ref: dd78ecf99a5a618f9eb0f7d4332adba8d6e39da0
server/geo/distances.go
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package geo import "math" type coordinate struct { lat float64 lon float64 } // 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 func Distance(coordinate1, coordinate2 coordinate) float64 { // convert to radians // must cast radius as float to multiply later var la1, lo1, la2, lo2, r float64 la1 = coordinate1.lat * math.Pi / 180 lo1 = coordinate1.lon * math.Pi / 180 la2 = coordinate2.lat * math.Pi / 180 lo2 = coordinate2.lon * math.Pi / 180 r = 6378100 // Earth radius in meters // calculate h := hsin(la2-la1) + math.Cos(la1)*math.Cos(la2)*hsin(lo2-lo1) return 2 * r * math.Asin(math.Sqrt(h)) } |