geo

Geodetic calculations on the sphere (1.27.0): great-circle distance, initial bearing, midpoint, and destination point. All coordinates are in decimal degrees. Distances use a mean Earth radius of 6371 km.

import geo;

let d = geo.haversineDistance(51.5074, -0.1278, 48.8566, 2.3522);
io.println("${d} km");   /* ~343.56 km (London to Paris) */

Functions

haversineDistance

geo.haversineDistance(lat1, lon1, lat2, lon2, unit?)

Returns the great-circle distance between two points using the Haversine formula. lat1, lon1, lat2, lon2 are in decimal degrees. unit is an optional string defaulting to "km".

geo.haversineDistance(51.5074, -0.1278, 48.8566, 2.3522);         /* km */
geo.haversineDistance(51.5074, -0.1278, 48.8566, 2.3522, "mi");   /* miles */
geo.haversineDistance(51.5074, -0.1278, 48.8566, 2.3522, "m");    /* metres */
geo.haversineDistance(51.5074, -0.1278, 48.8566, 2.3522, "nmi");  /* nautical miles */

bearing

geo.bearing(lat1, lon1, lat2, lon2)

Returns the initial bearing in degrees (0 to 360, clockwise from north) from point 1 to point 2.

geo.bearing(51.5074, -0.1278, 48.8566, 2.3522);  /* ~148.12 degrees */

midpoint

geo.midpoint(lat1, lon1, lat2, lon2)

Returns the geographic midpoint on the great-circle path as a dict {"lat": ..., "lon": ...} in decimal degrees.

let mid = geo.midpoint(51.5074, -0.1278, 48.8566, 2.3522);
mid["lat"];   /* ~50.19 */
mid["lon"];   /* ~1.15 */

destination

geo.destination(lat, lon, bearing, distance, unit?)

Returns the destination point {"lat": ..., "lon": ...} reached by travelling distance at the given bearing (degrees, clockwise from north) from the starting point (lat, lon). unit defaults to "km".

let dest = geo.destination(51.5074, -0.1278, 90.0, 100.0);
/* point 100 km due east of London */

geo.destination(51.5074, -0.1278, 180.0, 200.0, "mi");
/* 200 miles due south */

Distance units

Error handling

• A latitude outside [-90, 90] raises RuntimeError with the message <function>: latitude must be in [-90, 90].
• An unrecognised unit string raises RuntimeError with the message geo: unknown distance unit "...".

try {
    geo.haversineDistance(91.0, 0.0, 0.0, 0.0);
} catch (RuntimeError e) {
    io.println(e.message); /* geo.haversineDistance: latitude must be in [-90, 90] */
}