/**
* Copyright (c) 2002-2010 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.graphalgo.impl.util;
import org.neo4j.graphalgo.EstimateEvaluator;
import org.neo4j.graphdb.Node;
public class GeoEstimateEvaluator implements EstimateEvaluator<Double>
{
private static final double EARTH_RADIUS = 6371*1000; // Meters
private Node cachedGoal;
private double[] cachedGoalCoordinates;
private final String latitudePropertyKey;
private final String longitudePropertyKey;
public GeoEstimateEvaluator( String latitudePropertyKey, String longitudePropertyKey )
{
this.latitudePropertyKey = latitudePropertyKey;
this.longitudePropertyKey = longitudePropertyKey;
}
public Double getCost( Node node, Node goal )
{
double[] nodeCoordinates = getCoordinates( node );
if ( cachedGoal == null || !cachedGoal.equals( goal ) )
{
cachedGoalCoordinates = getCoordinates( goal );
cachedGoal = goal;
}
return distance( nodeCoordinates[0], nodeCoordinates[1],
cachedGoalCoordinates[0], cachedGoalCoordinates[1] );
}
private double[] getCoordinates( Node node )
{
return new double[] {
((Number) node.getProperty( latitudePropertyKey )).doubleValue(),
((Number) node.getProperty( longitudePropertyKey )).doubleValue()
};
}
private double distance( double latitude1, double longitude1,
double latitude2, double longitude2 )
{
latitude1 = Math.toRadians( latitude1 );
longitude1 = Math.toRadians( longitude1 );
latitude2 = Math.toRadians( latitude2 );
longitude2 = Math.toRadians( longitude2 );
double cLa1 = Math.cos( latitude1 );
double x_A = EARTH_RADIUS * cLa1 * Math.cos( longitude1 );
double y_A = EARTH_RADIUS * cLa1 * Math.sin( longitude1 );
double z_A = EARTH_RADIUS * Math.sin( latitude1 );
double cLa2 = Math.cos( latitude2 );
double x_B = EARTH_RADIUS * cLa2 * Math.cos( longitude2 );
double y_B = EARTH_RADIUS * cLa2 * Math.sin( longitude2 );
double z_B = EARTH_RADIUS * Math.sin( latitude2 );
return Math.sqrt( ( x_A - x_B ) * ( x_A - x_B ) + ( y_A - y_B )
* ( y_A - y_B ) + ( z_A - z_B ) * ( z_A - z_B ) );
}
}