geodesy-haversine

Great-circle geodesy on a spherical earth: distance, initial bearing, midpoint, destination point, and total path length. Dependency-free ESM.

Coordinates are { lat, lon } in decimal degrees. Distances are in kilometres by default; pass a radius to switch units.

import { distance, bearing, destination, pathLength } from 'geodesy-haversine';

const london = { lat: 51.5074, lon: -0.1278 };
const paris  = { lat: 48.8566, lon: 2.3522 };

distance(london, paris);              // ~343 km
distance(london, paris, 3958.8);      // ~213 miles (miles radius)
bearing(london, paris);               // initial azimuth, degrees

destination({ lat: 40, lon: -75 }, 90, 100); // 100 km due east
pathLength([london, paris]);          // total across a polyline

Accuracy

The haversine formula assumes a sphere. Real-world error versus an ellipsoidal model (Vincenty / WGS-84) is up to roughly 0.5%. If you need survey-grade accuracy, use an ellipsoidal solver instead. For routing, proximity, and "how far is it" answers this is plenty.

EARTH_RADIUS_KM is the WGS-84 authalic mean radius, 6371.0088.

License

This is free and unencumbered software released into the public domain (Unlicense). See LICENSE.