123 lines
4.4 KiB
C++
123 lines
4.4 KiB
C++
#include "engine/douglas_peucker.hpp"
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#include "util/coordinate.hpp"
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#include "util/coordinate_calculation.hpp"
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#include "util/integer_range.hpp"
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#include "util/web_mercator.hpp"
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#include <boost/assert.hpp>
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#include <algorithm>
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#include <cmath>
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#include <iterator>
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#include <stack>
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#include <utility>
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namespace osrm::engine
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{
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// Normed to the thresholds table
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std::uint64_t fastPerpendicularDistance(const util::FloatCoordinate &projected_start,
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const util::FloatCoordinate &projected_target,
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const util::FloatCoordinate &projected)
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{
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util::FloatCoordinate projected_point_on_segment;
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std::tie(std::ignore, projected_point_on_segment) =
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util::coordinate_calculation::projectPointOnSegment(
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projected_start, projected_target, projected);
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auto squared_distance = util::coordinate_calculation::squaredEuclideanDistance(
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projected, projected_point_on_segment);
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return squared_distance;
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}
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std::vector<util::Coordinate> douglasPeucker(std::vector<util::Coordinate>::const_iterator begin,
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std::vector<util::Coordinate>::const_iterator end,
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const unsigned zoom_level)
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{
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BOOST_ASSERT_MSG(zoom_level < detail::DOUGLAS_PEUCKER_THRESHOLDS_SIZE,
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"unsupported zoom level");
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const std::size_t size = std::distance(begin, end);
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if (size < 2)
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{
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return {};
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}
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std::vector<util::FloatCoordinate> projected_coordinates(size);
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std::transform(begin,
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end,
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projected_coordinates.begin(),
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[](const util::Coordinate coord)
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{ return util::web_mercator::fromWGS84(coord); });
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std::vector<bool> is_necessary(size, false);
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BOOST_ASSERT(is_necessary.size() >= 2);
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is_necessary.front() = true;
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is_necessary.back() = true;
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using GeometryRange = std::pair<std::size_t, std::size_t>;
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std::stack<GeometryRange> recursion_stack;
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recursion_stack.emplace(0UL, size - 1);
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// mark locations as 'necessary' by divide-and-conquer
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while (!recursion_stack.empty())
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{
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// pop next element
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const GeometryRange pair = recursion_stack.top();
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recursion_stack.pop();
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// sanity checks
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BOOST_ASSERT_MSG(is_necessary[pair.first], "left border must be necessary");
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BOOST_ASSERT_MSG(is_necessary[pair.second], "right border must be necessary");
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BOOST_ASSERT_MSG(pair.second < size, "right border outside of geometry");
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BOOST_ASSERT_MSG(pair.first <= pair.second, "left border on the wrong side");
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std::uint64_t max_distance = 0;
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auto farthest_entry_index = pair.second;
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// sweep over range to find the maximum
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for (auto idx = pair.first + 1; idx != pair.second; ++idx)
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{
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using namespace util::coordinate_calculation;
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const auto distance = fastPerpendicularDistance(projected_coordinates[pair.first],
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projected_coordinates[pair.second],
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projected_coordinates[idx]);
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// found new feasible maximum?
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if (distance > max_distance &&
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distance > detail::DOUGLAS_PEUCKER_THRESHOLDS[zoom_level])
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{
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farthest_entry_index = idx;
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max_distance = distance;
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}
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}
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// check if maximum violates a zoom level dependent threshold
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if (max_distance > detail::DOUGLAS_PEUCKER_THRESHOLDS[zoom_level])
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{
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// mark idx as necessary
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is_necessary[farthest_entry_index] = true;
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if (pair.first < farthest_entry_index)
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{
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recursion_stack.emplace(pair.first, farthest_entry_index);
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}
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if (farthest_entry_index < pair.second)
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{
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recursion_stack.emplace(farthest_entry_index, pair.second);
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}
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}
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}
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auto simplified_size = std::count(is_necessary.begin(), is_necessary.end(), true);
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std::vector<util::Coordinate> simplified_geometry;
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simplified_geometry.reserve(simplified_size);
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for (auto idx : util::irange<std::size_t>(0UL, size))
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{
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if (is_necessary[idx])
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{
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simplified_geometry.push_back(begin[idx]);
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}
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}
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return simplified_geometry;
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}
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} // namespace osrm::engine
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