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
main()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 }
103