PolylineEncoder.java

/*  This file is part of Openrouteservice.
 *
 *  Openrouteservice is free software; you can redistribute it and/or modify it under the terms of the
 *  GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1
 *  of the License, or (at your option) any later version.

 *  This library 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 Lesser General Public License for more details.

 *  You should have received a copy of the GNU Lesser General Public License along with this library;
 *  if not, see <https://www.gnu.org/licenses/>.
 */
package org.heigit.ors.util;

import org.locationtech.jts.geom.Coordinate;

public class PolylineEncoder {
    private PolylineEncoder() {
    }

    public static String encode(final Coordinate[] coords, boolean includeElevation, StringBuilder buffer) {
        long lat;
        long lon;
        long prevLat = 0;
        long prevLon = 0;
        long elev = 0;
        long prevEle = 0;

        buffer.setLength(0);

        for (final Coordinate c : coords) {
            lat = Math.round(c.y * 1e5);
            lon = Math.round(c.x * 1e5);

            encode(lat - prevLat, buffer);
            encode(lon - prevLon, buffer);

            // Note that encoding elevation is not supported by the official polyline encoding
            if (includeElevation) {
                elev = (long) Math.floor(c.z * 100);
                encode(elev - prevEle, buffer);
                prevEle = elev;
            }

            prevLat = lat;
            prevLon = lon;
        }

        return buffer.toString();
    }

    private static void encode(long v, StringBuilder buffer) {
        v = v < 0 ? ~(v << 1) : v << 1;

        while (v >= 0x20) {
            buffer.append(Character.toChars((int) ((0x20 | (v & 0x1f)) + 63)));
            v >>= 5;
        }

        buffer.append(Character.toChars((int) (v + 63)));
    }
}