Efficient handling of shading discontinuities for progressive meshes

For visual perception of 3D models, shading plays one of the major roles. The shading quality of level-of-detail models is limited generally because existing LOD algorithms assume a conceptually smooth surface. A complex mesh, however, is likely to have conceptually smooth and angular parts. We introduce an extension to the progressive mesh LOD approach that efficiently handles triangle meshes with large numbers of shading discontinuities. For this, the algorithm distinguishes three principal shading situations for mesh vertices: completely continuous shading, completely discontinuous shading, and mixed continuous/discontinuous shading. Remarkably, the algorithm does not introduce any overhead for completely smooth surfaces. As one field of application, we briefly outline its application for LOD representations of 3D city models.