    0.         -1000.             upper surface
18000.         0.
    1.      -99999.               end of upper surface
    0.         600.               interface 1
18000.         100.               ...
    1.      -99999.               end of interface 1
    0.        3000.               interface 2
 3000.        3000.               ...
 6000.        3750.
10000.        3000.
15000.        2900.
18000.        2800.
    1.      -99999.               end of interface 2
