Q about cross-covariance

I'm interested in examining spatial cross-covariance and would like to display this as a semivariogram with positve and negative lags, yet I'm having dificulty finding the proper code.  Any advice would be greatly appreciated.

Thanks and take care,

Matthew G. Olson
Acadian Forest Ecosystem Research Program
School of Forest Resources
University of Maine, Orono
(207) 581-2763