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Optimise encodePolyline function (#6940)

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Siarhei Fedartsou 2024-06-22 20:04:32 +02:00 committed by GitHub
parent 3d01d96036
commit 7d72dfebf7
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4 changed files with 122 additions and 47 deletions
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1
CHANGELOG.md
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@ -24,6 +24,7 @@
- NodeJS:
- CHANGED: Use node-api instead of NAN. [#6452](https://github.com/Project-OSRM/osrm-backend/pull/6452)
- Misc:
- CHANGED: Optimise encodePolyline function. [#6940](https://github.com/Project-OSRM/osrm-backend/pull/6940)
- CHANGED: Avoid reallocations in base64 encoding. [#6951](https://github.com/Project-OSRM/osrm-backend/pull/6951)
- CHANGED: Get rid of unused Boost dependencies. [#6960](https://github.com/Project-OSRM/osrm-backend/pull/6960)
- CHANGED: Apply micro-optimisation for Table & Trip APIs. [#6949](https://github.com/Project-OSRM/osrm-backend/pull/6949)

37
include/engine/polyline_compressor.hpp
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@ -12,7 +12,7 @@ namespace osrm::engine
{
namespace detail
{
std::string encode(std::vector<int> &numbers);
void encode(int number_to_encode, std::string &output);
std::int32_t decode_polyline_integer(std::string::const_iterator &first,
std::string::const_iterator last);
} // namespace detail
@ -30,27 +30,24 @@ std::string encodePolyline(CoordVectorForwardIter begin, CoordVectorForwardIter
return {};
}
std::vector<int> delta_numbers;
BOOST_ASSERT(size > 0);
delta_numbers.reserve((size - 1) * 2);
std::string output;
// just a guess that we will need ~4 bytes per coordinate to avoid reallocations
output.reserve(size * 4);
int current_lat = 0;
int current_lon = 0;
std::for_each(
begin,
end,
[&delta_numbers, &current_lat, &current_lon, coordinate_to_polyline](
const util::Coordinate loc)
{
const int lat_diff =
std::round(static_cast<int>(loc.lat) * coordinate_to_polyline) - current_lat;
const int lon_diff =
std::round(static_cast<int>(loc.lon) * coordinate_to_polyline) - current_lon;
delta_numbers.emplace_back(lat_diff);
delta_numbers.emplace_back(lon_diff);
current_lat += lat_diff;
current_lon += lon_diff;
});
return detail::encode(delta_numbers);
for (auto it = begin; it != end; ++it)
{
const int lat_diff =
std::round(static_cast<int>(it->lat) * coordinate_to_polyline) - current_lat;
const int lon_diff =
std::round(static_cast<int>(it->lon) * coordinate_to_polyline) - current_lon;
detail::encode(lat_diff, output);
detail::encode(lon_diff, output);
current_lat += lat_diff;
current_lon += lon_diff;
}
return output;
}
// Decodes geometry from polyline format

39
src/engine/polyline_compressor.cpp
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@ -10,9 +10,19 @@
namespace osrm::engine::detail // anonymous to keep TU local
{
std::string encode(int number_to_encode)
void encode(int number_to_encode, std::string &output)
{
std::string output;
if (number_to_encode < 0)
{
const unsigned binary = std::llabs(number_to_encode);
const unsigned twos = (~binary) + 1u;
const unsigned shl = twos << 1u;
number_to_encode = static_cast<int>(~shl);
}
else
{
number_to_encode <<= 1u;
}
while (number_to_encode >= 0x20)
{
const int next_value = (0x20 | (number_to_encode & 0x1f)) + 63;
@ -22,31 +32,6 @@ std::string encode(int number_to_encode)
number_to_encode += 63;
output += static_cast<char>(number_to_encode);
return output;
}
std::string encode(std::vector<int> &numbers)
{
std::string output;
for (auto &number : numbers)
{
if (number < 0)
{
const unsigned binary = std::llabs(number);
const unsigned twos = (~binary) + 1u;
const unsigned shl = twos << 1u;
number = static_cast<int>(~shl);
}
else
{
number <<= 1u;
}
}
for (const int number : numbers)
{
output += encode(number);
}
return output;
}
// https://developers.google.com/maps/documentation/utilities/polylinealgorithm

