strategies/cartesian/buffer_join_miter.hpp

0001 // Boost.Geometry (aka GGL, Generic Geometry Library)
0002
0003 // Copyright (c) 2012-2014 Barend Gehrels, Amsterdam, the Netherlands.
0004
0005 // Use, modification and distribution is subject to the Boost Software License,
0006 // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
0007 // http://www.boost.org/LICENSE_1_0.txt)
0008
0009 #ifndef BOOST_GEOMETRY_STRATEGIES_CARTESIAN_BUFFER_JOIN_MITER_HPP
0010 #define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_BUFFER_JOIN_MITER_HPP
0011
0012 #include <boost/geometry/core/assert.hpp>
0013 #include <boost/geometry/core/cs.hpp>
0014 #include <boost/geometry/policies/compare.hpp>
0015 #include <boost/geometry/util/math.hpp>
0016 #include <boost/geometry/util/select_most_precise.hpp>
0017
0018 #include <boost/geometry/strategies/buffer.hpp>
0019
0020
0021 namespace boost { namespace geometry
0022 {
0023
0024 namespace strategy { namespace buffer
0025 {
0026
0027 /*!
0028 \brief Let the buffer create sharp corners
0029 \ingroup strategies
0030 \details This strategy can be used as JoinStrategy for the buffer algorithm.
0031     It creates a sharp corners around each convex vertex. It can be applied
0032     for (multi)linestrings and (multi)polygons.
0033     If corners are sharp by themselves, the miters might become very long. Therefore
0034     there is a limit (miter_limit), in terms of the used distance, which limits
0035     their length. The miter is not changed to a bevel form (as done in some
0036     other software), it is just adapted to the specified miter_limit but keeps
0037     its miter form.
0038     If the buffer distance is 5.0, and the miter limit is 2.0, generated points
0039     will be located at a distance of at most 10.0 (2*5) units.
0040     This strategy is only applicable for Cartesian coordinate systems.
0041
0042 \qbk{
0043 [heading Example]
0044 [buffer_join_miter]
0045 [heading Output]
0046 [$img/strategies/buffer_join_miter.png]
0047 [heading See also]
0048 \* [link geometry.reference.algorithms.buffer.buffer_7_with_strategies buffer (with strategies)]
0049 \* [link geometry.reference.strategies.strategy_buffer_join_round join_round]
0050 }
0051  */
0052 class join_miter
0053 {
0054 public:
0055
0056     //! \brief Constructs the strategy
0057     //! \param miter_limit The miter limit, to avoid excessively long miters around sharp corners
0058     explicit inline join_miter(double miter_limit = 5.0)
0059         : m_miter_limit(valid_limit(miter_limit))
0060     {}
0061
0062 #ifndef DOXYGEN_SHOULD_SKIP_THIS
0063     //! Fills output_range with a sharp shape around a vertex
0064     template <typename Point, typename DistanceType, typename RangeOut>
0065     inline bool apply(Point const& ip, Point const& vertex,
0066                 Point const& perp1, Point const& perp2,
0067                 DistanceType const& buffer_distance,
0068                 RangeOut& range_out) const
0069     {
0070         geometry::equal_to<Point> equals;
0071         if (equals(ip, vertex))
0072         {
0073             return false;
0074         }
0075         if (equals(perp1, perp2))
0076         {
0077             return false;
0078         }
0079
0080         using promoted_type = typename geometry::select_most_precise
0081         <
0082             coordinate_type_t<Point>,
0083             double
0084         >::type;
0085
0086         Point p = ip;
0087
0088         // Check the distance ip-vertex (= miter distance)
0089         // (We calculate it manually (not using Pythagoras strategy) to reuse
0090         //  dx and dy)
0091         promoted_type const dx = get<0>(p) - get<0>(vertex);
0092         promoted_type const dy = get<1>(p) - get<1>(vertex);
0093
0094         promoted_type const distance = geometry::math::sqrt(dx * dx + dy * dy);
0095
0096         promoted_type const max_distance
0097             = m_miter_limit * geometry::math::abs(buffer_distance);
0098
0099         if (distance > max_distance)
0100         {
0101             BOOST_GEOMETRY_ASSERT(distance != 0.0);
0102
0103             promoted_type const proportion = max_distance / distance;
0104             set<0>(p, get<0>(vertex) + dx * proportion);
0105             set<1>(p, get<1>(vertex) + dy * proportion);
0106         }
0107
0108         range_out.push_back(perp1);
0109         range_out.push_back(p);
0110         range_out.push_back(perp2);
0111         return true;
0112     }
0113
0114     template <typename NumericType>
0115     inline NumericType max_distance(NumericType const& distance) const
0116     {
0117         return distance * m_miter_limit;
0118     }
0119
0120 #endif // DOXYGEN_SHOULD_SKIP_THIS
0121
0122 private :
0123     double valid_limit(double miter_limit) const
0124     {
0125         if (miter_limit < 1.0)
0126         {
0127             // It should always exceed the buffer distance
0128             miter_limit = 1.0;
0129         }
0130         return miter_limit;
0131     }
0132
0133     double m_miter_limit;
0134 };
0135
0136 }} // namespace strategy::buffer
0137
0138
0139 }} // namespace boost::geometry
0140
0141 #endif // BOOST_GEOMETRY_STRATEGIES_CARTESIAN_BUFFER_JOIN_MITER_HPP