...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Strategy to calculate the distance between two points.
template<typename CalculationType> class strategy::distance::pythagoras { // ... };
Parameter 
Default 
Description 

typename CalculationType 
void 
numeric type for calculation (e.g. high precision); if void then it is extracted automatically from the coordinate type and (if necessary) promoted to floating point 
Function 
Description 
Parameters 
Returns 

template<typename P1, typename P2> calculation_type< P1, P2 >::type apply(P1 const & p1, P2 const & p2)

applies the distance calculation using pythagoras 
P1 const &: p1: first point P2 const &: p2: second point 
the calculated distance (including taking the square root) 
#include <boost/geometry/strategies/cartesian/distance_pythagoras.hpp>
Note  

Can be used for points with two, three or more dimensions 