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GraphHopper is a fast and memory efficient Java road routing engine working seamlessly with OpenStreetMap data.
There is a newer version: 10.0
/*
 *  Licensed to GraphHopper GmbH under one or more contributor
 *  license agreements. See the NOTICE file distributed with this work for
 *  additional information regarding copyright ownership.
 *
 *  GraphHopper GmbH 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;

public class Instructions {

    /**
     * This method is useful for navigation devices to find the next instruction for the specified
     * coordinate (e.g. the current position).
     * 
     *
     * @param instructions the instructions to query
     * @param maxDistance the maximum acceptable distance to the instruction (in meter)
     * @return the next Instruction or null if too far away.
     */
    public static Instruction find(InstructionList instructions, double lat, double lon, double maxDistance) {
        // handle special cases
        if (instructions.size() == 0) {
            return null;
        }
        PointList points = instructions.get(0).getPoints();
        double prevLat = points.getLat(0);
        double prevLon = points.getLon(0);
        DistanceCalc distCalc = DistanceCalcEarth.DIST_EARTH;
        double foundMinDistance = distCalc.calcNormalizedDist(lat, lon, prevLat, prevLon);
        int foundInstruction = 0;

        // Search the closest edge to the query point
        if (instructions.size() > 1) {
            for (int instructionIndex = 0; instructionIndex < instructions.size(); instructionIndex++) {
                points = instructions.get(instructionIndex).getPoints();
                for (int pointIndex = 0; pointIndex < points.size(); pointIndex++) {
                    double currLat = points.getLat(pointIndex);
                    double currLon = points.getLon(pointIndex);

                    if (!(instructionIndex == 0 && pointIndex == 0)) {
                        // calculate the distance from the point to the edge
                        double distance;
                        int index = instructionIndex;
                        if (distCalc.validEdgeDistance(lat, lon, currLat, currLon, prevLat, prevLon)) {
                            distance = distCalc.calcNormalizedEdgeDistance(lat, lon, currLat, currLon, prevLat, prevLon);
                            if (pointIndex > 0)
                                index++;
                        } else {
                            distance = distCalc.calcNormalizedDist(lat, lon, currLat, currLon);
                            if (pointIndex > 0)
                                index++;
                        }

                        if (distance < foundMinDistance) {
                            foundMinDistance = distance;
                            foundInstruction = index;
                        }
                    }
                    prevLat = currLat;
                    prevLon = currLon;
                }
            }
        }

        if (distCalc.calcDenormalizedDist(foundMinDistance) > maxDistance)
            return null;

        // special case finish condition
        if (foundInstruction == instructions.size())
            foundInstruction--;

        return instructions.get(foundInstruction);
    }
}