// Boost.Geometry (aka GGL, Generic Geometry Library) // QuickBook Example // Copyright (c) 2011-2012 Barend Gehrels, Amsterdam, the Netherlands. // Use, modification and distribution is subject to the Boost Software License, // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) //[for_each_segment_const //` Sample using for_each_segment, using a functor to get the minimum and maximum length of a segment in a linestring #include <iostream> #include <boost/geometry.hpp> #include <boost/geometry/geometries/linestring.hpp> #include <boost/geometry/geometries/point_xy.hpp> #include <boost/assign.hpp> template <typename Segment> struct gather_segment_statistics { // Remember that if coordinates are integer, the length might be floating point // So use "double" for integers. In other cases, use coordinate type typedef typename boost::geometry::select_most_precise < typename boost::geometry::coordinate_type<Segment>::type, double >::type type; type min_length, max_length; // Initialize min and max gather_segment_statistics() : min_length(1e38) , max_length(-1) {} // This operator is called for each segment inline void operator()(Segment const& s) { type length = boost::geometry::length(s); if (length < min_length) min_length = length; if (length > max_length) max_length = length; } }; int main() { // Bring "+=" for a vector into scope using namespace boost::assign; // Define a type typedef boost::geometry::model::d2::point_xy<double> point; // Declare a linestring boost::geometry::model::linestring<point> polyline; // Use Boost.Assign to initialize a linestring polyline += point(0, 0), point(3, 3), point(5, 1), point(6, 2), point(8, 0), point(4, -4), point(1, -1), point(3, 2); // Declare the gathering class... gather_segment_statistics < boost::geometry::model::referring_segment<point> > functor; // ... and use it, the essention. // As also in std::for_each it is a const value, so retrieve it as a return value. functor = boost::geometry::for_each_segment(polyline, functor); // Output the results std::cout << "Min segment length: " << functor.min_length << std::endl << "Max segment length: " << functor.max_length << std::endl; return 0; } //] //[for_each_segment_const_output /*` Output: [pre Min segment length: 1.41421 Max segment length: 5.65685 ] */ //]