Consistent Normal Orientation for Polygonal Meshes

In proceedings of Computer Graphics International 2004 (CGI 2004), pages 18-25, IEEE Computer Society, June 2004
Presented at Computer Graphics International 2004 (CGI 2004)
 

Abstract

In many areas of computer graphics, such as real-time rendering, mesh processing, etc., models are assumed to consist of correctly oriented polygons. However, many geometric modelling tools (such as CAD systems), do not pay attention to the orientation of the normals when exporting polygonal models.

In this paper, we propose a new method that can consistently orient all normals of any mesh (if at all possible), while ensuring that most polygons are seen with their front-faces from most viewpoints. Our algorithm combines the proximity-based with a new visibility-based approach. Thus, it virtually eliminates the problems of proximity-based approaches, while avoiding the limitations of solid-based approaches.

Our new method builds a connectivity graph of the patches of the model, which encodes the "proximity" of neighboring patches. In addition, it augments this graph with two visibility coefficients for each patch. Based on this graph, a global consistent orientation of all patches is quickly found by a greedy optimization.

We have tested our new method with a large suite of models, many of which from the automotive industry. The results show that almost all models can be oriented consistently and sensibly using our new algorithm.

Keywords: mesh repair, modelling, normal orientation, patch connectivity, visibility

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Bibtex

@INPROCEEDINGS{borodin-2004-consistent,
      author = {Borodin, Pavel and Zachmann, Gabriel and Klein, Reinhard},
       pages = {18--25},
       title = {Consistent Normal Orientation for Polygonal Meshes},
   booktitle = {Computer Graphics International 2004 (CGI 2004)},
        year = {2004},
       month = jun,
   publisher = {IEEE Computer Society},
    keywords = {mesh repair, modelling, normal orientation, patch connectivity, visibility},
    abstract = {In many areas of computer graphics, such as real-time rendering, mesh processing, etc., models are
                assumed to consist of correctly oriented polygons.  However, many geometric modelling tools (such as
                CAD systems), do not pay attention to the orientation of the normals when exporting polygonal
                models.
                
                In this paper, we propose a new method that can consistently orient all normals of any mesh (if at
                all possible), while ensuring that most polygons are seen with their front-faces from most
                viewpoints. Our algorithm combines the proximity-based with a new visibility-based approach. Thus,
                it virtually eliminates the problems of proximity-based approaches, while avoiding the limitations
                of solid-based approaches.
                
                Our new method builds a connectivity graph of the patches of the model, which encodes the
                "proximity" of neighboring patches. In addition, it augments this graph with two visibility
                coefficients for each patch. Based on this graph, a
                global consistent orientation of all patches is quickly found by a greedy optimization.
                
                We have tested our new method with a large suite of models, many of which from the automotive
                industry. The results show that almost all models can be oriented consistently and sensibly using
                our new algorithm.},
        issn = {1530-1052},
        isbn = {0-7695-2171-1},
  conference = {Computer Graphics International 2004 (CGI 2004)}
}