Evaluation of Published Algorithms
for Terrain Silhouette Rendering
at Interactive Rates
© Mahes Visvalingam and co-authors, 2002

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Evaluations of:

  1. Everitt's One Pass Silhouette rendering with Cube Maps
  2. Raskar and Cohen's Two Pass Algorithms

Abstract

Much of the literature on Silhouette Rendering tends to report on the author's proposals.  This is often sufficient for many applications of Non-photorealistic Animation and Rendering (NPAR), such as art.  However, verification is a critical part of scientific activity.  This series of investigations were to identify the best algorithms for artistic rendering of terrain data for scientific applications (see Visvalingam, 1999). 

This page provides a brief summary of some evaluations of a few algorithms for rendering silhouettes at rates suitable for interactive visualisation of terrain models as large as 500 x 500 x 2 triangles which are commonly used in scientific and environmental applications.  The investigations are on-going and are by no means exhaustive in their coverage of methods.  It is important to bear in mind that all evaluations assess fitness for set purposes. Hence our conclusions may not be relevant to others.  Also, authors are continually improving on their ideas and methods; so readers are referred to their websites whenever possible.  

1.  Everitt's One Pass Silhouette rendering with Cube Maps

This investigation was undertaken by Ruzi Che Mat as a part of his 4-month Dissertation project in part fulfilment for an MSc in Computer Graphics and Virtual Environments at the University of Hull.  The project was supervised by Mahes Visvalingam.

The approach

Graphics card : nVidia GeForce MX2
Software : cubemap_toon, at  http://developer.nvidia.com/view.asp?IO=1Pass_Silhouette_Rendering
Paper : Cass Everitt (2000) One Pass Silhouette Rendering with GeForce and GeForce2. http://developer.nvidia.com/docs/IO/1246/ATT/silhouette_demo.doc
Status : more recent algorithms on web.  Check out http://developer.nvidia.com/view.asp?IO=silhouette_rendering

Evaluation
For an abstract of Ruzi's thesis (Che Mat, 2001)- abbreviated version at: http://staf.uum.edu.my/ruzinoor/dissertation.htm
A brief illustrated report on this evaluation is provided by Ruzi Che Mat and Mahes Visvalingam

Conclusion
Reject :  As it stands, this one pass algorithm does not provide appropriate silhouettes for scientific visualisation of terrain.
However, it can provide acceptable impressionist sketches of other types of data, e.g. those used in games development.

Acknowledgements

Our thanks to: Cass Everitt of nVidia for checking our evaluations and for his comments on this evaluation;
The Ordnance of Great Britain for permission to use their sample data set in our research programme;
Chris Mathers for his Visual C++ program to read and render dem data at the start of Ruzi's project.
John Whelan and James Ward for pointers to the cubemap_demo

2.   Raskar and Cohen's Two Pass Algorithms

This investigation was undertaken by Ruzi Che Mat as a part of his 4-month Dissertation project in part fulfilment for an MSc in Computer Graphics and Virtual Environments at the University of Hull.  The project was co-supervised by Mahes Visvalingam and James Ward, who undertook further investigations.

The approach

Graphics card : nVidia GeForce MX2 [CHECK]
Software : Sil2 demo available from same address as paper.
Paper : Raskar R., Cohen M., 1999, "Image Precision Silhouette Edges". In Spencer S. N., editor,
Proceedings of the Conference on the 1999 Symposium on interactive 3D Graphics,
New York, April 1999. ACM Press., pp. 135 - 140.  Available online: http://www.cs.unc.edu/~raskar/NPR/sil.html
Status : More recent algorithms on web.  Check out http://www.cs.unc.edu/~raskar/HWWS/

Evaluation
For an abstract of Ruzi's thesis, please see his web page at: http://staf.uum.edu.my/ruzinoor/dissertation.htm
A brief illustrated report on this evaluation is provided by Ruzi Che Mat, James Ward and Mahes Visvalingam

Evaluation
The suitability of the following variants of the two pass algorithm were evaluated through the Sil2 demo program:

  1. Wireframe Method
  2. Z-scaled Translation
  3. Fattened Polygons
  4. Charcoal Effect

Conclusion
Adopt:  The Wireframe Method could be useful for real time rendering of silhouettes of terrain even if is not ideal for static frames or printed maps.
Reject : Both the methods of z-scaling by using different depth ranges and polygon fattening were less useful for scientific visualisation of terrain. 

Acknowledgements

Our thanks to: The Ordnance of Great Britain for permission to use their sample data set in our research programme
Page maintained by: Mahes Visvalingam
Last updated on July 2002

Cartographic Information Systems Research Group, University of Hull