#include <stdio.h>
#include <math.h>
/* ------------------------------------------------------------
Convert degrees to radians
------------------------------------------------------------ */
double degToRad(double deg) {
return deg * M_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.
------------------------------------------------------------ */
double haversine(double lat1, double lon1, double lat2, double lon2) {
/* Earth's mean radius in kilometers */
const double R = 6371.0;
/* Convert all angles to radians */
double rlat1 = degToRad(lat1);
double rlon1 = degToRad(lon1);
double rlat2 = degToRad(lat2);
double rlon2 = degToRad(lon2);
/* Differences */
double dlat = rlat2 - rlat1;
double dlon = rlon2 - rlon1;
/* Haversine formula */
// a is the Haversine of the central angle between the two points.
// It combines the differences in latitude and longitude, adjusted by
// cosine terms to account for Earth’s curvature.
double a = sin(dlat / 2) * sin(dlat / 2) +
cos(rlat1) * cos(rlat2) *
sin(dlon / 2) * sin(dlon / 2);
// c is the central angle between the two points on the Earth’s surface.
// This angle is measured in radians.
// It tells you how large the arc is between the two points on the globe.
double c = 2 * asin(sqrt(a));
/* Final distance */
return R * c;
}
int main() {
/* Example coordinates:
Austin, Texas */
double lat1 = 30.2672;
double lon1 = -97.7431;
/* Houston, Texas */
double lat2 = 29.7604;
double lon2 = -95.3698;
double distanceKm = haversine(lat1, lon1, lat2, lon2);
/* Convert kilometers to miles */
double distanceMiles = distanceKm * 0.621371;
printf("Distance: %.3f km\n", distanceKm);
printf("Distance: %.3f miles\n", distanceMiles);
return 0;
}
/*
run:
Distance: 235.352 km
Distance: 146.241 miles
*/
