MapUtil.java

/**
 * An utility to encode the point in GoogleMap API
 * Reference see this {@link https://developers.google.com/maps/documentation/utilities/polylinealgorithm?csw=1}
 * @author SRIN
 *
 */
public class MapUtil {

	/**
	 * Step 1 : Take the decimal value and multiply it by 1e5, rounding the
	 * result
	 * 
	 * @param value
	 *            double value of a point
	 * @return decimal value after multiply it by 1e5 and rounding the result
	 */
	private static int floor(double value) {
		return (int) java.lang.Math.round(value * 1e5);
	}

	/**
	 * Step 3 : Convert the decimal value to binary. Note that a negative value
	 * must be calculated using its two's complement by inverting the binary
	 * value and adding one to the result
	 * 
	 * Step 4 : Left-shift the binary value one bit 
	 * 
	 * Step 5 : If the original
	 * decimal value is negative, invert this encoding
	 * 
	 * @param number of the decimal value
	 * @return the encoded point
	 */
	private static String encodeSignedNumber(int num) {
		int sgn_num = num << 1;
		if (num < 0) {
			sgn_num = ~(sgn_num); // inverse the bit : ~(101) will be 010
		}
		return (encodeNumber(sgn_num));
	}

	/**
	 * Step 7 : Place the 5-bit chunks into reverse order
	 * Step 8 : OR each value with 0x20 if another bit chunk 
	 * Step 9 : Convert each value to decimal
	 * Step 10 : Add 63 to each value
	 * @param num of decimal value
	 * @return
	 */
	private static String encodeNumber(int num) {

		StringBuffer encodeString = new StringBuffer();

		while (num >= 0x20) {
			encodeString.append((char) ((0x20 | (num & 0x1f)) + 63));
			num >>= 5;
		}

		encodeString.append((char) (num + 63));

		return encodeString.toString();

	}

	/**
	 * encoded the single double value
	 * @param value single value from a point
	 * @return
	 */
	private static String encoded(double value) {
		int floor = floor(value);
		return encodeSignedNumber(floor);
	}

	/**
	 * encoded given latitude and longitude of points.
	 * 
	 * @param glatlngs
	 *            Object with latitude and long given
	 * @return encoded string for the url
	 */
	public static String encoded(GLatLong... glatlngs) {
		String enc = "";
		GLatLong prev = null;
		for (GLatLong gLatLong : glatlngs) {
			if (prev == null) {
				enc += encoded(gLatLong.getLat()) + encoded(gLatLong.getLng());
			} else {
				enc += encoded(gLatLong.getLat() - prev.getLat())
						+ encoded(gLatLong.getLng() - prev.getLng());
			}
			prev = gLatLong;
		}
		return enc;
	}

	/**
	 * Internal class to set a latitude and longitude of a point
	 * 
	 * @author SRIN
	 * 
	 */
	public static class GLatLong {

		private double lat;
		private double lng;

		public double getLat() {
			return lat;
		}

		private void setLat(double lat) {
			this.lat = lat;
		}

		public double getLng() {
			return lng;
		}

		private void setLng(double lng) {
			this.lng = lng;
		}

		public GLatLong(double lat, double lng) {
			setLat(lat);
			setLng(lng);
		}
	}
}