[GRASS-user] Multiple labels and r.series

[Hamish]

John wrote:
> I am creating a raster map that essentially summarizes the
> intersection of a series of labeled rasters that each have
> values of either 1 or null (presence/absence data). I am
> using r.series like this to perform the summation across the
> rasters that are all named with a prefix of presence_:
> 
> r.series input="`g.mlist rast
> pattern='presence_*' sep=,`"
> output=presence_sum method=sum --o
> 
> Can anyone think of a way to achieve this summation of
> intersections in a way that will also allow for each cell to
> have a label that concatenates all labels for the respective
> raster maps that are present at that cell? E.g., let's
> say three of the rasters are present at a particular cell,
> and the labels for those rasters are 'raster1',
> 'raster4', and 'raster7'. I would like the
> final map to have a label of 'raster1, raster4,
> raster7'.
> 
> Any and all suggestions are greatly appreciated.


the trick here is to r.reclass 0/1 absence/presence maps to be 0/2^n
before running the sum.  So you then get a sum like 13, which would mean
the 8+2+1 maps were all present, or if the sum was 5 you'd know the 1+4
maps were present for that cell, and not others.


see also r.bitpattern and r.mapcalc bitwise operators.  (sorry I don't
know the proper name/wikipedia link for this technique, I'm not a computer
scientist)


Hamish