根据wiki algorithm https://en.wikipedia.org/wiki/Geohash
思路:纯算法实现；32位字符： 0~9 , a~z; 字符去掉了 a,i, l, o;
// since pricision biggest is 12, each char using 5 digit which is total 60;
// divided by two (lat, lng), then each lat and lng contribute 30;
public class GeoHash {
/*
* @param latitude: one of a location coordinate pair
* @param longitude: one of a location coordinate pair
* @param precision: an integer between 1 to 12
* @return: a base32 string
*/
public String encode(double latitude, double longitude, int precision) {
String SPACE = "0123456789bcdefghjkmnpqrstuvwxyz";
String latBin = getBin(latitude, -90, 90);
String lngBin = getBin(longitude, -180, 180);
StringBuilder sb = new StringBuilder();
for(int i = 0; i < 30; i++) {
sb.append(lngBin.charAt(i));
sb.append(latBin.charAt(i));
}
StringBuilder resBuilder = new StringBuilder();
for(int i = 0; i < 60; i += 5) {
int index = getIndex(sb.substring(i, i+5));
resBuilder.append(SPACE.charAt(index));
}
return resBuilder.toString().substring(0, precision);
}
private int getIndex(String str) {
return Integer.parseInt(str, 2);
}
private String getBin(double value, double start, double end) {
// since pricision biggest is 12, each char using 5 digit which is total 60;
// divided by two (lat, lng), then each lat and lng contribute 30;
StringBuilder sb = new StringBuilder();
for(int i = 0; i < 30; i++) {
double mid = (start + end ) / 2;
if(value > mid) {
start = mid;
sb.append("1");
} else {
end = mid;
sb.append("0");
}
}
return sb.toString();
}
}