Visual Smoothness of Polyhedral Surfaces

Davide Pellis, Martin Kilian, Felix Dellinger, Johannes Wallner, Helmut Pottmann

Research output: Contribution to journalArticlepeer-review


Representing smooth geometric shapes by polyhedral meshes can be quite difficult in situations where the variation of edges and face normals is prominently visible. Especially problematic are saddle-shaped areas of the mesh, where typical vertices with six incident edges are ill suited to emulate the more symmetric smooth situation. The importance of a faithful discrete representation is apparent for certain special applications like freeform architecture, but is also relevant for simulation and geometric computing.

In this paper we discuss what exactly is meant by a good representation of saddle points, and how this requirement is stronger than a good approximation of a surface plus its normals. We characterize good saddles in terms of the normal pyramid in a vertex.

We show several ways to design meshes whose normals enjoy small variation (implying good saddle points). For this purpose we define a discrete energy of polyhedral surfaces, which is related to a certain total absolute curvature of smooth surfaces. We discuss the minimizers of both functionals and in particular show that the discrete energy is minimal not for triangle meshes, but for principal quad meshes. We demonstrate our procedures for optimization and interactive design by means of meshes intended for architectural design.
Original languageEnglish
Article number31
Number of pages11
JournalACM Transactions on Graphics
Issue number4
Publication statusPublished - Jul 2019


  • Smoothness
  • polyhedral surfaces
  • variation of normals
  • architectural geometry
  • total absolute curvature


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