SEEK

There is a desire to be able to clip GARP environment layers based on a Convex
Hull region surrounding an existing set of species occurence locations. THere is
a desire not only to calculate a ConvexHull, but also to specify some region on
the outside of the CH that species might exampd into.
It is assumed that the CH is some vector description (polygon?) that can be used
to mask the raster environment layers input to GARP