CAS (Class-A-Surface)

Surface A refers to the Class A surface. It is often said in car design

This is an extremely important concept in the field of car design and is an essential skill for car designers and A-designers.

CAS refers to a surface with very high quality. The intuitive visual expression of the quality of a surface is that it is very smooth, without wrinkles and unreasonable discontinuities.

Mathematically speaking, CAS refers to a surface with G2 level continuity between each facet and a radius of curvature jump less than a certain value. G2 continuous is a must, but the requirements for curvature jump vary from car manufacturer to car manufacturer. Among them, GM's requirement is relatively low, which is 0.05mm, followed by Toyota's, which is 0.03mm. BMW and VW's requirements are the highest, reaching 0.02mm.

Generally, the curved surfaces of cars are extremely complex. If you look in my space, you should be able to find the Alias ??wireframe diagram of a car I made. You can see that some large curved surfaces are definitely not formed all at once. Instead, it is divided into many small faces and put together, so the connection between the surfaces is extremely important. This is the requirement of continuity. However, after the continuity requirement is met, there is still a radius jump. If the radius jump is too large, the results from zebra pattern detection and environmental reflection detection will be S lines and wrinkles, which looks very unpleasant. Therefore, the A side needs to be simple, direct, and smooth. Generally, there are no more than 6 horizontal and vertical CVs, that is, U and V are both the highest D5 level curves.

The technical requirements for doing A are extremely high. Without a certain understanding of computer graphics and long-term experience in NURBS modeling, it is impossible to do it. The core of it is faceting. How to divide the surface is the easiest way. To achieve the effect, because many cars have not the four-sided structure of the standard NURBS surface but three, five or even six sides, this requires very high faceting skills and is also the focus of the Alias ??L3 designer's assessment. Many freshmen and sophomores are confident that they want to make cars, but only a few actually enter the automotive industry in their senior years. Most of them are scared away by this A-class curved surface construction.