function distance(lat1, lon1, lat2, lon2) {
    const R = 6371; // 지구 반지름 (단위: km)
    const dLat = deg2rad(lat2 - lat1);
    const dLon = deg2rad(lon2 - lon1);
    const a = Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) *
        Math.sin(dLon/2) * Math.sin(dLon/2);
    const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
    const distance = R * c; // 두 지점 간의 거리 (단위: km)
    return distance;
}

function deg2rad(deg) {
    return deg * (Math.PI/180);
}