Open-Harbor/osrm-backend
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Make matching thresholds adaptable to different sample lengths

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This commit is contained in:
Patrick Niklaus 2015-08-26 23:27:47 +02:00
parent a4f558181d
commit a5ee82b0d1
1 changed files with 41 additions and 8 deletions
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49
routing_algorithms/map_matching.hpp
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@ -59,10 +59,9 @@ using CandidateLists = std::vector<CandidateList>;
using HMM = HiddenMarkovModel<CandidateLists>;
using SubMatchingList = std::vector<SubMatching>;
constexpr static const unsigned MAX_BROKEN_STATES = 6;
constexpr static const unsigned MAX_BROKEN_TIME = 60;
constexpr static const unsigned MAX_BROKEN_STATES = 10;
constexpr static const unsigned MAX_DISTANCE_DELTA = 200;
constexpr static const double MAX_SPEED = 180 / 3.6; // 150km -> m/s
constexpr static const unsigned SUSPICIOUS_DISTANCE_DELTA = 100;
constexpr static const double default_beta = 5.0;
@ -78,6 +77,19 @@ class MapMatching final : public BasicRoutingInterface<DataFacadeT, MapMatching<
using QueryHeap = SearchEngineData::QueryHeap;
SearchEngineData &engine_working_data;
unsigned GetAverageSampleTime(const std::vector<unsigned>& timestamps) const
{
BOOST_ASSERT(timestamps.size() > 1);
std::vector<unsigned> sample_times(timestamps.size());
std::adjacent_difference(timestamps.begin(), timestamps.end(), sample_times.begin());
// don't use first element of sample_times -> will not be a difference.
auto sum_sample_times = std::accumulate(std::next(sample_times.begin()), sample_times.end(), 0);
return sum_sample_times / (sample_times.size() - 1);
}
public:
MapMatching(DataFacadeT *facade, SearchEngineData &engine_working_data)
: super(facade), engine_working_data(engine_working_data)
@ -91,7 +103,29 @@ class MapMatching final : public BasicRoutingInterface<DataFacadeT, MapMatching<
const double gps_precision,
osrm::matching::SubMatchingList &sub_matchings) const
{
BOOST_ASSERT(!candidates_list.empty() && !trace_coordinates.empty());
BOOST_ASSERT(candidates_list.size() == trace_coordinates.size());
const auto avg_sample_time = [&]() {
if (trace_timestamps.size() > 1)
{
return GetAverageSampleTime(trace_timestamps);
}
else
{
return 0u;
}
}();
const auto max_broken_time = avg_sample_time * osrm::matching::MAX_BROKEN_STATES;
const auto max_distance_delta = [&]() {
if (trace_timestamps.size() > 1)
{
return avg_sample_time * osrm::matching::MAX_SPEED;
}
else
{
return std::numeric_limits<double>::max();
}
}();
// TODO replace default values with table lookup based on sampling frequency
EmissionLogProbability emission_log_probability(
@ -126,7 +160,7 @@ class MapMatching final : public BasicRoutingInterface<DataFacadeT, MapMatching<
trace_split =
trace_split ||
(trace_timestamps[t] - trace_timestamps[prev_unbroken_timestamps.back()] >
osrm::matching::MAX_BROKEN_TIME);
max_broken_time);
}
else
{
@ -179,8 +213,6 @@ class MapMatching final : public BasicRoutingInterface<DataFacadeT, MapMatching<
engine_working_data.InitializeOrClearFirstThreadLocalStorage(
super::facade->GetNumberOfNodes());
engine_working_data.InitializeOrClearSecondThreadLocalStorage(
super::facade->GetNumberOfNodes());
QueryHeap &forward_heap = *(engine_working_data.forward_heap_1);
QueryHeap &reverse_heap = *(engine_working_data.reverse_heap_1);
@ -196,6 +228,7 @@ class MapMatching final : public BasicRoutingInterface<DataFacadeT, MapMatching<
for (const auto s_prime : osrm::irange<std::size_t>(0u, current_viterbi.size()))
{
// how likely is candidate s_prime at time t to be emitted?
// FIXME this can be pre-computed
const double emission_pr =
emission_log_probability(candidates_list[t][s_prime].second);
double new_value = prev_viterbi[s] + emission_pr;
@ -218,7 +251,7 @@ class MapMatching final : public BasicRoutingInterface<DataFacadeT, MapMatching<
const auto d_t = std::abs(network_distance - great_circle_distance);
// very low probability transition -> prune
if (d_t > osrm::matching::MAX_DISTANCE_DELTA)
if (d_t > max_distance_delta)
{
continue;
}