GeoHash 算法的 Java 版实现

之前曾经做过一个类 LBS 的小需求，当时是用 redis 做的，就是这篇文章，其实 GeoHash 算法，我们也可以自己实现，具体如下：

package cn.bridgeli.demo;

import java.util.ArrayList;
import java.util.BitSet;
import java.util.HashMap;

public class GeoHash {
  /**
   * 最小纬度
   */
  public static final double MINLAT = -90;
  /**
   * 最大纬度
   */
  public static final double MAXLAT = 90;
  /**
   * 最小经度
   */
  public static final double MINLNG = -180;
  /**
   * 最大经度
   */
  public static final double MAXLNG = 180;

  /**
   * 经纬度单独编码长度
   */
  private static int numbits = 5 * 5;

  /**
   * 最小纬度
   */
  private static double minLat;
  /**
   * 最小经度
   */
  private static double minLng;

  private final static char[] digits = {'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'};

  //定义编码映射关系
  final static HashMap<Character, Integer> lookup = new HashMap<Character, Integer>();

  //初始化编码映射内容
  static {
    int i = 0;
    for (char c : digits) {
      lookup.put(c, i++);
    }
  }

  public GeoHash() {
    setMinLatLng();
  }

  public String encode(double lat, double lon) {
    BitSet latbits = getBits(lat, -90, 90);
    BitSet lonbits = getBits(lon, -180, 180);
    StringBuilder buffer = new StringBuilder();
    for (int i = 0; i < numbits; i++) {
      buffer.append((lonbits.get(i)) ? '1' : '0');
      buffer.append((latbits.get(i)) ? '1' : '0');
    }
    String code = base32(Long.parseLong(buffer.toString(), 2));
    //Log.i("okunu", "encode lat = " + lat + " lng = " + lon + " code = " + code);
    return code;
  }

  public ArrayList<String> getAroundGeoHash(double lat, double lon) {
    //Log.i("okunu", "getArroundGeoHash lat = " + lat + " lng = " + lon);
    ArrayList<String> list = new ArrayList<>();
    double uplat = lat + minLat;
    double downLat = lat - minLat;

    double leftlng = lon - minLng;
    double rightLng = lon + minLng;

    String leftUp = encode(uplat, leftlng);
    list.add(leftUp);

    String leftMid = encode(lat, leftlng);
    list.add(leftMid);

    String leftDown = encode(downLat, leftlng);
    list.add(leftDown);

    String midUp = encode(uplat, lon);
    list.add(midUp);

    String midMid = encode(lat, lon);
    list.add(midMid);

    String midDown = encode(downLat, lon);
    list.add(midDown);

    String rightUp = encode(uplat, rightLng);
    list.add(rightUp);

    String rightMid = encode(lat, rightLng);
    list.add(rightMid);

    String rightDown = encode(downLat, rightLng);
    list.add(rightDown);

    //Log.i("okunu", "getArroundGeoHash list = " + list.toString());
    return list;
  }

  //根据经纬度和范围，获取对应的二进制
  private BitSet getBits(double lat, double floor, double ceiling) {
    BitSet buffer = new BitSet(numbits);
    for (int i = 0; i < numbits; i++) {
      double mid = (floor + ceiling) / 2;
      if (lat >= mid) {
        buffer.set(i);
        floor = mid;
      } else {
        ceiling = mid;
      }
    }
    return buffer;
  }

  //将经纬度合并后的二进制进行指定的32位编码
  private String base32(long i) {
    char[] buf = new char[65];
    int charPos = 64;
    boolean negative = (i < 0);
    if (!negative) {
      i = -i;
    }
    while (i <= -32) {
      buf[charPos--] = digits[(int) (-(i % 32))];
      i /= 32;
    }
    buf[charPos] = digits[(int) (-i)];
    if (negative) {
      buf[-charPos] = '-';
    }
    return new String(buf, charPos, (65 - charPos));
  }

  private static void setMinLatLng() {
    minLat = MAXLAT - MINLAT;
    for (int i = 0; i < numbits; i++) {
      minLat /= 2.0;
    }
    minLng = MAXLNG - MINLNG;
    for (int i = 0; i < numbits; i++) {
      minLng /= 2.0;
    }
  }
  //根据二进制和范围解码
  private double decode(BitSet bs, double floor, double ceiling) {
    double mid = 0;
    for (int i = 0; i < bs.length(); i++) {
      mid = (floor + ceiling) / 2;
      if (bs.get(i)) {
        floor = mid;
      } else {
        ceiling = mid;
      }
    }
    return mid;
  }

  //对编码后的字符串解码
  public double[] decode(String geohash) {
    StringBuilder buffer = new StringBuilder();
    for (char c : geohash.toCharArray()) {
      int i = lookup.get(c) + 32;
      buffer.append(Integer.toString(i, 2).substring(1));
    }

    BitSet lonset = new BitSet();
    BitSet latset = new BitSet();

    //偶数位，经度
    int j = 0;
    for (int i = 0; i < numbits * 2; i += 2) {
      boolean isSet = false;
      if (i < buffer.length()) {
        isSet = buffer.charAt(i) == '1';
      }
      lonset.set(j++, isSet);
    }

    //奇数位，纬度
    j = 0;
    for (int i = 1; i < numbits * 2; i += 2) {
      boolean isSet = false;
      if (i < buffer.length()) {
        isSet = buffer.charAt(i) == '1';
      }
      latset.set(j++, isSet);
    }

    double lon = decode(lonset, -180, 180);
    double lat = decode(latset, -90, 90);

    return new double[]{lat, lon};
  }

  public void static void main(String[] args) {
    GeoHash geohash = new GeoHash();
    String s = geohash.encode(39.923201, 116.390705);
    System.out.println("geohash：" + s);
    ArrayList<String> aroundGeoHash = geohash.getAroundGeoHash(39.923201, 116.390705);
    for (String s1 : aroundGeoHash) {
      System.out.println("aroundGeoHash：" + s1);
    }
    double[] geo = geohash.decode(s);
    System.out.println(geo[0] + " " + geo[1]);
  }
}

参考：https://www.jianshu.com/p/2fd0cf12e5ba