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