geo.go

package miniredis

import (
	"fmt"
	"math"

	"github.com/alicebob/miniredis/v2/geohash"
)

func toGeohash(long, lat float64) uint64 {
	return geohash.EncodeIntWithPrecision(lat, long, 52)
}

func fromGeohash(score uint64) (float64, float64) {
	lat, long := geohash.DecodeIntWithPrecision(score, 52)
	return long, lat
}

// FormatGeo format a longitude or latitude as a string, used in replies.
//
// Redis dumps the raw floating point, but we are off by a little from that
// number so we don't. The first 5 digits do match with Redis, which will do:
// https://www.xkcd.com/2170/
func formatGeo(longlat float64) string {
	return fmt.Sprintf("%.5f", longlat)
}

// haversin(θ) function
func hsin(theta float64) float64 {
	return math.Pow(math.Sin(theta/2), 2)
}

// distance function returns the distance (in meters) between two points of
//     a given longitude and latitude relatively accurately (using a spherical
//     approximation of the Earth) through the Haversin Distance Formula for
//     great arc distance on a sphere with accuracy for small distances
//
// point coordinates are supplied in degrees and converted into rad. in the func
//
// distance returned is meters
// http://en.wikipedia.org/wiki/Haversine_formula
// Source: https://gist.github.com/cdipaolo/d3f8db3848278b49db68
func distance(lat1, lon1, lat2, lon2 float64) float64 {
	// convert to radians
	// must cast radius as float to multiply later
	var la1, lo1, la2, lo2 float64
	la1 = lat1 * math.Pi / 180
	lo1 = lon1 * math.Pi / 180
	la2 = lat2 * math.Pi / 180
	lo2 = lon2 * math.Pi / 180

	earth := 6372797.560856 // Earth radius in METERS, according to src/geohash_helper.c

	// calculate
	h := hsin(la2-la1) + math.Cos(la1)*math.Cos(la2)*hsin(lo2-lo1)

	return 2 * earth * math.Asin(math.Sqrt(h))
}