DXF doesn't include smoothing info. Converters like 3DWin can let you specify
an arbitrary smoothing threshold, but the smoothing is then done based on the
shape of the mesh; it is in no way specified in the DXF file. The 3DS format
has special "smoothing groups" which let you specify different smoothing
thresholds for different parts of the mesh, but I know of no converters that
can produce plain/smooth POV triangles based on this.
If you want all triangles to be smooth, specify a smoothing angle of 180
degrees in 3DWin. If you want a sharp edge above the smoothing threshold,
you're in trouble :)

Margus

John M. Dlugosz wrote:
> 
> But does the face info include normals?  That is, is one "face" a plain
> triangle (three points) or a smooth triangle (three points and three
> normals, as in POV and OpenGL)?  For that matter, how do mesh-based editing
> programs define such things?  I see a mesh of triangles, but how does it
> know those approximate real surfaces?  Or are they just facets, period, and
> it uses the joining angle idea like the import setting you told me about, to
> smooth things implicitly (which would make it difficult to represent a sharp
> edge that is below the critical angle!)
> 
> 'learning,
> --John

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