/
geohash.go
88 lines (80 loc) · 1.77 KB
/
geohash.go
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// Copyright (C) 2014 Constantin Schomburg <me@cschomburg.com>
// Based on Tomi Hiltunen's work (https://github.com/TomiHiltunen/geohash-golang)
//
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
package location
import "bytes"
var (
bits = []int{16, 8, 4, 2, 1}
base32 = []byte("0123456789bcdefghjkmnpqrstuvwxyz")
)
func DecodeGeohash(geohash string) *BoundingBox {
isEven := true
lat := []float64{-90, 90}
lng := []float64{-180, 180}
latErr := float64(90)
lngErr := float64(180)
var c string
var cd int
for i := 0; i < len(geohash); i++ {
c = geohash[i : i+1]
cd = bytes.Index(base32, []byte(c))
for j := 0; j < 5; j++ {
if isEven {
lngErr /= 2
lng = refineInterval(lng, cd, bits[j])
} else {
latErr /= 2
lat = refineInterval(lat, cd, bits[j])
}
isEven = !isEven
}
}
return &BoundingBox{lat[0], lat[1], lng[0], lng[1]}
}
func EncodeGeohash(latitude, longitude float64, precision int) string {
isEven := true
lat := []float64{-90, 90}
lng := []float64{-180, 180}
bit := 0
ch := 0
var geohash bytes.Buffer
var mid float64
for geohash.Len() < precision {
if isEven {
mid = (lng[0] + lng[1]) / 2
if longitude > mid {
ch |= bits[bit]
lng[0] = mid
} else {
lng[1] = mid
}
} else {
mid = (lat[0] + lat[1]) / 2
if latitude > mid {
ch |= bits[bit]
lat[0] = mid
} else {
lat[1] = mid
}
}
isEven = !isEven
if bit < 4 {
bit++
} else {
geohash.WriteByte(base32[ch])
bit = 0
ch = 0
}
}
return geohash.String()
}
func refineInterval(interval []float64, cd, mask int) []float64 {
if cd&mask > 0 {
interval[0] = (interval[0] + interval[1]) / 2
} else {
interval[1] = (interval[0] + interval[1]) / 2
}
return interval
}