'Class A surface' is a term in the automotive design industry, describing spline surfaces with aesthetic, non-oscillating highlight lines. Tensor-product B-splines of degree bi-3 (bicubic) are routinely used to generate smooth design surfaces and are often the de facto standard for downstream processing. To bridge the gap, this paper explores and gives a concrete suggestion, how to achieve good highlight line distributions for  irregular  bi-3 tensor-product patch layout by allowing, along some seams, a slight mismatch of normals below the industry-accepted tolerance of one tenth of a degree. Near the irregularities, the solution can be viewed as transforming a higher-degree, high-quality formally smooth surface into a bi-3 spline surface with few pieces, sacrificing formal smoothness but qualitatively retaining the shape.
['Kestutis Karciauskas', 'Jörg Peters']
Can bi-cubic surfaces be class A?