# Distinguish between one surface and two surface with G2 continuity in car surface

Hi dears i have a question
If i want modeling a car:
How can i distinguish between one surface and two surfaces with G2 continuity in the real car? i tried to find out with reflection of the car’s surfaces but i didn’t get any result.

That’s the point of a G2 curvature continuous edge; to not see the edge in a reflection.
A G0 position match reflection will show a reflection breaking and exiting the common edge in a different location.
A G1 tangent edge will show a sharp kink in the reflection at the edge but no shifting of the reflection.
A G2 curvature continuous edge will show a smooth transition with no kink or break in the reflection over the seam.
Higher degree matching will effect the smooth blend of one reflection into the other.

Thanks for your attention and i’m sorry for my delay
What i mean : is there any way to distinguish between one surface and two surfaces with G2 continuity in the real car not in the rhino software

With G2 continuity (or higher), the surface edges have no break or sharp
crease in the reflection, so they disappear and can not be seen.

J Brock

On a real car you could say it is all G2 continuity.
In formed and painted sheet metal, it is not possible to create
G1 continuity even if you wanted it to be there.

I would say, if it is done at all right, no, there is no way to tell where the digital surfaces connect in the final product…

-Pascal

Look at reflections of building edges, cables, wires, etc. on the real car surface. If the car is inside look at fluorescent lamp reflections. If the reflections or curves have “kinks” then the surfaces are G1. If the reflections are discontinuous the surfaces are G0. Reflections can reveal a lot about surfacing.

Correct for stamped metal. However the the sheet metal may have changes of curvature which occur in a very short distance to be close to G1, or a small radius fillet to be close to G0. Molded plastic can be G1 or G0.

Only if the design intent is G2 or better continuity between the surfaces.

Thanks a lot for your attention my friends

Do you mean something like Rhino’s networkSrf likes to make?

Maybe, if you don’t look too closely or carefully. In the real world there are no perfectly sharp corners and no perfect transitions in curvature.
Even in Rhino where sudden changes in curvature are possible , that doesn’t mean you will always be able to see the sudden curvature transitions. None of the surfaces in this file are matched for curvature, but try to to find the seams with Zebra analysis.

zebra.3dm (393.0 KB)

well you have to look very hard