MapMatching Blog post at http://karussell.wordpress.com/2014/07/28/digitalizing-gpx-points-or-how-to-track-vehicles-with-graphhopper/

MapMatchingExample1.java

/*
 *  Licensed to Peter Karich under one or more contributor license
 *  agreements. See the NOTICE file distributed with this work for
 *  additional information regarding copyright ownership.
 *
 *  Peter Karich licenses this file to you under the Apache License,
 *  Version 2.0 (the "License"); you may not use this file except
 *  in compliance with the License. You may obtain a copy of the
 *  License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package com.graphhopper.util;

import com.graphhopper.GraphHopper;
import com.graphhopper.routing.util.EdgeFilter;
import com.graphhopper.storage.index.LocationIndex;
import com.graphhopper.storage.index.QueryResult;
import java.util.ArrayList;
import java.util.List;

/**
 * @author Peter Karich
 */
public class MapMatchingExample1
{
    public static void main( String[] args )
    {
        new MapMatchingExample1().start(args);
    }

    private void start( String[] args )
    {
        GraphHopper hopper = new GraphHopper().
                init(CmdArgs.read(args)).
                disableCHShortcuts().
                setOSMFile("your-area.pbf").
                // we look 20meter around the point, e.g. the device has such an error for GPS measurement
                setPreciseIndexResolution(20);
        hopper.importOrLoad();
                
        LocationIndex locationIndex = hopper.getLocationIndex();
        
        // User task: get the list somewhere
        List<GPXEntry> gpxList = getList();
        List<QueryResult> result = new ArrayList<QueryResult>();
        for (int i = 0; i < gpxList.size(); i++)
        {
            GPXEntry gpx = gpxList.get(i);
            QueryResult closest = locationIndex.findClosest(gpx.getLat(), gpx.getLon(), EdgeFilter.ALL_EDGES);
            if (!closest.isValid())
                throw new IllegalStateException("no close edge found for " + gpx);
            result.add(closest);
        }
        System.out.println(result);
    }

    private List<GPXEntry> getList()
    {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }
}

MapMatchingExample2.java

/*
 *  Licensed to Peter Karich under one or more contributor license
 *  agreements. See the NOTICE file distributed with this work for
 *  additional information regarding copyright ownership.
 *
 *  Peter Karich licenses this file to you under the Apache License,
 *  Version 2.0 (the "License"); you may not use this file except
 *  in compliance with the License. You may obtain a copy of the
 *  License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package com.graphhopper.util;

import com.graphhopper.GraphHopper;
import com.graphhopper.routing.DijkstraBidirectionRef;
import com.graphhopper.routing.Path;
import com.graphhopper.routing.util.EdgeFilter;
import com.graphhopper.routing.util.EncodingManager;
import com.graphhopper.routing.util.FastestWeighting;
import com.graphhopper.routing.util.FlagEncoder;
import com.graphhopper.routing.util.Weighting;
import com.graphhopper.storage.RAMDirectory;
import com.graphhopper.storage.index.LocationIndex;
import com.graphhopper.storage.index.LocationIndexTree;
import com.graphhopper.storage.index.QueryResult;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * @author Peter Karich
 */
public class MapMatchingExample2
{
    public static void main( String[] args )
    {
        new MapMatchingExample2().start(args);
    }

    private void start( String[] args )
    {
        GraphHopper hopper = new GraphHopper().
                // provide a config ...
                // init(CmdArgs.read(args)).
                // or do it programmatically:                
                disableCHShortcuts().
                setEncodingManager(new EncodingManager("CAR")).
                setGraphHopperLocation("graphhopper-out-folder/").
                setOSMFile("/media/SAMSUNG/maps/berlin.pbf");
        hopper.importOrLoad();

        LocationIndex locationIndex = createLocationIndex(hopper);

        List<GPXEntry> gpxList = getList();
        List<QueryResult> queryResults = new ArrayList<QueryResult>();
        for (int i = 0; i < gpxList.size(); i++)
        {
            GPXEntry gpx = gpxList.get(i);
            QueryResult closest = locationIndex.findClosest(gpx.getLat(), gpx.getLon(), EdgeFilter.ALL_EDGES);
            if (!closest.isValid())
                throw new IllegalStateException("no close edge found for " + gpx);
            queryResults.add(closest);
        }

        final Map<Integer, Double> edgesMap = convert(queryResults);

        final FlagEncoder flagEncoder = hopper.getEncodingManager().getSingle();
        Weighting weighting = new FastestWeighting(flagEncoder)
        {

            @Override
            public double calcWeight( EdgeIteratorState edge, boolean reverse )
            {
                Double value = edgesMap.get(edge.getEdge());
                double speed;
                if (reverse)
                    speed = flagEncoder.getReverseSpeed(edge.getFlags());
                else
                    speed = flagEncoder.getSpeed(edge.getFlags());

                if (value == null)
                    // Do not completely exclude edges which are not in our edgesMap
                    // because this could be just a signal loss or tunnel etc
                    return 10000 * edge.getDistance() / speed;

                // The larger the distance to the edge is the more penalty we put on it
                return (edge.getDistance() + value * 5) / speed;
            }
        };

        QueryResult firstQR = queryResults.get(0);
        QueryResult lastQR = queryResults.get(queryResults.size() - 1);

        DijkstraBidirectionRef dijkstra = new DijkstraBidirectionRef(hopper.getGraph(), flagEncoder, weighting);
        Path p = dijkstra.calcPath(firstQR, lastQR);         
        System.out.println(p);
        // Now loop over the edges and associate the GPX points to them with the help of our QueryResults which contains 
        // the snapped point AND the edge id.
        // p.calcEdges();
    }

    // User task: get the list e.g. from text file
    private List<GPXEntry> getList()
    {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    // User task: convert the query results in a Map which maps edgeId (obtained via queryResult.getClosestEdge().getEdge()) 
    // to distance (queryResult.getQueryDistance())
    private Map<Integer, Double> convert( List<QueryResult> queryResult )
    {
        // loop and do: map.put(qr.getClosestEdge().getEdge(), qr.getQueryDistance());
        throw new UnsupportedOperationException("Not supported yet.");
    }

    // User task: subclass LocationIndexTree and implement a method which returns the 3 best matching edges
    // instead of only one.
    private LocationIndex createLocationIndex( GraphHopper hopper )
    {
        LocationIndex locationIndex = new LocationIndexTree(hopper.getGraph(), new RAMDirectory());
        locationIndex.setResolution(20);
        locationIndex.prepareIndex();
        return locationIndex;
    }
}

MapMatchingExample3.java

/*
 *  Licensed to Peter Karich under one or more contributor license
 *  agreements. See the NOTICE file distributed with this work for
 *  additional information regarding copyright ownership.
 *
 *  Peter Karich licenses this file to you under the Apache License,
 *  Version 2.0 (the "License"); you may not use this file except
 *  in compliance with the License. You may obtain a copy of the
 *  License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package com.graphhopper.util;

import com.graphhopper.GraphHopper;
import com.graphhopper.routing.util.EdgeFilter;
import com.graphhopper.storage.index.LocationIndex;
import com.graphhopper.storage.index.QueryResult;
import java.util.ArrayList;
import java.util.List;

/**
 * @author Peter Karich
 */
public class MapMatchingExample3
{
    public static void main( String[] args )
    {
        new MapMatchingExample3().start(args);
    }

    private void start( String[] args )
    {
    
    }
}