[GRASS-user] r.mapcalc map arithmetic and raster data types

[Patton, Eric]

I've differenced two raster maps that are both type DCELL; (this in itself is strange, as I don't have any recollection of generating the input maps at this level of precision; FCELL would have been fine) the resulting raster map was an INT map whose cell values were all exactly zero. Why is this so? Is this because r.mapcalc math on two DCELL maps can't be represented on 32-bit architecture?  

I've tried using r.mapcalc's float function to convert the input maps to FCELL values, but the output remains DCELL:

# The input raster's vitals
>r.info -rst BOF_ALLBATHY_Nov22_2007_10m
min=-278.542236
max=4.744175
nsres=10
ewres=10
datatype=DCELL

r.mapcalc BOF_ALLBATHY_Nov22_2007_10m_Float = 'BOF_ALLBATHY_Nov22_2007_10m'
 100%

# Output raster's vitals
r.info -rst BOF_ALLBATHY_Nov22_2007_10m_Float
min=-88.874466
max=-26.577181
nsres=10
ewres=10
datatype=DCELL

# The change in the raster range is because I've zoomed into a smaller subset of 
the original data to speed up calculations.

Shouldn't r.mapcalc's float function have produced an FCELL map?

~ Eric.