#include <iostream>
#include <cmath>
// ------------------------------------------------------------
// 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
constexpr 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 = std::sin(dlat / 2) * std::sin(dlat / 2) +
std::cos(rlat1) * std::cos(rlat2) *
std::sin(dlon / 2) * std::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 * std::asin(std::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;
std::cout << "Distance: " << distanceKm << " km\n";
std::cout << "Distance: " << distanceMiles << " miles\n";
}
/*
run:
Distance: 235.352 km
Distance: 146.241 miles
*/
