Harmonic mean center of animal locations

Hello list;

I am working with a dataset containing animal locations over time for a large 
number of individuals. I would like to compute a center of activity by 
finding the minimum harmonic mean on a grid overlaying the points of an 
animal (a "standard" to express center of activity in animal ecology). 

I have searched the archives at Jonathan Barons server but have not been able 
to find any package that seem to include such a function.

Do anyone of you know of such a function?

Yours 

Tomas Willebrand
Wildlife Ecologist

PS  I am aware of the dedicated home range programs available but planned to 
do most analysis in R.