Use DouglasPeucker with squaredEuclideanDistance
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Patrick Niklaus
parent
67834def5f
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4886d46d91
@ -12,26 +12,47 @@ namespace engine
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{
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namespace detail
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{
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const constexpr int DOUGLAS_PEUCKER_THRESHOLDS[19] = {
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512440, // z0
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256720, // z1
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122560, // z2
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56780, // z3
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28800, // z4
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14400, // z5
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7200, // z6
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3200, // z7
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2400, // z8
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1000, // z9
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600, // z10
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120, // z11
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60, // z12
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45, // z13
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36, // z14
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20, // z15
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8, // z16
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6, // z17
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4, // z18
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// This is derived from the following formular:
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// x = b * (1 + lon/180) => dx = b * dlon/180
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// y = b * (1 - lat/180) => dy = b * dlat/180
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// dx^2 + dy^2 < min_pixel^2
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// => dlon^2 + dlat^2 < min_pixel^2 / b^2 * 180^2
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inline std::vector<std::uint64_t> generateThreshold(double min_pixel, unsigned number_of_zoomlevels)
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{
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std::vector<std::uint64_t> thresholds(number_of_zoomlevels);
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for (unsigned zoom = 0; zoom < number_of_zoomlevels; ++zoom)
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{
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const double shift = (1u << zoom) * 256;
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const double b = shift / 2.0;
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const double pixel_to_deg = 180. / b;
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const std::uint64_t min_deg = min_pixel * pixel_to_deg * COORDINATE_PRECISION;
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thresholds[zoom] = min_deg * min_deg;
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}
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return thresholds;
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}
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const constexpr std::uint64_t DOUGLAS_PEUCKER_THRESHOLDS[19] = {
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49438476562500, // z0
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12359619140625, // z1
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3089903027344, // z2
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772475756836, // z3
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193118939209, // z4
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48279515076, // z5
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12069878769, // z6
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3017414761, // z7
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754326225, // z8
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188567824, // z9
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47141956, // z10
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11785489, // z11
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2944656, // z12
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736164, // z13
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184041, // z14
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45796, // z15
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11449, // z16
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2809, // z17
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676, // z18
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};
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const constexpr auto DOUGLAS_PEUCKER_THRESHOLDS_SIZE =
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@ -16,6 +16,31 @@ namespace osrm
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namespace engine
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{
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struct FastPerpendicularDistance
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{
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FastPerpendicularDistance(const util::Coordinate start, const util::Coordinate target)
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: projected_start(util::coordinate_calculation::mercator::fromWGS84(start)),
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projected_target(util::coordinate_calculation::mercator::fromWGS84(target))
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{
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}
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// Normed to the thresholds table
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std::uint64_t operator()(const util::Coordinate coordinate) const
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{
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auto projected = util::coordinate_calculation::mercator::fromWGS84(coordinate);
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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(projected_start, projected_target,
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projected);
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auto squared_distance = util::coordinate_calculation::squaredEuclideanDistance(projected,
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projected_point_on_segment);
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return squared_distance;
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}
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const util::FloatCoordinate projected_start;
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const util::FloatCoordinate projected_target;
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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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@ -51,14 +76,16 @@ std::vector<util::Coordinate> douglasPeucker(std::vector<util::Coordinate>::cons
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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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double max_distance = 0;
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std::uint64_t max_distance = 0;
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auto farthest_entry_index = pair.second;
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FastPerpendicularDistance perpendicular_distance(begin[pair.first], begin[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 = perpendicularDistance(begin[pair.first], begin[pair.second], begin[idx]);
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const auto distance = perpendicular_distance(begin[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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@ -1,4 +1,5 @@
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#include "engine/douglas_peucker.hpp"
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#include "util/coordinate_calculation.hpp"
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#include <boost/test/unit_test.hpp>
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#include <boost/test/test_case_template.hpp>
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@ -12,6 +13,16 @@ BOOST_AUTO_TEST_SUITE(douglas_peucker_simplification)
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using namespace osrm;
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using namespace osrm::engine;
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BOOST_AUTO_TEST_CASE(calibrate_thresholds)
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{
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auto thresholds = detail::generateThreshold(5, 19);
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auto z = 0;
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for (auto t : thresholds)
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{
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BOOST_TEST_MESSAGE(t << ", // z" << z++);
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}
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}
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BOOST_AUTO_TEST_CASE(removed_middle_test)
