Swift wrapper for Charles Karney's C library for geodesics. See Karney's GeographicLib project, the C library for the geodesics contains the direct and inverse solver as part of the Legacy C code folder.

The shortest path between two points (p1 & p2) on the ellipsoid having locations specified by p1 at (lat1, lon1) and p2 at (lat2, lon2) is called the geodesic. Its length between p1 and p2 is s12 and the geodesic from p1 to p2 has forward azimuths az1 and az2 at the two end points.

Traditionally two geodesic problems are considered, direct and inverse.

Given lat1, lon1, s12, az1, determine lat2, lon2, and az2. This is solved by the function direct().

Example: Starting at New York JFK airport (lat=40.63972222, lon=-73.77888888), head on an initial bearing of 51.37288858° for a distance on 5,554,344m - compute the location of p2 and final forward azimuth on the WGS84 ellipsoid.

import SwiftyGeodesic
let dirResult = direct(p1: (lat: 40.63972222, lon: -73.77888888), az1: 51.37287886, s12: 5554344.26)
let p2Lat = dirResult.lat2         // 51.477500002 - lat of London Heathrow (LHR) airport
let p2Lon = dirResult.lon2         // -0.461388897 - lon of London Heathrow (LHR) airport
let p2FwdAzimuth = dirResult.az2   // 107.97130748 - forward bering at LHR

Given lat1, lon1, lat2, lon2, determine s12, az1, and az2. This is solved by the function inverse().

Example: Starting at New York JFK airport (lat=40.63972222, lon=-73.77888888) and ending at London Heathrow airport (lat=51.4775, lon=-0.46138888) - compute distance s12 and forward azimuths az1 and az2 on the WGS84 ellipsoid.

import SwiftyGeodesic
let invResult = inverse(p1: (lat: 40.63972222, lon: -73.77888888), p2: (lat: 51.4775, lon: -0.46138888))
let dist = invResult.s12          // 5554344.26   - dist between JFK to LHR
let p1FwdAzimuth = invResult.az1  // 51.37287886  - forward bearing at JFK
let p2FwdAzimuth = invResult.az2  // 107.97130749 - forward bering at LHR

dependencies: [
        .package(url: "https://github.com/firecrestHorizon/SwiftyGeodesic.git", from: "1.0.0"),
    ],

The package will use WGS84 as the default datum (semi-major axis, a = 6,378,137.0 m; flattening f = 1/298.257223563) Other ellipsoids can be used by overrding the default ellipsoid a & f values.

Example for ETRS89:

let ETRS89 = (a: 6378137.0, f: 1 / 298.257222101)
let dirResult = direct(p1: (lat: 51.21, lon: 3.456), az1: 23.344, s12: 10000, ellipsoid: ETRS89)