[R-sig-Geo] Measure the distance/home range along terrain surface

[Zulima Tablado Almela]

Hello all,

I have two questions:

1)Given two coordinates on a digital elevation model (DEM), I would like 
to measure the actual distance traveled between the two locations, 
assuming a straight line route. Does anyone know the function(if there 
exists) to do that in R?

2)How can I calculate or correct the home range size taking into account 
the variations in elevation (DEM) within it?

Thank you so much in advance, any suggestion will be very much appreciated,

Zulima