/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF 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 org.apache.lucene.spatial.geohash;
import java.util.HashMap;
import java.util.Map;
/**
* Utilities for encoding and decoding geohashes. Based on
* http://en.wikipedia.org/wiki/Geohash.
*/
public class GeoHashUtils {
private static final char[] BASE_32 = {'0', '1', '2', '3', '4', '5', '6',
'7', '8', '9', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'm', 'n',
'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};
private final static Map<Character,Integer> DECODE_MAP = new HashMap<Character,Integer>();
private static final int PRECISION = 12;
private static final int[] BITS = {16, 8, 4, 2, 1};
static {
for (int i = 0; i < BASE_32.length; i++) {
DECODE_MAP.put(Character.valueOf(BASE_32[i]), Integer.valueOf(i));
}
}
private GeoHashUtils() {
}
/**
* Encodes the given latitude and longitude into a geohash
*
* @param latitude Latitude to encode
* @param longitude Longitude to encode
* @return Geohash encoding of the longitude and latitude
*/
public static String encode(double latitude, double longitude) {
double[] latInterval = {-90.0, 90.0};
double[] lngInterval = {-180.0, 180.0};
final StringBuilder geohash = new StringBuilder();
boolean isEven = true;
int bit = 0;
int ch = 0;
while (geohash.length() < PRECISION) {
double mid = 0.0;
if (isEven) {
mid = (lngInterval[0] + lngInterval[1]) / 2D;
if (longitude > mid) {
ch |= BITS[bit];
lngInterval[0] = mid;
} else {
lngInterval[1] = mid;
}
} else {
mid = (latInterval[0] + latInterval[1]) / 2D;
if (latitude > mid) {
ch |= BITS[bit];
latInterval[0] = mid;
} else {
latInterval[1] = mid;
}
}
isEven = !isEven;
if (bit < 4) {
bit++;
} else {
geohash.append(BASE_32[ch]);
bit = 0;
ch = 0;
}
}
return geohash.toString();
}
/**
* Decodes the given geohash into a latitude and longitude
*
* @param geohash Geohash to deocde
* @return Array with the latitude at index 0, and longitude at index 1
*/
public static double[] decode(String geohash) {
final double[] latInterval = {-90.0, 90.0};
final double[] lngInterval = {-180.0, 180.0};
boolean isEven = true;
double latitude;
double longitude;
for (int i = 0; i < geohash.length(); i++) {
final int cd = DECODE_MAP.get(Character.valueOf(
geohash.charAt(i))).intValue();
for (int mask : BITS) {
if (isEven) {
if ((cd & mask) != 0) {
lngInterval[0] = (lngInterval[0] + lngInterval[1]) / 2D;
} else {
lngInterval[1] = (lngInterval[0] + lngInterval[1]) / 2D;
}
} else {
if ((cd & mask) != 0) {
latInterval[0] = (latInterval[0] + latInterval[1]) / 2D;
} else {
latInterval[1] = (latInterval[0] + latInterval[1]) / 2D;
}
}
isEven = !isEven;
}
}
latitude = (latInterval[0] + latInterval[1]) / 2D;
longitude = (lngInterval[0] + lngInterval[1]) / 2D;
return new double[] {latitude, longitude};
}
}