[GRASS-user] r.mapcalc on RGB composite

[Jarle Pedersen]

Hi again folks. Next noobie question:

I'm trying to use r.mapcalc to set the sea of some landsat imagery to  
null-values in order for me to view my much nicer background. My workflow  
was as follows:

1. r.composite -d -c red="b1" green="b4" blue="b7" levels=32 output="RGB"
2. r.mapcalc "RGB_water=if(dem=0,null(),RGB)"

This does not fill the water with null, rather keeps the original values  
and distorts the colors to yellow/greenish output.

What am I missing?