calculate distance in meters between two given location point

latlng_distance.go

package main

import (
    "math"
)

const (
	RAD_FACTOR   = math.Pi / 180.0
	EARTH_RADIUS = 6371000
)

func FloatEquals(fa, fb float64) bool {
	return math.Abs(fa-fb) < 0.000001
}

// Calculate the distance in meters between two given location point
func Distance(lat1, lng1, lat2, lng2 float64) int {
	if FloatEquals(lat1, lat2) && FloatEquals(lng1, lng2) {
		return 0
	}

	lat1 *= RAD_FACTOR
	lng1 *= RAD_FACTOR
	lat2 *= RAD_FACTOR
	lng2 *= RAD_FACTOR

	distance := math.Acos(math.Sin(lat1)*math.Sin(lat2) + math.Cos(lat1)*math.Cos(lat2)*math.Cos(lng2-lng1))

	return int(distance * EARTH_RADIUS)
}

func main() {
	lat := 28.418101
	lng := 119.060573

	lat1 := 29.418101
	lng1 := 120.34423
	
	fmt.Println(Distance(lat, lng, lat1, lng1)) // output: 167251
}