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// 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(lat1, lon1, lat2, lon2 float64) float64 { | |
// convert to radians | |
// must cast radius as float to multiply later | |
var la1, lo1, la2, lo2, r float64 | |
la1 = lat1 * math.Pi / 180 | |
lo1 = lon1 * math.Pi / 180 | |
la2 = lat2 * math.Pi / 180 | |
lo2 = lon2 * 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)) | |
} |
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