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78 lines
2.2 KiB
C
78 lines
2.2 KiB
C
// This small program computes the distance between two points on the Earths
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// surface. The algorithm used for computing is called haversine formula.
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// Source for the algorithm can be found here:
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// https://en.wikipedia.org/wiki/Haversine_formula
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#include <math.h>
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#include <stdlib.h>
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#include <stdio.h>
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// Earth's radius in meters.
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#define RADIUS ((12756L / 2.0L) * 1000L)
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// PI natural constant
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#define PI 3.1415926536L
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// coordinates struct for storing points
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struct Coordinate {
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double latitude;
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double longitude;
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};
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/**
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* @brief Calculates a radian value from an angle
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*/
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double radian_from(const double angle) {
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return (angle * PI) / 180;
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}
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/**
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* @brief Calculate the haversine function from an angle in radian
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*/
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double haversine(const double angle) { return ((1.0L - cos(angle)) / 2); }
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/**
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* @brief Calculate the distance between two coordinates
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*/
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double great_circle_distance(const struct Coordinate a,
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const struct Coordinate b) {
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// calculate longitude and latitude differences
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struct Coordinate diff_coord = {
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.longitude = a.longitude - b.longitude,
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.latitude = a.latitude - b.latitude,
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};
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// calculate haversine(theta) value, where theta is the angle between the
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// two coordinates
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double hav_theta = haversine(diff_coord.latitude)
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+ cos(a.latitude) * cos(b.latitude) * haversine(diff_coord.longitude);
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// calculate distance from radius, and haversine(theta) values
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double distance = 2 * RADIUS * asin(sqrt(hav_theta));
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return distance;
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}
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int main(int argc, const char* argv[]) {
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if (argc < 5 || argc > 5) {
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return 1;
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}
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const struct Coordinate a = {
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.latitude = radian_from(atof(argv[1])),
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.longitude = radian_from(atof(argv[2])),
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};
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const struct Coordinate b = {
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.latitude = radian_from(atof(argv[3])),
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.longitude = radian_from(atof(argv[4])),
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};
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// Returns the distance in meters.
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// To pretty-print the result in a consumer of this module, it is
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// recommended to divide the result by 1,000 and round it.
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printf("%.1f\n", great_circle_distance(a, b));
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return 0;
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}
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