geo distance.lua

local geo = {}
-- ~radius of the earth in miles
geo.radius = 3958.75587

-- miles between point a and point b
function geo.distance(lat1, lng1, lat2, lng2)
  local rlat = lat1*math.pi/180;
  local rlng = lng1*math.pi/180;
  local rlat2 = lat2*math.pi/180;
  local rlng2 = lng2*math.pi/180;

  if (rlat == rlat2 and rlng == rlng2) then
    return 0
  else
    -- Spherical Law of Cosines
    return geo.radius*math.acos(math.sin(rlat)*math.sin(rlat2)
      +math.cos(rlng-rlng2)*math.cos(rlat)*math.cos(rlat2))
  end
end