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{
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/*
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@ -23,9 +34,9 @@ BOOST_AUTO_TEST_CASE(removed_middle_test)
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*/
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std::vector<util::Coordinate> coordinates = {
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util::Coordinate(util::FloatLongitude(5), util::FloatLatitude(5)),
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util::Coordinate(util::FloatLongitude(5.995715), util::FloatLatitude(6)),
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util::Coordinate(util::FloatLongitude(10), util::FloatLatitude(10)),
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util::Coordinate(util::FloatLongitude(15), util::FloatLatitude(5))};
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util::Coordinate(util::FloatLongitude(12.5), util::FloatLatitude(12.6096298302)),
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util::Coordinate(util::FloatLongitude(20), util::FloatLatitude(20)),
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util::Coordinate(util::FloatLongitude(25), util::FloatLatitude(5))};
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for (unsigned z = 0; z < detail::DOUGLAS_PEUCKER_THRESHOLDS_SIZE; z++)
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{
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@ -49,19 +60,19 @@ BOOST_AUTO_TEST_CASE(removed_middle_test_zoom_sensitive)
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std::vector<util::Coordinate> coordinates = {
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util::Coordinate(util::FloatLongitude(5), util::FloatLatitude(5)),
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util::Coordinate(util::FloatLongitude(6), util::FloatLatitude(6)),
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util::Coordinate(util::FloatLongitude(10), util::FloatLatitude(10)),
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util::Coordinate(util::FloatLongitude(15), util::FloatLatitude(5))};
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util::Coordinate(util::FloatLongitude(20), util::FloatLatitude(20)),
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util::Coordinate(util::FloatLongitude(25), util::FloatLatitude(5))};
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// Coordinate 6,6 should start getting included at Z12 and higher
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// Coordinate 6,6 should start getting included at Z9 and higher
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// Note that 5,5->6,6->10,10 is *not* a straight line on the surface
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// of the earth
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for (unsigned z = 0; z < 11; z++)
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for (unsigned z = 0; z < 9; z++)
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{
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auto result = douglasPeucker(coordinates, z);
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BOOST_CHECK_EQUAL(result.size(), 3);
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}
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// From 12 to max zoom, we should get all coordinates
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for (unsigned z = 12; z < detail::DOUGLAS_PEUCKER_THRESHOLDS_SIZE; z++)
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// From 9 to max zoom, we should get all coordinates
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for (unsigned z = 9; z < detail::DOUGLAS_PEUCKER_THRESHOLDS_SIZE; z++)
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{
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auto result = douglasPeucker(coordinates, z);
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BOOST_CHECK_EQUAL(result.size(), 4);
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@ -71,38 +82,39 @@ BOOST_AUTO_TEST_CASE(removed_middle_test_zoom_sensitive)
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BOOST_AUTO_TEST_CASE(remove_second_node_test)
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{
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for (unsigned z = 0; z < detail::DOUGLAS_PEUCKER_THRESHOLDS_SIZE; z++)
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// derived from the degreeToPixel function
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const auto delta_pixel_to_delta_degree = [](const int pixel, const unsigned zoom) {
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const double shift = (1u << zoom) * 256;
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const double b = shift / 2.0;
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return pixel * 180. / b;
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};
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// For zoom level 0 all gets reduced to a line
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for (unsigned z = 1; z < detail::DOUGLAS_PEUCKER_THRESHOLDS_SIZE; z++)
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{
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/*
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x--x
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| \
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x-x x
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x
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x
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x-x x
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x
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*/
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std::vector<util::Coordinate> input = {
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util::Coordinate(util::FixedLongitude(5 * COORDINATE_PRECISION),
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util::FixedLatitude(5 * COORDINATE_PRECISION)),
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util::Coordinate(util::FixedLongitude(5 * COORDINATE_PRECISION),
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util::FixedLatitude(5 * COORDINATE_PRECISION +
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detail::DOUGLAS_PEUCKER_THRESHOLDS[z])),
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util::Coordinate(util::FixedLongitude(10 * COORDINATE_PRECISION),
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util::FixedLatitude(10 * COORDINATE_PRECISION)),
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util::Coordinate(util::FixedLongitude(10 * COORDINATE_PRECISION),
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util::FixedLatitude(10 + COORDINATE_PRECISION +
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detail::DOUGLAS_PEUCKER_THRESHOLDS[z] * 2)),
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util::Coordinate(util::FixedLongitude(5 * COORDINATE_PRECISION),
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util::FixedLatitude(15 * COORDINATE_PRECISION)),
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util::Coordinate(util::FixedLongitude(5 * COORDINATE_PRECISION +
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detail::DOUGLAS_PEUCKER_THRESHOLDS[z]),
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util::FixedLatitude(15 * COORDINATE_PRECISION))};
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BOOST_TEST_MESSAGE("Threshold (" << z << "): " << detail::DOUGLAS_PEUCKER_THRESHOLDS[z]);
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util::Coordinate(util::FloatLongitude(5),
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util::FloatLatitude(5)),
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util::Coordinate(util::FloatLongitude(5 + delta_pixel_to_delta_degree(2, z)),
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util::FloatLatitude(5)),
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util::Coordinate(util::FloatLongitude(10),
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util::FloatLatitude(10)),
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util::Coordinate(util::FloatLongitude(5),
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util::FloatLatitude(15)),
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util::Coordinate(util::FloatLongitude(5),
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util::FloatLatitude(15 + delta_pixel_to_delta_degree(2, z)))};
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BOOST_TEST_MESSAGE("Delta (" << z << "): " << delta_pixel_to_delta_degree(2, z));
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auto result = douglasPeucker(input, z);
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BOOST_CHECK_EQUAL(result.size(), 4);
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BOOST_CHECK_EQUAL(result.size(), 3);
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BOOST_CHECK_EQUAL(input[0], result[0]);
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BOOST_CHECK_EQUAL(input[2], result[1]);
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BOOST_CHECK_EQUAL(input[3], result[2]);
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BOOST_CHECK_EQUAL(input[5], result[3]);
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BOOST_CHECK_EQUAL(input[4], result[2]);
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}
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}
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