3D Shape Representation

      My ongoing work in 3D shape representation has been inspired by the need to design more effective techniques for portraying the 3D spatial relationships between multiple overlapping or enclosing surfaces.
      Although transparency has the potential to be a useful device for conveying information about the relative positions and orientations of two or more superimposed layers  --   in an ideal transparent rendering, one would be able to view the multiple surfaces simultaneously and in their true context, and to rapidly intuit the complex 3D geometry of the scene  --   in practice, it is often difficult to adequately perceive the full 3D shape of a smooth transparent shell or to accurately judge its depth distance from underlying objects.
      Over the past years, I have investigated a variety of techniques for "artistically enhancing" transparent surfaces with sparse, opaque texture markings that intend to describe the essential character of the surface shape in a perceptually intuitive and minimally occluding way. The images below illustrate some of my more recent results.

  The slides from my talk at SIGGRAPH 97 provide a more complete, illustrated overview of this work.
click here for mpeg movie (rotation sequence)- 1.1M
click here for animated gif (rotation sequence)- 2.0M (or on image for mpeg movie- 1.1M)

This pair of images contrasts a traditionally rendered transparent surface with a rendering in which the transparent surface has been enhanced by a carefully constructed pattern of thin opaque lines. The intention of the lines is to both more explicitly define the 3D location of the outer surface (via more reliable occlusion and vergence cues), and to more clearly indicate its 3D shape. The texturing technique illustrated in the image on the right is described in my 1997 SIGGRAPH paper "Illustrating Surface Shape in Volume Data via Principal Direction-Driven 3D Line Integral Convolution" (2.4M pdf) (HTML).



This image shows an example of some slightly earlier work, in which I used the principal directions and principal curvatures at evenly distributed points over an isosurface to define the orientation and length of a polygonally-defined solid stroke texture.   This texturing technique and its perceptual motivation are described in   Interrante, Fuchs and Pizer. "Conveying the 3D Shape of Smoothly Curving Transparent Surfaces via Texture", IEEE Transactions on Visualization and Computer Grahics, 3(2):98-117 (3.3M pdf) (HTML).
 This reference also includes a description of the controlled observer experiments that we conducted to evaluate the potential effectiveness of the principal direction texturing approach.


click here for mpeg movie- 1.5M
click on the image above to see an mpeg rotation sequence- 1.5M

It's possible that principal direction stroke textures might have the potential to be useful for depicting the shapes of complex objects for other purposes, such as non-photorealistic rendering.   There are a number of obstacles that remain to be overcome before the techniques I've developed could be viably used for such purposes, however.   A foremost concern is the problem of satisfactorily removing the kinds of directional inconsistencies that are clearly visible across the broad upper areas on both sides of this image.   Other major concerns include developing a more appropriate stroke character, and improving the computational efficiency of both the principal direction estimations and the generation and application of the texture across the surface.



This image shows some of my earliest work in defining opaque texture markings for illustrating surface shape.   Inspired by the ability of artists to define a figure with just a few strokes, I sought to use the ridge and valley lines to define an orientation-invariant 3D "sketch" of the outer skin surface. The goal was to facilitate an immediate understanding of the 3D location of the relevant soft tissue structures indicated by the skin surface, without unduly obscuring the visibility of the underlying tumor and dose surfaces.   This research is described in the paper "Enhancing Transparent Skin Surfaces with Ridge and Valley Lines", proc. Visualization '95, pp. 52-59 (728k pdf).

Last updated: 11/17/97

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