/**
* Calculate the distance in Km
* Sourced from StackOverflow (https://stackoverflow.com/questions/27928/calculate-distance-between-two-latitude-longitude-points-haversine-formula)
* This is the 'fastest' algorithm apparently
* 
* @param lat1 
* @param lon1 
* @param lat2 
* @param lon2 
* @returns number The distance in km
*/

export function getDistanceFromLatLonInKm(
 lat1: number,
 lon1: number,
 lat2: number,
 lon2: number
): number {
 var p = 0.017453292519943295; // Math.PI / 180
 var c = Math.cos;
 var a =
   0.5 -
   c((lat2 - lat1) * p) / 2 +
   c(lat1 * p) * c(lat2 * p) * (1 - c((lon2 - lon1) * p)) / 2;

 return 12742 * Math.asin(Math.sqrt(a)); // 2 * R; R = 6371 km
}