gistfile1.txt

//! Earth radius
static const double EARTH_RADIUS = 6371400;


//! convert degrees to radians
double toRad(double degrees)
{
    return M_PI / 180 * degrees;
}


//! convert radians to degrees
double toDeg(double rads)
{
    return 180 / M_PI * rads;
}


//! get distance between two points in lat/lon format (in degrees)
double distance(double lat1, double lon1,
                double lat2, double lon2)
{
    double dLat = toRad(lat2 - lat1);
    double dLon = toRad(lon2 - lon1);

    lat1 = toRad(lat1);
    lat2 = toRad(lat2);

    dLat = sin(0.5 * dLat);
    dLon = sin(0.5 * dLon);

    double a = dLat * dLat + dLon * dLon * cos(lat1) * cos(lat2);
    double c = 2 * atan2(sqrt(a), sqrt(1 - a));
    return EARTH_RADIUS * c;
}