The class Search_traits<NT,Point,CartesianIterator,ConstructCartesianIterator,ConstructMinVertex,ConstructMaxVertex> can be used as a template parameter of the kd tree and the search classes. It is a mere wrapper for the geometric types needed by these classes.
#include <CGAL/Search_traits.h>

 The number type of the coordinates. 

 Point type. 

 An iterator over the coordinates. 

 
A functor with two function operators, which return the begin and past the end iterator for the Cartesian coordinates. The functor for begin has as argument a Point_d. The functor for the past the end iterator, has as argument a Point_d and an int.  

 Functor with operator to construct the vertex with lexicographically smallest coordinates of an object of type Iso_box_d. 

 Functor with operator to construct the vertex with lexicographically largest coordinates of an object of type Iso_box_d. 
Search_traits_2<Kernel>
Search_traits_3<Kernel>
Search_traits_d<Kernel>