us of a reference spheroid.  This 
              spheroid is a volume of revolution:  its horizontal 
              cross sections are circular.  The shape of the 
              spheroid is defined by an equatorial radius `re' and 
              a polar radius `rp'.  Units of `re' must match those of  
              `alt'. 
 
   f          Flattening coefficient =  
 
                 (re-rp) / re 
 
              where `rp' is the polar radius of the spheroid, and the 
              units of `rp' match tho