java 版本的 geohash 算法解析
package com.sun.tools;
import java.text.DecimalFormat;
import java.util.BitSet;
import java.util.HashMap;
public class Geohash {
private static int numbits = 6 * 5;
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' };
final static HashMap<Character, Integer> lookup = new HashMap<Character, Integer>();
static {
int i = 0;
for (char c : digits) {
lookup.put(c, i++);
}
}
public static void main(String[] args) {
double[] latlon = new Geohash().decode("dj248j248j24");
System.out.println(latlon[0] + " " + latlon[1]);
Geohash e = new Geohash();
String s = e.encode(30, -90.0);
System.out.println(s);
latlon = e.decode(s);
DecimalFormat df = new DecimalFormat("0.00000");
System.out.println(df.format(latlon[0]) + ", " + df.format(latlon[1]));
}
/**
* 将Geohash字串解码成经纬值
*
* @param geohash
* 待解码的Geohash字串
* @return 经纬值数组
*/
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();
// even bits
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);
}
// odd bits
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 lat = decode(latset, -90, 90);
double lon = decode(lonset, -180, 180);
DecimalFormat df = new DecimalFormat("0.00000");
return new double[] { Double.parseDouble(df.format(lat)), Double.parseDouble(df.format(lon)) };
}
/**
* 根据二进制编码串和指定的数值变化范围，计算得到经/纬值
*
* @param bs
* 经/纬二进制编码串
* @param floor
* 下限
* @param ceiling
* 上限
* @return 经/纬值
*/
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;
}
/**
* 根据经纬值得到Geohash字串
*
* @param lat
* 纬度值
* @param lon
* 经度值
* @return Geohash字串
*/
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');
}
return base32(Long.parseLong(buffer.toString(), 2));
}
/**
* 将二进制编码串转换成Geohash字串
*
* @param i
* 二进制编码串
* @return Geohash字串
*/
public static 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));
}
/**
* 得到经/纬度对应的二进制编码
*
* @param lat
* 经/纬度
* @param floor
* 下限
* @param ceiling
* 上限
* @return 二进制编码串
*/
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;
}
}
