[snip]
>     <11, amp*10*sin(radians(180+clock*(360/fr))), 0>, ......
>     <12, amp*10*sin(radians(195+clock*(360/fr))), 0>, ......
>   }
>   bicubic_patch
>   {
>     type 0 flatness 0.01 u_steps 4 v_steps 4
>     <12, amp*10*sin(radians(195+clock*(360/fr))), 0>,  ......
>     <13, amp*10*sin(radians(210+clock*(360/fr))), 0>,  ......
[snip]

basically what you are assuming here is that sin() is a linear function
i.e. that the midpoint between sin(x) and sin(x+delta) is
sin(x+delta/2) and unfortunately it isn't.

This part should be:

     <11, amp*10*sin(radians(180+clock*(360/fr))), 0>, ......
     <12, 
amp*10*(sin(radians(180+clock*(360/fr)))+sin(radians(210+clock*(360/fr))))/2, 
0>,  ......
   }
   bicubic_patch
   {
     type 0 flatness 0.01 u_steps 4 v_steps 4
     <12, 
amp*10*(sin(radians(180+clock*(360/fr)))+sin(radians(210+clock*(360/fr))))/2, 
0>,  ......
     <13, amp*10*sin(radians(210+clock*(360/fr))), 0>,  ......

(I hope I did not miscount this lots of stupid parenteses)

Though I would prefer a somewhat less verbose version ;)

BTW in this case it might not be a problem, but sometimes it is better
to take the used control points equidistant and the interpolated points
at half a distance. Not sure if I am clear, lets try an ASCII drawing:

0---*---*-+-*---*-+-*---*-+-*---*-+-*---*---0

where 0,*, and + are control points for first line of the 5 bicubic
patches. For the total flag the 0 are the endpoints, * the middle
control points and + the points where two bicubic patches meet.

I really hope it is clearer now, but it might just confuse more :( .

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