es the interpolation appropriately by
    appending the last column of ZO to its front and the last to is back.
 
    <a href="interplatlon.html">INTERPLATLON</a> accounts for the fact that LONO may have an arbitrary 
    starting value, not necessarily -180 or 0, as its initial point, e.g.
    LONO may begin at -20 and end at 340.  Note that both LONO and LON are
    interpreted as angles on the complex plane, so the modifications
    LONO+n*360 or LON+n*360 for integer n would not change the result.  
 
 