beziersurf bsurf_r 3 4  0 0 0 1  10 0 5 1  20 0 0 1  0 10 2 1  10 10 3 1  20 10 2 1  0 20 10 1  10 20 20 1  20 20 10 1  0 30 0 1   10 30 0 1   20 30 0 1
trim r bsurf_r 0.5 0.8 0.5 0.8
set MaxFTol 9.9999999999999995e-08
set MaxETol 9.9999999999999995e-08
set MaxVTol 9.9999999999999995e-08