are actually
>> NULL value and where they are?
>
> try zooming in. Unless you have a 12000x7000 monitor, some cells will be
> hidden.
>
> extract with r.mapcalc and buffer with r.buffer if they are still hard to
> find.
>

Thanks for all the replies. I first tried finding the NULLS using
r.mapcalc, and it turns out that the NULLS are the cells in the GRASS
region (rectangular), but outside my study region (irregular
geographical border). I was under the misconception that g.region set
to a raster file functions like a mask.

About the r.neighbors procedure, why is it necessary to follow with
r.patch? Surely the result of r.neighbors will be without NULLS? I did
find, though, that r.neighbours resulted in raster with extended
borders compared to the original, which makes sense. One would then
have to clip it again to the study area. Or use a mask of the original
area before running r.patch?

Hanlie


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