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Adaptive isocurve-based rendering for freeform surfaces
Elber G., Cohen E. ACM Transactions on Graphics (TOG)15 (3):249-263,1996.Type:Article
Date Reviewed: Dec 1 1996

The authors present an alternate method for rendering free-form surfaces. Traditional approaches triangulate the surfaces and use the resulting geometric data to compute rendering attributes. The actual pixel rendering is then performed with polygonal scan conversion, resulting in well-known artifacts and side effects due to consecutive approximations and polygon discontinuity. The authors propose a rendering method using direct evaluation and rendering of isocurves, the type of curves found in geological maps. In addition to already existing curve rendering algorithms, they offer to automatically extract from the surface an optimal set of isocurves to expedite rendering.

In the introduction, the authors review methods used for isocurve rendering, mentioning the drawbacks of the fixed-step approach and the one-time parameters initialization used in the curve/surface approximation. The authors’ approach reduces the redundancy in pixel covering that is generally present with other methods. Some rules are established to ensure that all surface pixels will be covered. Those rules take into account the maximum Euclidean distance between isocurves, to ensure surface covering, and the number of times a given pixel will be painted, to optimize rendering time.

An algorithm is proposed, unfortunately without much detail. It starts from the curved surface to be rendered and returns the set of isocurves satisfying the criteria mentioned above. The algorithm recursively constructs a set of isocurves, until each pixel of the surface is covered. The approach is fairly close to what several more traditional graphics packages already implement for rendering NURBS curves or surfaces.

The authors claim better highlighting and shading than in standard tessellation algorithms performing surface rendering. It would be interesting to compare the results obtained from the proposed implementation with those obtained when computing polygonal attributes in a specific coordinate system for lighting calculations.

This approach has numerous significant advantages: simplification of the trimmed NURBS surface approximation and rendering, simplification of their clipping, and better lighting and shading than when using standard tesselation into polygons. These advantages are attractive when implementing a fast, accurate rendering package. The authors mention little about rendering time. The number of calculations involved in curve and surface approximation is far from negligible; the authors claim comparable numbers when using their implementation and a regular adaptive method using the Alpha_1 solid modeler polygon-based renderer.

Reviewer:  Patrick-Gilles Maillot Review #: CR120338 (9612-1026)
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Color, Shading, Shadowing, And Texture (I.3.7 ... )
 
 
Curve, Surface, Solid, And Object Representations (I.3.5 ... )
 
 
Hidden Line/ Surface Removal (I.3.7 ... )
 
 
Splines (I.3.5 ... )
 
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