raster analysis using real locations? deficiency in mapcalc??

Happy New Year everyone.

I want to manipulate a raster map layer where I
apply a polynomial transformation, in which the
coefficients of the polynomial are a (simple) function
of real location. r.mapcalc only appears to know about
relative locations (using the neighbourhood operator).
I can imagine a gruesome technique involving r.stats
and some awk scripts, but there must be a better way.
Can anyone make a suggestion?

Simon Cox
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      __ L Dr Simon Cox
   ,~' L_|\ VIEPS Department of Earth Sciences,
,-' \ Monash University, Clayton Vic 3168
( \ Australia
\ ___ / Phone +61 3 905 5762
L,~' "\_x/ Fax +61 3 905 5062
           u simon@artemis.earth.monash.edu.au
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