haversine.go

package main

import( "fmt"
        "math" )

const x = math.Pi/180
const R = 6371

// robpike: https://twitter.com/mattfarina/status/344151151719104512

func Rad(d float64) float64 {
  return d*x  
}
func Deg(r float64) float64 {
  return r/x  
}
 
func haversineDistance( lat1 float64, lon1 float64, lat2 float64, lon2 float64 ) float64 {

  dLat := Rad((lat2-lat1))
  dLon := Rad((lon2-lon1))
  lat1 = Rad(lat1)
  lat2 = Rad(lat2)

  a := math.Sin(dLat/2) * math.Sin(dLat/2) + math.Sin(dLon/2) * math.Sin(dLon/2) * math.Cos(lat1) * math.Cos(lat2)

  c := 2* math.Atan2(math.Sqrt(a), math.Sqrt(1-a))

  d := R * c

  return d
}
 
func main() {
  d := haversineDistance( -25.275890866265033, -57.51298248767853, -25.27522144836632, -57.515568137168884 )
  fmt.Println(d)
}