The german term „Strak“ (in English: Class A-surface) has its origins in the ship building where complicated free form surfaces were described with vertical, longitudinal and cross sections (frames). In the automotive sector this method was adapted for the generation of all non-planar free form surfaces in the exterior and interior work. Before CA-tools came into play design surfaces were based on so-called „sections“ which reflect the main curves (character lines).
For the last 20 years we have been generating surfaces with the help of CA-tools. In this context, the software „ICEM-Surf“ established itself to be the standard tool for surfacing, where different analysis methods like highlights, isometric lines as well as curvature guarantee the surface quality in real time.
Class A-surfaces are the conversion of styling data into technically realizable surfaces.
When we talk of CATIA V4, the styling data related component design process is a nearly serial one. In given cycles the surfacers are provided with styling data. Here the surfaces are designed and passed on to the component designers. In any case, I don´t want you to get the impression that these jobs were not done simultaneously.
But in a non-associative process like in CATIA V4, the surfaces subject to changes have to be redesigned in the following process. In an associative process CATIA V5 can assume many operations of the work flow in case of modifications or enables the component designer to work on assumptions at a certain time. Furthermore, he can work with substitute geometry if a certain maturity of data does not yet exist.