area: calculate area of a geometry

Classes
struct	ggl::area_result< Geometry >
	Meta-function defining return type of area function. More...
class	ggl::concept::AreaStrategy< Strategy >
	Checks strategy for area. More...
struct	ggl::strategy_area< Tag, PointOfSegment >
	Traits class binding an area strategy to a coordinate system. More...
Functions
template<typename Geometry , typename Strategy >
Strategy::return_type	ggl::area (Geometry const &geometry, Strategy const &strategy)
	Calculate area of a geometry using a specified strategy.
template<typename Geometry >
area_result< Geometry >::type	ggl::area (Geometry const &geometry)
	Calculate area of a geometry.

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Detailed Description

Performance

2776 * 1000 area calculations are done in 0.11 seconds (http://trac.osgeo.org/ggl/wiki/Performance#Area1)

Coordinate systems and strategies

Area calculation can be done in Cartesian and in spherical/geographic coordinate systems.

Geometries

The area algorithm calculates the surface area of all geometries having a surface: box, polygon, multi_polygon. The units are the square of the units used for the points defining the surface. If the polygon is defined in meters, the area is in square meters.

Example:

Example showing area calculation of polygons built

{
    ggl::polygon<ggl::point_xy<double> > poly;
    ggl::read_wkt("POLYGON((0 0,0 7,4 2,2 0,0 0))", poly);
    std::cout << "Polygon area is "
        << ggl::area(poly)
        << " square units" << std::endl;

    // Other coordinate system, spherical or geographic (extension)
    ggl::polygon<ggl::point<float, 2, ggl::cs::spherical<ggl::degree> > > sph_poly;
    ggl::read_wkt("POLYGON((0 0,0 45,45 0,0 0))", sph_poly);
    std::cout << "Area is "
        << ggl::area(sph_poly)
        << " on unit sphere " << std::endl;
}

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Function Documentation

template<typename Geometry >

area_result<Geometry>::type ggl::area

(

Geometry const &

geometry

)

Calculate area of a geometry.

The function area returns the area of a polygon, ring, box using the default area-calculation strategy. Strategies are provided for cartesian and spherical coordinate systems The geometries should correct, polygons should be closed and according to the specified orientation (clockwise/counter clockwise)

Parameters:

geometry

a geometry

Returns:

the area

Examples:

03_polygon_example.cpp, c04_a_custom_triangle_example.cpp, c04_b_custom_triangle_example.cpp, x01_qt_example.cpp, x02_numeric_adaptor_example.cpp, and x03_d_soci_example.cpp.

Definition at line 218 of file area.hpp.

template<typename Geometry , typename Strategy >

Strategy::return_type ggl::area	(	Geometry const &	geometry,
		Strategy const &	strategy
	)

Calculate area of a geometry using a specified strategy.

This version of area calculation takes a strategy

Parameters:

	geometry	a geometry
	strategy	the strategy to calculate area. Especially for spherical areas there are some approaches.

Returns:

the area

Definition at line 243 of file area.hpp.