47 lines
1.4 KiB
Go
47 lines
1.4 KiB
Go
package miniredis
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import (
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"math"
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"github.com/alicebob/miniredis/v2/geohash"
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)
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func toGeohash(long, lat float64) uint64 {
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return geohash.EncodeIntWithPrecision(lat, long, 52)
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}
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func fromGeohash(score uint64) (float64, float64) {
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lat, long := geohash.DecodeIntWithPrecision(score, 52)
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return long, lat
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}
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// haversin(θ) function
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func hsin(theta float64) float64 {
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return math.Pow(math.Sin(theta/2), 2)
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}
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// distance function returns the distance (in meters) between two points of
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// a given longitude and latitude relatively accurately (using a spherical
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// approximation of the Earth) through the Haversin Distance Formula for
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// great arc distance on a sphere with accuracy for small distances
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// point coordinates are supplied in degrees and converted into rad. in the func
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// distance returned is meters
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// http://en.wikipedia.org/wiki/Haversine_formula
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// Source: https://gist.github.com/cdipaolo/d3f8db3848278b49db68
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func distance(lat1, lon1, lat2, lon2 float64) float64 {
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// convert to radians
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// must cast radius as float to multiply later
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var la1, lo1, la2, lo2 float64
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la1 = lat1 * math.Pi / 180
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lo1 = lon1 * math.Pi / 180
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la2 = lat2 * math.Pi / 180
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lo2 = lon2 * math.Pi / 180
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earth := 6372797.560856 // Earth radius in METERS, according to src/geohash_helper.c
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// calculate
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h := hsin(la2-la1) + math.Cos(la1)*math.Cos(la2)*hsin(lo2-lo1)
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return 2 * earth * math.Asin(math.Sqrt(h))
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}
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