[GRASS-user] compositing rasters

[Dave Roberts]

Tyler,

     Well, that's simply brilliant.  I knew it should be easy.  Plus, 
when I tested it I found out my rasters weren't truly mutually exclusive 
after all, as some cells = 3.  This is apparently an artifact of 
v.to.rast polygon boundary issues but it's a pretty small problem.

     Nonetheless, I have begun work on the r.update function I mentioned 
in my last post.  It has general utility (e.g. fixing the non-exclusive 
problems I just mentioned) and seems easy enough as a crude hack.  If it 
shows general utility I'll post it and see if someone with GRASS coding 
skills wants to take it up in C with the API.

Thanks Tyler!

On 01/01/2014 09:56 AM, Tyler Smith wrote:
> Dave Roberts <dvrbts at ecology.msu.montana.edu> wrote:
>
>     Colleagues,
>
>     I know this must be easy, but I haven't found it.
>
>     Suppose I have three grids (a, b, and c) where each grid is 0 or 1,
>     and the 1s are mutually exclusive.  I want a new grid where if grid
>     a=1 then newgrid = 1; if grid b=1 then new grid = 2; if grid c=1 then
>     newgrid = 3.
>
>     Something like  r.mapcalc "new=if(a,1) || if(b,2) || if(c,3)"
>
>     seems like it ought to work but I can't seem to use multiple input file
>     that way.
>
>     Thanks in advance for any help, Dave
>
>
> What about
>
> r.mapcalc new=a + b*2 + c*3
>
> If the maps are mutually exclusive, only one of the three will be
> non-zero for each cell.
>
> Tyler

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David W. Roberts                                     office 406-994-4548
Professor and Head                                      FAX 406-994-3190
Department of Ecology                         email droberts at montana.edu
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