92
unit_tests/engine/polyline_compressor.cpp
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@ -45,4 +45,96 @@ BOOST_AUTO_TEST_CASE(polyline6_test_case)
decodePolyline<1000000>(encodePolyline<1000000>(coords.begin(), coords.end())).begin()));
}
BOOST_AUTO_TEST_CASE(empty_polyline_test)
{
using namespace osrm::engine;
using namespace osrm::util;
std::vector<Coordinate> empty_coords;
BOOST_CHECK_EQUAL(encodePolyline(empty_coords.begin(), empty_coords.end()), "");
BOOST_CHECK(decodePolyline("").empty());
}
BOOST_AUTO_TEST_CASE(polyline_single_point_test)
{
using namespace osrm::engine;
using namespace osrm::util;
const std::vector<Coordinate> coords({{FixedLongitude{-122414000}, FixedLatitude{37776000}}});
const std::string encoded = encodePolyline(coords.begin(), coords.end());
BOOST_CHECK_EQUAL(encoded, "_cqeFn~cjV");
const auto decoded = decodePolyline(encoded);
BOOST_CHECK_EQUAL(decoded.size(), 1);
BOOST_CHECK_EQUAL(decoded[0].lon, FixedLongitude{-122414000});
BOOST_CHECK_EQUAL(decoded[0].lat, FixedLatitude{37776000});
}
BOOST_AUTO_TEST_CASE(polyline_multiple_points_test)
{
using namespace osrm::engine;
using namespace osrm::util;
const std::vector<Coordinate> coords({{FixedLongitude{-122414000}, FixedLatitude{37776000}},
{FixedLongitude{-122420000}, FixedLatitude{37779000}},
{FixedLongitude{-122421000}, FixedLatitude{37780000}}});
const std::string encoded = encodePolyline(coords.begin(), coords.end());
BOOST_CHECK_EQUAL(encoded, "_cqeFn~cjVwQnd@gEfE");
const auto decoded = decodePolyline(encoded);
BOOST_CHECK_EQUAL(decoded.size(), 3);
for (size_t i = 0; i < coords.size(); ++i)
{
BOOST_CHECK_EQUAL(decoded[i].lon, coords[i].lon);
BOOST_CHECK_EQUAL(decoded[i].lat, coords[i].lat);
}
}
BOOST_AUTO_TEST_CASE(polyline_large_coordinate_difference_test)
{
using namespace osrm::engine;
using namespace osrm::util;
const std::vector<Coordinate> coords({{FixedLongitude{-179000000}, FixedLatitude{-89000000}},
{FixedLongitude{179000000}, FixedLatitude{89000000}}});
const std::string encoded = encodePolyline(coords.begin(), coords.end());
BOOST_CHECK_EQUAL(encoded, "~xe~O~|oca@_sl}`@_{`hcA");
const auto decoded = decodePolyline(encoded);
BOOST_CHECK_EQUAL(decoded.size(), 2);
for (size_t i = 0; i < coords.size(); ++i)
{
BOOST_CHECK_EQUAL(decoded[i].lon, coords[i].lon);
BOOST_CHECK_EQUAL(decoded[i].lat, coords[i].lat);
}
}
BOOST_AUTO_TEST_CASE(roundtrip)
{
using namespace osrm::engine;
using namespace osrm::util;
{
const auto encoded = "_chxEn`zvN\\\\]]";
const auto decoded = decodePolyline(encoded);
const auto reencoded = encodePolyline(decoded.begin(), decoded.end());
BOOST_CHECK_EQUAL(encoded, reencoded);
}
{
const auto encoded =
"gcneIpgxzRcDnBoBlEHzKjBbHlG`@`IkDxIiKhKoMaLwTwHeIqHuAyGXeB~Ew@fFjAtIzExF";
const auto decoded = decodePolyline(encoded);
const auto reencoded = encodePolyline(decoded.begin(), decoded.end());
BOOST_CHECK_EQUAL(encoded, reencoded);
}
{
const auto encoded = "_p~iF~ps|U_ulLnnqC_mqNvxq`@";
const auto decoded = decodePolyline(encoded);
const auto reencoded = encodePolyline(decoded.begin(), decoded.end());
BOOST_CHECK_EQUAL(encoded, reencoded);
}
}
BOOST_AUTO_TEST_SUITE_END()