Haversine [Go]

haversine.go

package main

import "fmt"
import "math"

type Vertex struct {
	Lat, Long float64
}

var m = map[string]Vertex{
	"Bell Labs":{40.68433, -74.39967},
	"Google":{37.42202, -122.08408},
}

func main() {
	fmt.Println(m)
	fmt.Printf("Distance: %fm", haversine(m["Bell Labs"], m["Google"]))
}

func toRadians(deg float64) float64 {
  return deg * math.Pi / 180.0
}

func haversine(v1 Vertex, v2 Vertex) float64 {

  R := 6371e3 // Earth mean radius in meters
  ɸ1 := toRadians(v1.Lat)
  ɸ2 := toRadians(v2.Lat)
  
  Δɸ := toRadians(v2.Lat - v1.Lat)
  Δλ := toRadians(v2.Long - v1.Long)
  
  a := math.Sin(Δɸ/2) * math.Sin(Δɸ/2) +
  	math.Cos(ɸ1) * math.Cos(ɸ2) *
	math.Sin(Δλ/2) * math.Sin(Δλ/2)
	
  c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
  
  return R * c
}