Hi all,

I run the "area (with strategy)" example shown on 

http://www.boost.org/doc/libs/1_55_0/libs/geometry/doc/html/geometry/reference/algorithms/area/area_2_with_strategy.html

I'm interested in getting the geodetic area (the second one of the code below)

#include <iostream>

#include <boost/geometry.hpp>

#include <boost/geometry/geometries/polygon.hpp>

#include <boost/geometry/io/wkt/wkt.hpp>

namespace bg = boost::geometry;

int main()

{

   // Calculate the area of a spherical polygon (for latitude: 0 at equator)

   bg::model::polygon<bg::model::point<float, 2, bg::cs::spherical_equatorial<bg::degree> > > sph_poly;

   bg::read_wkt("POLYGON((0 0,0 45,45 0,0 0))", sph_poly);

   double area = bg::area(sph_poly);

   std::cout << "Area: " << area << std::endl;

   return 0;

}

The code above prints out:

Area: 0.339837

In this case, what is the unit of the area?

The documentation states that:

Returns the area on a unit sphere (or another sphere, if specified as such in the constructor of the strategy)

Sorry, but my knowledge of geography is limited.

How can I transform that number to square kilometers, square miles, ...?

Thank you very much.

Regards,

Fernando Pelliccioni.