[R-sig-Geo] remove first trend from dataset

[Narendran Kodandapani]

Dear all,

I am modeling fire occurrence in a landscape.  I have
150 points spread across the landscape.  However I
notice a 1st order trend when I fit the variogram.  Is
there someway that I can remove this trend from the
data, before I begin the modeling process.

Thanks in advance,

Naren