Ruby 版根据经纬度计算距离

ER = 6378137.0
FL = 1/298.257;

def rad(d) 
    d * Math::PI / 180.0
end

def calc_distance(lat1, lng1, lat2, lng2)
	cl1 = rad((lat1 + lat2)/2)
	cl2 = rad((lat1 - lat2)/2)
	cl = rad((lng1 - lng2)/2)

    	scl1 = Math.sin(cl1) ** 2
   	scl2 = Math.sin(cl2) ** 2
   	scl = Math.sin(cl) ** 2

	s = scl2 * (1 - scl) + (1 - scl1) * scl
    	c = (1 - scl2) * (1 - scl) + scl1 * scl
	w = Math.atan(Math.sqrt(s / c))
	r = Math.sqrt(s * c) / w;
	d = 2 * w * ER;
	
	h1 =  (3 * r - 1) / 2 / c
    	h2 = (3 * r + 1) / 2 / s;
    	s = d * (1 + FL * (h1 * scl1 * (1 - scl2) - h2 * (1 - scl1) * scl2));
	
	puts '> 99km' if s > 99000
	s
end