//  main.c
//  Distance
//  gcc location2distance.c -lm
//

#include <stdio.h>
#include <math.h>

#define PI                      3.1415926
#define EARTH_RADIUS            6378137        // 地球近似半径 m

double radian(double d);
double get_distance(double lat1, double lng1, double lat2, double lng2);

// 求弧度
double radian(double d)
{
    return d * PI / 180.0;   //角度1˚ = π / 180
}

//计算距离
double get_distance(double lat1, double lng1, double lat2, double lng2)
{
    double radLat1 = radian(lat1);
    double radLat2 = radian(lat2);
    double a = radLat1 - radLat2;
    double b = radian(lng1) - radian(lng2);

    double dst = 2 * asin((sqrt(pow(sin(a / 2), 2) + cos(radLat1) * cos(radLat2) * pow(sin(b / 2), 2))));

    dst = dst * EARTH_RADIUS;
    dst = round(dst * 10000) / 10000;

    return dst;
}

int main(int argc, const char* argv[])
{
    double localtion1[] = { 22.562283, 113.942343 };   // 纬度1, 经度1
    double localtion2[] = { 22.562274, 113.943067 };   // 纬度2, 经度2

    double dst = get_distance(localtion1[0], localtion1[1], localtion2[0], localtion2[1]);

    printf("dst = %f m\n", dst);  // 74.433500 m

    return 0;
}