import math

PI =  math.pi
sin = math.sin
cos = math.cos
sqrt = math.sqrt
asin = math.asin

def deg2rad(degrees):
	return(degrees * PI / 180.0)	

def rad2deg(radians):
	return(radians * 180.0 / PI)

def sqr(num):
	return(num * num)

#def distance(latitude_1, longitude_1, latitude_2, longitude_2):
def distance(pos0, pos1):
	#(latitude_1, longitude_1) = pos0
	#(latitude_2, longitude_2) = pos1
	(longitude_1, latitude_1) = pos0
	(longitude_2, latitude_2) = pos1

	if (latitude_1 == latitude_2) and (longitude_1 == longitude_2):
		return(0.0)

	cos_latitude1 = cos (deg2rad (latitude_1))
	sin_latitude1 = sin (deg2rad (latitude_1))
	cos_latitude2 = cos (deg2rad (latitude_2))
	sin_latitude2 = sin (deg2rad (latitude_2))
 
	sin_hdlatitude = sin (deg2rad (0.5 * (latitude_1 - latitude_2)))
	sin_hdlongitude = sin (deg2rad (0.5 * (longitude_1 - longitude_2)))
	sin_dlongitude = sin (deg2rad (longitude_1 - longitude_2))

	sin_hdist_sq = sqr (sin_hdlatitude) + cos_latitude1 * cos_latitude2 * sqr (sin_hdlongitude)
	distance_rad = 2.0 * asin (sqrt (sin_hdist_sq))
	return(60.0 * rad2deg (distance_rad))