96 lines
3.3 KiB
Plaintext
96 lines
3.3 KiB
Plaintext
[/============================================================================
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Boost.Geometry (aka GGL, Generic Geometry Library)
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Copyright (c) 2009-2012 Barend Gehrels, Amsterdam, the Netherlands.
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Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
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Copyright (c) 2009-2012 Bruno Lalande, Paris, France.
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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:quickstart Quick Start]
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This Quick Start section shows some of the features of __boost_geometry__
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in the form of annotated, relatively simple, code snippets.
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The code below assumes that `boost/geometry.hpp` is included, and that `namespace
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boost::geometry` is used. __boost_geometry__ is header only, so including
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headerfiles is enough. There is no linking with any library necessary.
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[quickstart_include]
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[h3 Cartesian]
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It is possible to use only a small part of the library. For example: the
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distance between two points is a common use case. __boost_geometry__ can calculate
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it from various types. Using one of its own types:
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[quickstart_distance]
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If the right headers are included and the types are bound to a coordinate
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system, various other types can be used as points: plain C array's, __boost_array__'s,
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__boost_tuple__'s, __boost_fusion__ imported structs, your own classes...
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Registering and using a C array:
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[quickstart_register_c_array]
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[quickstart_distance_c_array]
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Another often used algorithm is point-in-polygon. It is implemented in __boost_geometry__
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under the name `within`. We show its usage here checking a __boost_tuple__ (as a point)
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located within a polygon, filled with C Array point pairs.
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But it is first necessary to register a __boost_tuple__, like the C array:
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[quickstart_register_boost_tuple]
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[quickstart_point_in_polygon]
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We can calculate the area of a polygon:
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[quickstart_area]
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By the nature of a template library, it is possible to mix point types.
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We calculate distance again, now using a C array point and a __boost_tuple__ point:
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[quickstart_distance_mixed]
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The snippets listed above generate the following output:
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[pre
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Distance p1-p2 is: 1.41421
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Distance a-b is: 2.23607
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Point p is in polygon? true
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Area: 3.015
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Distance a-p is: 2.87924
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]
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[h3 Non-Cartesian]
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It is also possible to use non-Cartesian points. For example: points on a sphere.
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When then an algorithm such as distance is used the library "inspects" that it
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is handling spherical points and calculates the distance over the sphere,
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instead of applying the Pythagorean theorem.
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[note __boost_geometry__ supports a geographical coordinate system, but that is
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in an extension and not released in the current Boost release.]
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We approximate the Earth as a sphere and calculate the distance between Amsterdam
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and Paris:
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[quick_start_spherical]
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It writes: [pre Distance in miles: 267.02]
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[h3 Adapted structs]
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Finally an example from a totally different domain: developing window-based
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applications, for example using QtWidgets. As soon as Qt classes are registered
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in __boost_geometry__ we can use them. We can, for example, check if two
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rectangles overlap and if so, move the second one to another place:
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[quickstart_qt]
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[h3 More]
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In the reference many more examples can be found.
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[endsect]
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