Hi,

How is this flat polygon supposed to be shaded curved ???

all supplied vertex normals point in the same direction.

o object1
g object1
v 0.00000000 -0.00000003 3.13267816
v 0.00000000 0.00000008 -11.46117186
v 33.88950663 0.00000008 -11.46117186
v 33.88950663 -0.00000003 3.13267816
vt 0.00000000 1.00000000
vt 0.00000000 0.00000000
vt 1.00000000 0.00000000
vt 1.00000000 1.00000000
vn 0.00000000 -0.70710678 -0.70710679
vn 0.00000000 -0.70710679 0.70710678
vn 0.00000000 -0.70710679 0.70710678
vn 0.00000000 -0.70710678 -0.70710679
s 1
f 1/1/1 2/2/2 3/3/3 4/4/4