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Actually compute and transmit confidence in the response

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This commit is contained in:
Patrick Niklaus 2015-02-07 15:39:07 +01:00
parent fe07f9208c
commit 1b16dd126b
2 changed files with 42 additions and 3 deletions
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5
algorithms/bayes_classifier.hpp
View File

@ -60,7 +60,7 @@ struct LaplaceDistribution
}
// FIXME implement log-probability version since its faster
double probabilityDensityFunction(const double val)
double probabilityDensityFunction(const double val) const
{
const double x = std::abs(val - location);
return 1.0 / (2*scale) * std::exp(-x / scale);
@ -75,6 +75,7 @@ class BayesClassifier
{
public:
enum class ClassLabel : unsigned {NEGATIVE = 0, POSITIVE};
using ClassificationT = std::pair<ClassLabel, double>;
BayesClassifier(const PositiveDistributionT& positive_distribution,
const NegativeDistributionT& negative_distribution,
@ -89,7 +90,7 @@ public:
/*
* Returns label and the probability of the label.
*/
std::pair<ClassLabel, double> classify(const ValueT& v)
ClassificationT classify(const ValueT& v) const
{
const double positive_postpriori = positive_apriori_probability * positive_distribution.probabilityDensityFunction(v);
const double negative_postpriori = negative_apriori_probability * negative_distribution.probabilityDensityFunction(v);

40
plugins/map_matching.hpp
View File

@ -48,6 +48,9 @@ template <class DataFacadeT> class MapMatchingPlugin : public BasePlugin
std::unordered_map<std::string, unsigned> descriptor_table;
std::shared_ptr<SearchEngine<DataFacadeT>> search_engine_ptr;
using ClassifierT = BayesClassifier<LaplaceDistribution, LaplaceDistribution, double>;
using TraceClassification = ClassifierT::ClassificationT;
public:
MapMatchingPlugin(DataFacadeT *facade)
: descriptor_string("match")
@ -69,6 +72,29 @@ template <class DataFacadeT> class MapMatchingPlugin : public BasePlugin
const std::string GetDescriptor() const final { return descriptor_string; }
TraceClassification classify(double trace_length, const std::vector<PhantomNode>& matched_nodes, int removed_points) const
{
double matching_length = 0;
for (const auto current_node : osrm::irange<std::size_t>(0, matched_nodes.size()-1))
{
matching_length += coordinate_calculation::great_circle_distance(
matched_nodes[current_node].location,
matched_nodes[current_node + 1].location);
}
double distance_feature = -std::log(trace_length / matching_length);
auto label_with_confidence = classifier.classify(distance_feature);
// "second stage classifier": if we need to remove points there is something fishy
if (removed_points > 0)
{
label_with_confidence.first = ClassifierT::ClassLabel::NEGATIVE;
label_with_confidence.second = 1.0;
}
return label_with_confidence;
}
int HandleRequest(const RouteParameters &route_parameters, JSON::Object &json_result) final
{
// check number of parameters
@ -84,6 +110,7 @@ template <class DataFacadeT> class MapMatchingPlugin : public BasePlugin
double last_distance = coordinate_calculation::great_circle_distance(
input_coords[0],
input_coords[1]);
double trace_length = 0;
for (const auto current_coordinate : osrm::irange<std::size_t>(0, input_coords.size()))
{
if (0 < current_coordinate)
@ -91,6 +118,7 @@ template <class DataFacadeT> class MapMatchingPlugin : public BasePlugin
last_distance = coordinate_calculation::great_circle_distance(
input_coords[current_coordinate - 1],
input_coords[current_coordinate]);
trace_length += last_distance;
}
if (input_coords.size()-1 > current_coordinate && 0 < current_coordinate)
@ -126,6 +154,16 @@ template <class DataFacadeT> class MapMatchingPlugin : public BasePlugin
JSON::Object debug_info;
search_engine_ptr->map_matching(candidate_lists, input_coords, uturn_indicators, matched_nodes, debug_info);
TraceClassification classification = classify(trace_length, matched_nodes, input_coords.size() - matched_nodes.size());
if (classification.first == ClassifierT::ClassLabel::POSITIVE)
{
json_result.values["confidence"] = classification.second;
}
else
{
json_result.values["confidence"] = 1-classification.second;
}
InternalRouteResult raw_route;
PhantomNodes current_phantom_node_pair;
for (unsigned i = 0; i < matched_nodes.size() - 1; ++i)
@ -183,7 +221,7 @@ template <class DataFacadeT> class MapMatchingPlugin : public BasePlugin
private:
std::string descriptor_string;
DataFacadeT *facade;
BayesClassifier<LaplaceDistribution, LaplaceDistribution, double> classifier;
ClassifierT classifier;
};
#endif /* MAP_MATCHING_PLUGIN_H */