open System module Earth = type Point(lon,lat) = let toRad deg = deg * (Math.PI / 180.0) member this.Lon = lon member this.Lat = lat member this.LonRad = toRad lon member this.LatRad = toRad lat let greatCircleDistance (p1:Point) (p2:Point) = // code adapted from // http://www.codeproject.com/Articles/12269/Distance-between-locations-using-latitude-and-long (* The Haversine formula according to Dr. Math. http://mathforum.org/library/drmath/view/51879.html dlon = lon2 - lon1 dlat = lat2 - lat1 a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2 c = 2 * atan2(sqrt(a), sqrt(1-a)) d = R * c Where * dlon is the change in longitude * dlat is the change in latitude * c is the great circle distance in Radians. * R is the radius of a spherical Earth. * The locations of the two points in spherical coordinates (longitude and latitude) are lon1,lat1 and lon2, lat2. *) let dlon = p2.LonRad - p1.LonRad; let dlat = p2.LatRad - p1.LatRad; // Intermediate result a. let a = (sin (dlat / 2.0)) ** 2.0 + ((cos p1.LatRad) * (cos p2.LatRad) * (sin (dlon / 2.0)) ** 2.0); // Intermediate result c (great circle distance in Radians). let c = 2.0 * (asin (sqrt a)); // Distance. let earthRadiusKms = 6371.0; let distance = earthRadiusKms * c; distance let test = let d = greatCircleDistance (new Point(5.0, -32.0)) (new Point(-3.0, 4.0)) printfn "%f" d // 4091 km