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forgejo/vendor/github.com/blevesearch/bleve/geo/geohash.go
2019-11-27 11:23:33 +02:00

111 lines
2.6 KiB
Go
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// Copyright (c) 2019 Couchbase, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// This implementation is inspired from the geohash-js
// ref: https://github.com/davetroy/geohash-js
package geo
// encoding encapsulates an encoding defined by a given base32 alphabet.
type encoding struct {
enc string
dec [256]byte
}
// newEncoding constructs a new encoding defined by the given alphabet,
// which must be a 32-byte string.
func newEncoding(encoder string) *encoding {
e := new(encoding)
e.enc = encoder
for i := 0; i < len(e.dec); i++ {
e.dec[i] = 0xff
}
for i := 0; i < len(encoder); i++ {
e.dec[encoder[i]] = byte(i)
}
return e
}
// base32encoding with the Geohash alphabet.
var base32encoding = newEncoding("0123456789bcdefghjkmnpqrstuvwxyz")
var masks = []uint64{16, 8, 4, 2, 1}
// DecodeGeoHash decodes the string geohash faster with
// higher precision. This api is in experimental phase.
func DecodeGeoHash(geoHash string) (float64, float64) {
even := true
lat := []float64{-90.0, 90.0}
lon := []float64{-180.0, 180.0}
for i := 0; i < len(geoHash); i++ {
cd := uint64(base32encoding.dec[geoHash[i]])
for j := 0; j < 5; j++ {
if even {
if cd&masks[j] > 0 {
lon[0] = (lon[0] + lon[1]) / 2
} else {
lon[1] = (lon[0] + lon[1]) / 2
}
} else {
if cd&masks[j] > 0 {
lat[0] = (lat[0] + lat[1]) / 2
} else {
lat[1] = (lat[0] + lat[1]) / 2
}
}
even = !even
}
}
return (lat[0] + lat[1]) / 2, (lon[0] + lon[1]) / 2
}
func EncodeGeoHash(lat, lon float64) string {
even := true
lats := []float64{-90.0, 90.0}
lons := []float64{-180.0, 180.0}
precision := 12
var ch, bit uint64
var geoHash string
for len(geoHash) < precision {
if even {
mid := (lons[0] + lons[1]) / 2
if lon > mid {
ch |= masks[bit]
lons[0] = mid
} else {
lons[1] = mid
}
} else {
mid := (lats[0] + lats[1]) / 2
if lat > mid {
ch |= masks[bit]
lats[0] = mid
} else {
lats[1] = mid
}
}
even = !even
if bit < 4 {
bit++
} else {
geoHash += string(base32encoding.enc[ch])
ch = 0
bit = 0
}
}
return geoHash
}