112 lines
2.1 KiB
Go
112 lines
2.1 KiB
Go
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// Copyright © 2016 Abcum Ltd
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package geof
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import (
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"bytes"
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"github.com/abcum/surreal/sql"
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)
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var bits = []int{16, 8, 4, 2, 1}
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var latmax = []float64{-90, 90}
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var lngmax = []float64{-180, 180}
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var base32 = []byte("0123456789bcdefghjkmnpqrstuvwxyz")
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func refine(interval []float64, cd, mask int) []float64 {
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if cd&mask > 0 {
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interval[0] = (interval[0] + interval[1]) / 2
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} else {
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interval[1] = (interval[0] + interval[1]) / 2
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}
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return interval
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}
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func GeohashDecode(hash string) *sql.Point {
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isEven := true
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lat := latmax
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lng := lngmax
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latErr := float64(90)
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lngErr := float64(180)
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var c string
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var cd int
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for i := 0; i < len(hash); i++ {
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c = hash[i : i+1]
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cd = bytes.Index(base32, []byte(c))
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for j := 0; j < 5; j++ {
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if isEven {
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lngErr /= 2
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lng = refine(lng, cd, bits[j])
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} else {
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latErr /= 2
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lat = refine(lat, cd, bits[j])
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}
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isEven = !isEven
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}
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}
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return sql.NewPoint(
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(lat[0]+lat[1])/2,
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(lng[0]+lng[1])/2,
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)
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}
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func GeohashEncode(point *sql.Point, precision int64) string {
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isEven := true
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lat := []float64{-90, 90}
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lng := []float64{-180, 180}
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bit := 0
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ch := 0
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var geohash bytes.Buffer
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var mid float64
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for geohash.Len() < int(precision) {
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if isEven {
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mid = (lng[0] + lng[1]) / 2
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if point.LO > mid {
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ch |= bits[bit]
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lng[0] = mid
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} else {
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lng[1] = mid
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}
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} else {
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mid = (lat[0] + lat[1]) / 2
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if point.LA > mid {
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ch |= bits[bit]
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lat[0] = mid
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} else {
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lat[1] = mid
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}
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}
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isEven = !isEven
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if bit < 4 {
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bit++
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} else {
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geohash.WriteByte(base32[ch])
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bit = 0
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ch = 0
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}
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}
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return geohash.String()
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}
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