gistfile1.rb

class DistanceCalculator

  #radians per degree
  RAD_PER_DEG = 0.017453293

  #radius of the earth, in miles
  Rmiles = 3956

  def self.get_distance(lat1, lon1, lat2, lon2)

    dlon = lon2 - lon1  
    dlat = lat2 - lat1  
    
    dlon_rad = dlon * RAD_PER_DEG   
    dlat_rad = dlat * RAD_PER_DEG  
    
    lat1_rad = lat1 * RAD_PER_DEG  
    lon1_rad = lon1 * RAD_PER_DEG  
    
    lat2_rad = lat2 * RAD_PER_DEG  
    lon2_rad = lon2 * RAD_PER_DEG  
    
    a = (Math.sin(dlat_rad/2))**2 + Math.cos(lat1_rad) * Math.cos(lat2_rad) * (Math.sin(dlon_rad/2))**2  
    c = 2 * Math.atan2( Math.sqrt(a), Math.sqrt(1-a))  
    
    (Rmiles * c).floor

  end

end

#should be 89 miles from vista to LA
puts DistanceCalculator.get_distance(33,-117,34,-118)