TypeScript - distance between points on the Earth in km

interface Coordinates {

    lat: number;

    lon: number;

}

​

const RADIAN: number = Math.PI / 180.0;

const RADIUS: number = 6371; // earth radius in km (https://dirask.com/posts/Constants-Earth-radius-in-km-p2YMAD)

const DIAMETER: number = 2 * RADIUS;

​

const toRadians = (degrees: number): number => {

    return RADIAN * degrees;

};

​

// Calcultes distance from a to b points in km (a and b variables should be provided in radians).

//

const calculateDistance$1 = (a: Coordinates, b: Coordinates): number => {

    const dLat = b.lat - a.lat;

    const dLon = b.lon - a.lon;

    const aTmp = Math.sin(0.5 * dLat);

    const bTmp = Math.sin(0.5 * dLon);

    const cTmp = aTmp * aTmp + bTmp * bTmp * Math.cos(a.lat) * Math.cos(b.lat);

    return DIAMETER * Math.atan2(Math.sqrt(cTmp), Math.sqrt(1.0 - cTmp));

};

​

// Calcultes distance from a to b points in km (a and b variables should be provided in degrees).

//

const calculateDistance$2 = (a: Coordinates, b: Coordinates): number => {

    const aTmp = { lat: toRadians(a.lat), lon: toRadians(a.lon) };

    const bTmp = { lat: toRadians(b.lat), lon: toRadians(b.lon) };

    return calculateDistance$1(aTmp, bTmp);

};

​

​

// Usage example:

​

const a: Coordinates = { lat: 51.528308, lon: -0.3817765 }; // London City (United Kingdom)

const b: Coordinates = { lat: 40.6974034, lon: -74.1197612 }; // New York City (USA)

​

const distance: number = calculateDistance$2(a, b);

​

console.log(distance); // ~5561.352931973071 [km]

5561.352931973071