1 // Boost.Geometry (aka GGL, Generic Geometry Library)
2 // QuickBook Example
3
4 // Copyright (c) 2011-2012 Barend Gehrels, Amsterdam, the Netherlands.
5
6 // Use, modification and distribution is subject to the Boost Software License,
7 // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
8 // http://www.boost.org/LICENSE_1_0.txt)
9
10 //[for_each_segment_const
11 //` Sample using for_each_segment, using a functor to get the minimum and maximum length of a segment in a linestring
12
13 #include <iostream>
14
15 #include <boost/geometry.hpp>
16 #include <boost/geometry/geometries/linestring.hpp>
17 #include <boost/geometry/geometries/point_xy.hpp>
18
19 #include <boost/assign.hpp>
20
21
22 template <typename Segment>
23 struct gather_segment_statistics
24 {
25 // Remember that if coordinates are integer, the length might be floating point
26 // So use "double" for integers. In other cases, use coordinate type
27 typedef typename boost::geometry::select_most_precise
28 <
29 typename boost::geometry::coordinate_type<Segment>::type,
30 double
31 >::type type;
32
33 type min_length, max_length;
34
35 // Initialize min and max
gather_segment_statisticsgather_segment_statistics36 gather_segment_statistics()
37 : min_length(1e38)
38 , max_length(-1)
39 {}
40
41 // This operator is called for each segment
operator ()gather_segment_statistics42 inline void operator()(Segment const& s)
43 {
44 type length = boost::geometry::length(s);
45 if (length < min_length) min_length = length;
46 if (length > max_length) max_length = length;
47 }
48 };
49
main()50 int main()
51 {
52 // Bring "+=" for a vector into scope
53 using namespace boost::assign;
54
55 // Define a type
56 typedef boost::geometry::model::d2::point_xy<double> point;
57
58 // Declare a linestring
59 boost::geometry::model::linestring<point> polyline;
60
61 // Use Boost.Assign to initialize a linestring
62 polyline += point(0, 0), point(3, 3), point(5, 1), point(6, 2),
63 point(8, 0), point(4, -4), point(1, -1), point(3, 2);
64
65
66 // Declare the gathering class...
67 gather_segment_statistics
68 <
69 boost::geometry::model::referring_segment<point>
70 > functor;
71
72 // ... and use it, the essention.
73 // As also in std::for_each it is a const value, so retrieve it as a return value.
74 functor = boost::geometry::for_each_segment(polyline, functor);
75
76 // Output the results
77 std::cout
78 << "Min segment length: " << functor.min_length << std::endl
79 << "Max segment length: " << functor.max_length << std::endl;
80
81 return 0;
82 }
83
84 //]
85
86
87 //[for_each_segment_const_output
88 /*`
89 Output:
90 [pre
91 Min segment length: 1.41421
92 Max segment length: 5.65685
93 ]
94 */
95 //]
96