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x2 speedup in Douglas Peucker by projecting all coordinates first

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This commit is contained in:
Patrick Niklaus 2016-04-30 02:11:36 +02:00
parent 378d9f4112
commit 212ad94c90
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GPG Key ID: E426891B5F978B1B
1 changed files with 22 additions and 26 deletions
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34
src/engine/douglas_peucker.cpp
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@ -17,31 +17,20 @@ namespace osrm
namespace engine namespace engine
{ {
struct FastPerpendicularDistance
{
FastPerpendicularDistance(const util::Coordinate start, const util::Coordinate target)
: projected_start(util::web_mercator::fromWGS84(start)),
projected_target(util::web_mercator::fromWGS84(target))
{
}
// Normed to the thresholds table // Normed to the thresholds table
std::uint64_t operator()(const util::Coordinate coordinate) const std::uint64_t fastPerpendicularDistance(const util::FloatCoordinate &projected_start,
const util::FloatCoordinate &projected_target,
const util::FloatCoordinate &projected)
{ {
auto projected = util::web_mercator::fromWGS84(coordinate);
util::FloatCoordinate projected_point_on_segment; util::FloatCoordinate projected_point_on_segment;
std::tie(std::ignore, projected_point_on_segment) = std::tie(std::ignore, projected_point_on_segment) =
util::coordinate_calculation::projectPointOnSegment(projected_start, projected_target, util::coordinate_calculation::projectPointOnSegment(projected_start, projected_target,
projected); projected);
auto squared_distance = util::coordinate_calculation::squaredEuclideanDistance(projected, auto squared_distance = util::coordinate_calculation::squaredEuclideanDistance(
projected_point_on_segment); projected, projected_point_on_segment);
return squared_distance; return squared_distance;
} }
const util::FloatCoordinate projected_start;
const util::FloatCoordinate projected_target;
};
std::vector<util::Coordinate> douglasPeucker(std::vector<util::Coordinate>::const_iterator begin, std::vector<util::Coordinate> douglasPeucker(std::vector<util::Coordinate>::const_iterator begin,
std::vector<util::Coordinate>::const_iterator end, std::vector<util::Coordinate>::const_iterator end,
const unsigned zoom_level) const unsigned zoom_level)
@ -55,6 +44,12 @@ std::vector<util::Coordinate> douglasPeucker(std::vector<util::Coordinate>::cons
return {}; return {};
} }
std::vector<util::FloatCoordinate> projected_coordinates(size);
std::transform(begin, end, projected_coordinates.begin(), [](const util::Coordinate coord)
{
return util::web_mercator::fromWGS84(coord);
});
std::vector<bool> is_necessary(size, false); std::vector<bool> is_necessary(size, false);
BOOST_ASSERT(is_necessary.size() >= 2); BOOST_ASSERT(is_necessary.size() >= 2);
is_necessary.front() = true; is_necessary.front() = true;
@ -80,13 +75,13 @@ std::vector<util::Coordinate> douglasPeucker(std::vector<util::Coordinate>::cons
std::uint64_t max_distance = 0; std::uint64_t max_distance = 0;
auto farthest_entry_index = pair.second; auto farthest_entry_index = pair.second;
FastPerpendicularDistance perpendicular_distance(begin[pair.first], begin[pair.second]);
// sweep over range to find the maximum // sweep over range to find the maximum
for (auto idx = pair.first + 1; idx != pair.second; ++idx) for (auto idx = pair.first + 1; idx != pair.second; ++idx)
{ {
using namespace util::coordinate_calculation; using namespace util::coordinate_calculation;
const auto distance = perpendicular_distance(begin[idx]); const auto distance = fastPerpendicularDistance(projected_coordinates[pair.first],
projected_coordinates[pair.second],
projected_coordinates[idx]);
// found new feasible maximum? // found new feasible maximum?
if (distance > max_distance && if (distance > max_distance &&
distance > detail::DOUGLAS_PEUCKER_THRESHOLDS[zoom_level]) distance > detail::DOUGLAS_PEUCKER_THRESHOLDS[zoom_level])
@ -122,6 +117,7 @@ std::vector<util::Coordinate> douglasPeucker(std::vector<util::Coordinate>::cons
simplified_geometry.push_back(begin[idx]); simplified_geometry.push_back(begin[idx]);
} }
} }
return simplified_geometry; return simplified_geometry;
} }
} // ns engine } // ns engine