The function ch_nswe_point finds the four extreme points of a given set of input points using a linear scan of the input points. That is, it determines the points with maximal $$y, minimal $$y, minimal $$x, and maximal $$x coordinates.
#include <CGAL/ch_selected_extreme_points_2.h>
 

 
traverses the range [first,beyond). After execution, the value of n is an iterator in the range such that *n $$ _{yx} *it for all iterators it in the range. Similarly, for s, w, and e the inequalities *s $$ _{yx} *it, *w $$ _{xy} *it, and *e $$ _{xy} *it hold for all iterators it in the range. 
The default traits class Default_traits is the kernel in which the type ForwardIterator::value_type is defined.
CGAL::ch_e_point
CGAL::ch_n_point
CGAL::ch_ns_point
CGAL::ch_s_point
CGAL::ch_w_point
CGAL::ch_we_point