@pranavstark/geo-distances/lib/index.js

A geographical distance calculator. Calculates distance between two points using haversine formula.

'use strict';

let radiusUnits = {
    'feet': 20908800,
    'yards': 6969600,
    'miles': 3960,
    'mi': 3960,
    'kilometers': 6371,
    'km': 6371,
    'meters': 6371000
};

class Utils {
    distance(lat1, lon1, lat2, lon2, unit) {
        let RaE = getEarthRadius(unit);
        let dLat = degreeToRadian(lat2 - lat1);
        let dLon = degreeToRadian(lon2 - lon1);
        return distance_formula(RaE, dLat, dLon, lat1, lat2);
    }
}

let degreeToRadian = (degree) => {
    return degree * (Math.PI / 180);
}

//Haversine formula
let distance_formula = (RaE, dLat, dLon, lat1, lat2) => {
    let calc1 = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
        Math.cos(degreeToRadian(lat1)) * Math.cos(degreeToRadian(lat2))
        * Math.sin(dLon / 2) * Math.sin(dLon / 2)

    let calc2 = 2 * Math.atan2(Math.sqrt(calc1), Math.sqrt(1 - calc1))
    return RaE * calc2
}

let getEarthRadius = ((unit) => {
    if (unit == null) {
        unit = "km";
    }
    unit = unit.toLowerCase();
    if (!radiusUnits[unit]) {
        unit = "km";
    }
    return radiusUnits[unit];
})


module.exports = new Utils();