ceph/src/boost/libs/geometry/doc/src/examples/algorithms/for_each_segment_const.cpp

   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
  36     gather_segment_statistics()
  37         : min_length(1e38)
  38         , max_length(-1)
  39     {}
  40
  41     // This operator is called for each segment
  42     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
  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 //]