geohash的编码与解码

geohash的作用：1.提高位置检索的效率；2.缩小数据包的大小

一、在项目中引入geohash

vue项目： npm i geohash -D

 

js项目：下载geohash.js代码，并放入项目中

 

二、使用encodeGeoHash和decodeGeoHash方法进行编码与解码


geohash.js文件：

 

  1 // geohash.js
  2 // Geohash library for Javascript
  3 // (c) 2008 David Troy
  4 // (c) 2010 Chris Williams
  5 // Distributed under the MIT License
  6 
  7 
  8 var GeoHash = (function () {
  9   BITS = [16, 8, 4, 2, 1];
 10 
 11   BASE32 =                         "0123456789bcdefghjkmnpqrstuvwxyz";
 12   NEIGHBORS = { right  : { even :  "bc01fg45238967deuvhjyznpkmstqrwx" },
 13                 left   : { even :  "238967debc01fg45kmstqrwxuvhjyznp" },
 14                 top    : { even :  "p0r21436x8zb9dcf5h7kjnmqesgutwvy" },
 15                 bottom : { even :  "14365h7k9dcfesgujnmqp0r2twvyx8zb" } };
 16   BORDERS   = { right  : { even : "bcfguvyz" },
 17                 left   : { even : "0145hjnp" },
 18                 top    : { even : "prxz" },
 19                 bottom : { even : "028b" } };
 20 
 21   NEIGHBORS.bottom.odd = NEIGHBORS.left.even;
 22   NEIGHBORS.top.odd = NEIGHBORS.right.even;
 23   NEIGHBORS.left.odd = NEIGHBORS.bottom.even;
 24   NEIGHBORS.right.odd = NEIGHBORS.top.even;
 25 
 26   BORDERS.bottom.odd = BORDERS.left.even;
 27   BORDERS.top.odd = BORDERS.right.even;
 28   BORDERS.left.odd = BORDERS.bottom.even;
 29   BORDERS.right.odd = BORDERS.top.even;
 30 
 31   var refine_interval = function (interval, cd, mask) {
 32     if (cd&mask)
 33       interval[0] = (interval[0] + interval[1])/2;
 34     else
 35       interval[1] = (interval[0] + interval[1])/2;
 36   };
 37 
 38   
 39 
 40 
 41 
 42   return {
 43     encodeGeoHash: function (latitude, longitude) {
 44       var is_even=1;
 45       var i=0;
 46       var lat = []; var lon = [];
 47       var bit=0;
 48       var ch=0;
 49       var precision = 12;
 50       geohash = "";
 51 
 52       lat[0] = -90.0;  lat[1] = 90.0;
 53       lon[0] = -180.0; lon[1] = 180.0;
 54 
 55       while (geohash.length < precision) {
 56         if (is_even) {
 57           mid = (lon[0] + lon[1]) / 2;
 58           if (longitude > mid) {
 59             ch |= BITS[bit];
 60             lon[0] = mid;
 61           } else
 62             lon[1] = mid;
 63         } else {
 64           mid = (lat[0] + lat[1]) / 2;
 65           if (latitude > mid) {
 66             ch |= BITS[bit];
 67             lat[0] = mid;
 68           } else
 69             lat[1] = mid;
 70         }
 71 
 72         is_even = !is_even;
 73         if (bit < 4)
 74           bit++;
 75         else {
 76           geohash += BASE32[ch];
 77           bit = 0;
 78           ch = 0;
 79         }
 80       }
 81       return geohash;
 82     },
 83     decodeGeoHash: function (geohash) {
 84       var is_even = 1;
 85       var lat = []; var lon = [];
 86       lat[0] = -90.0;  lat[1] = 90.0;
 87       lon[0] = -180.0; lon[1] = 180.0;
 88       lat_err = 90.0;  lon_err = 180.0;
 89 
 90       for (i=0; i<geohash.length; i++) {
 91         c = geohash[i];
 92         cd = BASE32.indexOf(c);
 93         for (j=0; j<5; j++) {
 94           mask = BITS[j];
 95           if (is_even) {
 96             lon_err /= 2;
 97             refine_interval(lon, cd, mask);
 98           } else {
 99             lat_err /= 2;
100             refine_interval(lat, cd, mask);
101           }
102           is_even = !is_even;
103         }
104       }
105       lat[2] = (lat[0] + lat[1])/2;
106       lon[2] = (lon[0] + lon[1])/2;
107 
108       return { latitude: lat[2], longitude: lon[2]};
109     },
110     calculateAdjacent: function (srcHash, dir) {
111       srcHash = srcHash.toLowerCase();
112       var lastChr = srcHash.charAt(srcHash.length-1);
113       var type = (srcHash.length % 2) ? 'odd' : 'even';
114       var base = srcHash.substring(0,srcHash.length-1);
115       if (BORDERS[dir][type].indexOf(lastChr)!=-1)
116         base = calculateAdjacent(base, dir);
117       return base + BASE32[NEIGHBORS[dir][type].indexOf(lastChr)];
118     }
119   };
120 })();
121 
122 if (typeof exports == "undefined") { exports = {}; }
123 
124 exports.GeoHash = GeoHash;

 

 

posted @ 2020-06-04 14:21  跳跃的皮皮虾  阅读(1933)  评论(0)  编辑  收藏  举报