Moritz Lennert <mlenn...@club.worldonline.be> writes: > On 23/05/13 10:26, Rainer M Krug wrote: >> >> Hi >> >> I have two raster layers >> >> ,---- >> | dc: CELL, 1, ..., 7, NULL >> | ageClass: CELL, 1,2,3,NULL >> `---- >> >> And I want to create a third one, depending on the value in a lookup >> table. dc corresponds to the row, ageClass to the column, >> >> The lookup table looks as follow: >> >> ,---- >> | seedling young adult >> | dc1 425000 87500 37500 >> | dc2 270000 55000 23500 >> | dc3 127500 26000 11250 >> | dc4 32500 7100 3200 >> | dc5 5550 1220 500 >> | dc6 605 132 55 >> | dc7 56 12 6 >> `---- >> >> Now I want to have something like (using r.mapcalc as an example) >> >> ,---- >> | r.mapcalc expression = "result = lookupTable[col=ageClass, row=dc]" >> `---- >> >> and e.g. for one cell >> >> ,---- >> | ageClass = 3 >> | dc = 5 >> | ==> >> | result = 500 >> `---- >> >> I haven't found anything like this in GRASS. >> >> I could use MASKS and then r.reclass(), or generate dynamically a >> complex if() construct, but both options sound a little bit >> awkward to me. >> >> I am scripting GRASS from R, so there is always the option of doing it >> in R, but there is the issue of reading the data into R and writing it >> back to GRASS, which takes time. As I am doing this in a simulation >> which runs several times, this is not an unimportant issue. >> >> Is there better way of achieving this? > > I don't see a possibility to include the lookup table into r.mapcalc,
Me neither - that was just the easies to show what I want to do.
> but anyway, IIUC, the result you are looking for is not a raster map,
> but a numerical value, or ?
No - the lookup would be for each cell, therefore resulting in a CELL
raster map.
>
> My best first guess is:
>
> r.stats -c in=dc,ageClass
>
> possibly combined with a little awk to do the lookup:
>
> r.stats -c in=dc,ageClass | awk '{if($1==5 && $2==3) print $3}'
>
> Or, if the maps are heavy, feed the data resulting from the r.stats
> call into a new db table and then use sql queries to do the lookup. Or
> feed the results of r.stats into an R dataframe.
Hmm - sounds interesting, but also for other purposes. But as the result
will be a raster map, I don't think this approach is usable here (unless
I can feed the numbers back into a raster map, i.e. the inverse of
r.stats -c)
Rainer
>
> Moritz
--
Rainer M. Krug
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