Lucene example source code file (GeoHashUtils.java)

This example Lucene source code file (GeoHashUtils.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

base_32, bits, bits, decode_map, geohashutils, geohashutils, hashmap, map, precision, precision, string, stringbuilder, stringbuilder, util

The Lucene GeoHashUtils.java source code

/**
 * 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
 * <a href="http://en.wikipedia.org/wiki/Geohash">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();

  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};
	}
}