pdef and interpolation question

[Goodson,Ron [Edm]]

Hi

Perhaps a silly question.

I have some "indexed" data on a polarstereographic grid.  Here is an
example for, lets say, precipitation type:

1 = rain
2 = snow
3 = freezing rain
4 = drizzle
5 = mixed rain-snow

etc.

Since this is on a PS grid, when it comes into GrADS all values are
interpolated.  And, for other reasons, I'm interpolating onto a finer
grid than what is in pdef

As a result, when the original grid data might be a 1 next to a 5 ..
GrADS interpolates this to   1 3 5 (if I use 2x finer resolution)... so
I end up with a not-real "freezing rain" between the rain and mixed
rain-snow.

Is there some sneaky way of telling GrADS to use nearest-neighbour to
interpolate from the original data -- or some other solution I haven't
thought of.  I had thought of regrid (or interp) .. but that might not
work if it happens to grab the new-interpolated value (eg -- the "3" in
the example above.

any thoughts?

tks

ron