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// Boost.Geometry (aka GGL, Generic Geometry Library)
// Copyright (c) 1995, 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
// Copyright (c) 1995 Maarten Hilferink, Amsterdam, the Netherlands
// Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
// (geolib/GGL), copyright (c) 1995-2010 Geodan, 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)
#ifndef BOOST_GEOMETRY_STRATEGY_AGNOSTIC_SIMPLIFY_DOUGLAS_PEUCKER_HPP
#define BOOST_GEOMETRY_STRATEGY_AGNOSTIC_SIMPLIFY_DOUGLAS_PEUCKER_HPP
#include <cstddef>
#include <vector>
#include <boost/range.hpp>
#include <boost/geometry/core/cs.hpp>
#include <boost/geometry/strategies/distance.hpp>
//#define GL_DEBUG_DOUGLAS_PEUCKER
#ifdef GL_DEBUG_DOUGLAS_PEUCKER
#include <boost/geometry/io/dsv/write.hpp>
#endif
namespace boost { namespace geometry
{
namespace strategy { namespace simplify
{
#ifndef DOXYGEN_NO_DETAIL
namespace detail
{
/*!
\brief Small wrapper around a point, with an extra member "included"
\details
It has a const-reference to the original point (so no copy here)
\tparam the enclosed point type
*/
template<typename Point>
struct douglas_peucker_point
{
Point const& p;
bool included;
inline douglas_peucker_point(Point const& ap)
: p(ap)
, included(false)
{}
// Necessary for proper compilation
inline douglas_peucker_point<Point> operator=(douglas_peucker_point<Point> const& )
{
return douglas_peucker_point<Point>(*this);
}
};
}
#endif // DOXYGEN_NO_DETAIL
/*!
\brief Implements the simplify algorithm.
\ingroup strategies
\details The douglas_peucker strategy simplifies a linestring, ring or
vector of points using the well-known Douglas-Peucker algorithm.
For the algorithm, see for example:
\see http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm
\see http://www2.dcs.hull.ac.uk/CISRG/projects/Royal-Inst/demos/dp.html
\tparam Point the point type
\tparam PointDistanceStrategy point-segment distance strategy to be used
\note This strategy uses itself a point-segment-distance strategy which
can be specified
\author Barend and Maarten, 1995/1996
\author Barend, revised for Generic Geometry Library, 2008
*/
template
<
typename Point,
typename PointDistanceStrategy
>
class douglas_peucker
{
public :
// See also ticket 5954 https://svn.boost.org/trac/boost/ticket/5954
// Comparable is currently not possible here because it has to be compared to the squared of max_distance, and more.
// For now we have to take the real distance.
typedef PointDistanceStrategy distance_strategy_type;
// typedef typename strategy::distance::services::comparable_type<PointDistanceStrategy>::type distance_strategy_type;
typedef typename strategy::distance::services::return_type<distance_strategy_type>::type return_type;
private :
typedef detail::douglas_peucker_point<Point> dp_point_type;
typedef typename std::vector<dp_point_type>::iterator iterator_type;
static inline void consider(iterator_type begin,
iterator_type end,
return_type const& max_dist, int& n,
distance_strategy_type const& ps_distance_strategy)
{
std::size_t size = end - begin;
// size must be at least 3
// because we want to consider a candidate point in between
if (size <= 2)
{
#ifdef GL_DEBUG_DOUGLAS_PEUCKER
if (begin != end)
{
std::cout << "ignore between " << dsv(begin->p)
<< " and " << dsv((end - 1)->p)
<< " size=" << size << std::endl;
}
std::cout << "return because size=" << size << std::endl;
#endif
return;
}
iterator_type last = end - 1;
#ifdef GL_DEBUG_DOUGLAS_PEUCKER
std::cout << "find between " << dsv(begin->p)
<< " and " << dsv(last->p)
<< " size=" << size << std::endl;
#endif
// Find most far point, compare to the current segment
//geometry::segment<Point const> s(begin->p, last->p);
return_type md(-1.0); // any value < 0
iterator_type candidate;
for(iterator_type it = begin + 1; it != last; ++it)
{
return_type dist = ps_distance_strategy.apply(it->p, begin->p, last->p);
#ifdef GL_DEBUG_DOUGLAS_PEUCKER
std::cout << "consider " << dsv(it->p)
<< " at " << double(dist)
<< ((dist > max_dist) ? " maybe" : " no")
<< std::endl;
#endif
if (dist > md)
{
md = dist;
candidate = it;
}
}
// If a point is found, set the include flag
// and handle segments in between recursively
if (md > max_dist)
{
#ifdef GL_DEBUG_DOUGLAS_PEUCKER
std::cout << "use " << dsv(candidate->p) << std::endl;
#endif
candidate->included = true;
n++;
consider(begin, candidate + 1, max_dist, n, ps_distance_strategy);
consider(candidate, end, max_dist, n, ps_distance_strategy);
}
}
public :
template <typename Range, typename OutputIterator>
static inline OutputIterator apply(Range const& range,
OutputIterator out, double max_distance)
{
distance_strategy_type strategy;
// Copy coordinates, a vector of references to all points
std::vector<dp_point_type> ref_candidates(boost::begin(range),
boost::end(range));
// Include first and last point of line,
// they are always part of the line
int n = 2;
ref_candidates.front().included = true;
ref_candidates.back().included = true;
// Get points, recursively, including them if they are further away
// than the specified distance
typedef typename strategy::distance::services::return_type<distance_strategy_type>::type return_type;
consider(boost::begin(ref_candidates), boost::end(ref_candidates), max_distance, n, strategy);
// Copy included elements to the output
for(typename std::vector<dp_point_type>::const_iterator it
= boost::begin(ref_candidates);
it != boost::end(ref_candidates);
++it)
{
if (it->included)
{
// copy-coordinates does not work because OutputIterator
// does not model Point (??)
//geometry::convert(it->p, *out);
*out = it->p;
out++;
}
}
return out;
}
};
}} // namespace strategy::simplify
}} // namespace boost::geometry
#endif // BOOST_GEOMETRY_STRATEGY_AGNOSTIC_SIMPLIFY_DOUGLAS_PEUCKER_HPP
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