Just to add to what has been said before, the surface connections are sometimes defined in terms of G (G1, G2 .. ) or C (C1, C2 ..)
With G only the directions of the vectos need to match, ie for G1, the tangent vectors between the two surface patches will point in the same direction. For C1, both the direction and value of the vectors need to be the same.
For the naked eye, it is difficult to make out the difference between the G and C continuities.
If you are from around Detroit, you will also hear about Class A or Class B surfacing. Class A , used on Outer Body panels, is Curvature countinious and Class B is just Tangent countinious. I still havent figured out whether it refers to G or C countinuity !!!!.
Bottom line is, in shaded mode, if you cant figure out where one surface ends and the other one starts, that is Curvature countinuity, if you see a sheen line (think of a radiused edge) it is tangent.
Hope that helps
Suresh Pillai
First Technology Safety Systems
