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89 lines
3.4 KiB
Plaintext
89 lines
3.4 KiB
Plaintext
[/==============================================================================
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Copyright (c) 1995-2010 Barend Gehrels, Geodan, Amsterdam, the Netherlands.
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Copyright (c) 2008-2010 Bruno Lalande, Paris, France.
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Copyright (c) 2009-2010 Mateusz Loskot (mateusz@loskot.net), London, UK
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Use, modification and distribution is subject to the Boost Software License,
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Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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===============================================================================/]
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[section area]
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['TODO: type and function names to be inter-linked --mloskot]
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[heading Description]
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Calculate area of a geometry.
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The area algorithm calculates the surface area of all geometries having a surface, namely
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box, polygon, ring, multipolygon. The units are the square of the units used for the points
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defining the surface. If subject geometry is defined in meters, then area is calculated
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in square meters.
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The area calculation can be done in all three common coordinate systems, Cartesian, Spherical
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and Geographic as well.
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[heading Synopsis]
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namespace boost { namespace geometry {
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template<typename Geometry>
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typename area_result<Geometry>::type area(Geometry const &geometry)
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template<typename Geometry, typename Strategy>
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Strategy::return_type area(Geometry const &geometry, Strategy const &strategy)
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template<typename Geometry>
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typename area_result<Geometry>::type area(Geometry const &geometry)
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}}
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[table Template Parameters
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[[Parameter] [Requirement] [Description]]
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[[`Geometry`] [Models of one of geometry __concepts__] []]
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[[`Strategy`] [Models of AreaStrategy] []]
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]
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[table Parameters
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[[Parameter] [Requirement] [Description]]
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[[`geometry`] [Shall form a valid geometry]
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[Polygon should be closed and according to specified orientation (clockwise or counter-clockwise)]]
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[[`strategy`] [['TODO]]
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[Specifies algorithm of area calculation, especially useful for spherical areas where number
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of approaches are possible]]
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]
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[table Expression Semantics
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[[Expression] [Return Type] [Description]]
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[[__area__(geometry);] [`area_result<Geometry>::type`]
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[Calculates area of polygon, ring, box using default area strategy provided for __wiki_cs_cartesian__ and __wiki_cs_spherical__]]
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[[__area__(geometry,strategy);] [`Strategy::return_type`]
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[Calculates area of polygon, ring, box using specified area strategy]]
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]
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[heading Complexity]
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[table
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[[Notation] [Name] [Notes]]
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[[`O(n)`] [__wiki_complex_linear__] []]
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]
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Benchmark example: calculation of `2776 * 1000` areas done in 0.11 seconds (see [@http://trac.osgeo.org/ggl/wiki/Performance Performance] earticle on the Wiki).
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[heading Header]
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#include <boost/geometry/algorithms/area.hpp>
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[heading Example]
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using namespace boost::geometry;
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polygon<boost::geometry::point_xy<double> > poly;
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read_wkt("POLYGON((0 0,0 7,4 2,2 0,0 0))", poly);
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std::cout << "Polygon area is " << area(poly) << " square units" << std::endl;
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// Other coordinate system, spherical or geographic (extension)
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polygon<point<float, 2, cs::spherical<degree> > > sph_poly;
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read_wkt("POLYGON((0 0,0 45,45 0,0 0))", sph_poly);
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std::cout << "Area is " << area(sph_poly) << " on unit sphere " << std::endl;
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[endsect] [/ end of section area] |