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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 | } |