// ------------------------------------------------------------
// Convert degrees to radians
// ------------------------------------------------------------
function degToRad(deg) {
return deg * Math.PI / 180.0;
}
// ------------------------------------------------------------
// Compute the great-circle distance between two points on Earth
// using the Haversine formula.
// lat1, lon1, lat2, lon2 are in degrees.
// The result is returned in kilometers.
// ------------------------------------------------------------
function haversine(lat1, lon1, lat2, lon2) {
// Earth's mean radius in kilometers
const R = 6371.0;
// Convert all angles to radians
const rlat1 = degToRad(lat1);
const rlon1 = degToRad(lon1);
const rlat2 = degToRad(lat2);
const rlon2 = degToRad(lon2);
// Differences
const dlat = rlat2 - rlat1;
const dlon = rlon2 - rlon1;
// Haversine formula
// a is the Haversine of the central angle between the two points.
const a =
Math.sin(dlat / 2) ** 2 +
Math.cos(rlat1) * Math.cos(rlat2) *
Math.sin(dlon / 2) ** 2;
// c is the central angle between the two points on the Earth’s surface.
const c = 2 * Math.asin(Math.sqrt(a));
// Final distance
return R * c;
}
// ------------------------------------------------------------
// Main
// ------------------------------------------------------------
// Example coordinates:
// Austin, Texas
const lat1 = 30.2672;
const lon1 = -97.7431;
// Houston, Texas
const lat2 = 29.7604;
const lon2 = -95.3698;
const distanceKm = haversine(lat1, lon1, lat2, lon2);
// Convert kilometers to miles
const distanceMiles = distanceKm * 0.621371;
console.log(`Distance: ${distanceKm.toFixed(3)} km`);
console.log(`Distance: ${distanceMiles.toFixed(3)} miles`);
/*
run:
Distance: 235.352 km
Distance: 146.241 miles
*/
