Geometry Boost List: Re: [geometry] Units of area (with strategy)

Subject: Re: [geometry] Units of area (with strategy)
From: Fernando Pelliccioni (fpelliccioni_at_[hidden])
Date: 2014-04-14 14:36:57

Any comments?

Thanks!

On Mon, Apr 7, 2014 at 10:28 AM, Fernando Pelliccioni <
fpelliccioni_at_[hidden]> wrote:

> 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.
>