Posted by 3DOXprt on February 10, 1998 at 15:18:37:
In Reply to: Hey, 3DOXprt... face normals! posted by fiXXXer on February 10, 1998 at 11:03:05:
> Hi there.
> Are face normals calculated?or does 3do converter just guess them? (I hope it doesn't) =P
> Now, serious... i've found that the face normals in 3do converter are always messed up and after inverting some of them "by hand" all face-disappearing models i had worked correctly.
> And what are face flags for?
They are most certainly not "guessed" at! :-) A face normal describes the orientation of the plane made by the face to the origin. They are are the A,B,C coefficients of Ax+By+Cz+D=0. If they are pointing the wrong way, then your faces are declared in the wrong order. The equations 3DO Converter use are correct. I tested this by loading models, recomputing the normals and comparing them to the original models. They were always within 0.000001, which is an acceptable epsilon value. If you know you declared them in the wrong order, then you can choose to invert the normals. Vertex normals are just the average of the face normals of the faces that reference that vertex.
Talk to the meddle auther if that's what program you're using and tell him to reverse his declaration of faces when outputting to ASC.
Face flags serve the same purpose as face flags in JED, they simply add properties to the faces.