Given a set of locations, this function determines which
locations belongs to the convex hull (or envelope) of the set.
Usage
is_chull(x, y)
isChull(x, y)
Value
A numerical vector of the same length as x and y.
0 indicates that the corresponding location is not part of the convex
hull of the set. Values >0 indicates that the corresponding location
is part of the convex hull, and each value corresponds to the order of the
locations along the convex hull polygon.