ceph/src/boost/libs/geometry/example/c10_custom_cs_example.cpp

   1 // Boost.Geometry (aka GGL, Generic Geometry Library)
   2
   3 // Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
   4 // Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
   5 // Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
   6
   7 // Use, modification and distribution is subject to the Boost Software License,
   8 // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   9 // http://www.boost.org/LICENSE_1_0.txt)
  10 //
  11 // Example: Custom coordinate system example
  12
  13 #include <iostream>
  14
  15 #include <boost/geometry/geometry.hpp>
  16
  17 // 1: declare a coordinate system. For example for Mars
  18 //    Like for the Earth, we let the use choose between degrees or radians
  19 //    (Unfortunately, in real life Mars has two coordinate systems:
  20 //     http://planetarynames.wr.usgs.gov/Page/MARS/system)
  21 template<typename DegreeOrRadian>
  22 struct martian
  23 {
  24     typedef DegreeOrRadian units;
  25 };
  26
  27 // 2: give it also a family
  28 struct martian_tag;
  29
  30 // 3: register to which coordinate system family it belongs to
  31 //    this must be done in namespace boost::geometry::traits
  32 namespace boost { namespace geometry { namespace traits
  33 {
  34
  35 template <typename DegreeOrRadian>
  36 struct cs_tag<martian<DegreeOrRadian> >
  37 {
  38     typedef martian_tag type;
  39 };
  40
  41 }}} // namespaces
  42
  43
  44 // NOTE: if the next steps would not be here,
  45 // compiling a distance function call with martian coordinates
  46 // would result in a MPL assertion
  47
  48 // 4: so register a distance strategy as its default strategy
  49 namespace boost { namespace geometry { namespace strategy { namespace distance { namespace services
  50 {
  51
  52 template <typename Point1, typename Point2>
  53 struct default_strategy<point_tag, point_tag, Point1, Point2, martian_tag, martian_tag>
  54 {
  55     typedef haversine<double> type;
  56 };
  57
  58 }}}}} // namespaces
  59
  60 // 5: not worked out. To implement a specific distance strategy for Mars,
  61 //    e.g. with the Mars radius given by default,
  62 //    you will have to implement (/register) several other metafunctions:
  63 //      tag, return_type, similar_type, comparable_type,
  64 //    and structs:
  65 //      get_similar, get_comparable, result_from_distance
  66 //   See e.g. .../boost/geometry/extensions/gis/geographic/strategies/andoyer.hpp
  67
  68 int main()
  69 {
  70     typedef boost::geometry::model::point
  71         <
  72             double, 2, martian<boost::geometry::degree>
  73         > mars_point;
  74
  75     // Declare two points
  76     // (Source: http://nssdc.gsfc.nasa.gov/planetary/mars_mileage_guide.html)
  77     // (Other sources: Wiki and Google give slightly different coordinates, resulting
  78     //  in other distance, 20 km off)
  79     mars_point viking1(-48.23, 22.54); // Viking 1 landing site in Chryse Planitia
  80     mars_point pathfinder(-33.55, 19.33); // Pathfinder landing site in Ares Vallis
  81
  82     double d = boost::geometry::distance(viking1, pathfinder); // Distance in radians on unit-sphere
  83
  84     // Using the Mars mean radius
  85     // (Source: http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html)
  86     std::cout << "Distance between Viking1 and Pathfinder landing sites: "
  87         << d * 3389.5 << " km" << std::endl;
  88
  89     // We would get 832.616 here, same order as the 835 (rounded on 5 km) listed
  90     // on the mentioned site
  91
  92 #ifdef OPTIONALLY_ELLIPSOIDAL
  93     // Optionally the distance can be calculated more accurate by an Ellipsoidal approach,
  94     // giving 834.444 km
  95     d = boost::geometry::distance(viking1, pathfinder,
  96         boost::geometry::strategy::distance::andoyer<mars_point>
  97             (boost::geometry::srs::spheroid<double>(3396.2, 3376.2)));
  98     std::cout << "Ellipsoidal distance: " << d << " km" << std::endl;
  99 #endif
 100
 101     return 0;
 102 }