[R-sig-Geo] C API for sp classes?

[Wouter Buytaert]

Hi,

I want to write some R functions for calculating hydrological 
catchment characteristics from a DEM (topographic index, overland flow 
delay function etc.).

Looks like using a DEM with SpatialGridDataFrame class as an input is a 
good idea.

Then what is the best way to extract the data matrix from this class to 
pass it on to a .C() function which does the actual calculations?

cheers,

wouter