PNORMS: platonic derived normals for error bound compression

  • Authors:

  • João Fradinho Oliveira;Bernard Francis Buxton

  • Affiliations:

  • University College London, Gower Street, London, UK;University College London, Gower Street, London, UK

  • Venue:
  • Proceedings of the ACM symposium on Virtual reality software and technology
  • Year:
  • 2006

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Abstract

3D models of millions of triangles invariably repeatedly use the same 12-byte unit normals. Several bit-wise compression algorithms exist for efficient storage and progressive transmission and visualization of normal vectors. However such methods often incur a reconstruction time penalty which, in the absence of dedicated hardware acceleration, make real-time rendering with such compression/reconstruction methods prohibitive. In particular, several methods use a subdivided octahedron to create look-up normals, where the bit length of normal indices varies according to the number of subdivisions used. Not much attention has been given to the error in the normals using such schemes. We show that different Platonic solids create different amounts of normals for each subdivision or bit length in bit-wise compression terms, with different distributions and associated errors. In particular we show that subdividing the icosahedron gives a smaller maximum and mean error than its counterparts Platonic solids. This result has led us to create an alternative to bit-wise compression of normal ids for real-time rendering, where we use a x5 subdivided icosahedron to create 2.5 times more normals than a x5 subdivided octahedron, with less error, and exploit the advantages of absolute normal indices that do not require reconstruction at run-time, whilst still having memory savings of over 83% when using 2-byte indices.We present results using 2-byte indices for a target max error of 1.3° degrees and 4-byte for a max error of