Israel SIGGRAPH meeting on June 13 1997

Chair: Dani Lischinski
Institute of Computer Science
The Hebrew University of Jerusalem

The following program is also available in PostScript format. The PostScript file is to be printed double-sided on A4 paper, and folded into three columns with INVITATION and the digit "5" on the exposed columns.

Time	Speaker	Title	Abstract
8:30		REFRESHMENTS
9:00	Yair Mann Tel-Aviv University	Selective Pixel Transmission for Navigating in Remote Virtual Environments	The speaker presented a technique to improve the performance of a walkthrough in remote virtual environments, where a scene is rendered jointly by the server and the client, in order to reduce the network requirements as much as possible. The client generates novel views by extrapolating a reference view based on the locally available geometric model, while the server transmits data necessary to prevent an accumulation of errors. Within this concept, the speaker showed that by transmitting only a selected subset of pixels, the quality of the extrapolated views can be improved while requiring less bandwidth. The talk focused on the selection process in which the visibility gaps between the reference view and novel view are detected, packed and transmitted compressed to the client.
9:30	Alain Fournier University of British Columbia	Representing Complex Objects with Unions of Spheres	Representing, simplifying, identifying and manipulating shapes has always been a challenge in computer graphics as well as in computer vision. The speaker presented and illustrated a representation of complex shapes consisting of a union of spheres (UoS) that can help towards meeting this challenge. The source data considered range from volumetric (CAT, MRI etc.) to the output of 3D scanners. The creation of the UoS from the data involves a Delaunay triangulation (tetrahedralisation in 3D) and the culling of redundant spheres. The simplification of the UoS involves the concept of sphericity (how well a group of spheres is approximated by a single sphere) and some heuristics. The speaker gave two examples of use of the UoS representation, one to establish a correspondence between two similar objects (for example to register two versions of the same objects), and another to interpolate between two dissimilar shapes (usually known as "morphing"). The speaker discussed the use of the UoS representation in defining a metric for shape differences, and issues such as the stability of the representation. Finally, he touched on practical issues such as the triangulation of the surface of the UoS, texture mapping and computation of mass properties.
10:30		COFFEE BREAK
11:15	Eric Andres University of Turku, Finland	Introduction to Arithmetical Geometry through a Medical Imaging Application	The speaker presented some basic notions of 2D arithmetical geometry through an application in medical imaging. He presented the 2D discrete line of Reveilles and a line recognition algorithm, and introduced the notion of discrete analytical representation form. These notions were illustrated in a pixel contouring and distance computation problem that occurs in cancer radiotherapy.
11:45	P. Kagan Technion - Israel Institute of Technology	A B-Spline Finite Element Approach for Designing Freeform Objects	In CAD systems, sculptured shapes are adequately represented by B-splines. For a pure geometrical approach, however, a large number of mathematical degrees of freedom is required to control the global behavior of a complex shape. Therefore, it is difficult to design sculptured and freeform surfaces with a CAD system that relies solely on a B-spline geometrical approach. To reduce this problem, the speaker proposed an alternative intuitive approach based on physical qualitative behavior, in which the model mechanism is based on a B-Spline Finite Element (FE) technique. The speaker discussed the influence of the inherent properties of B-spline FE on the physical-based model. These B-spline properties include uniform spacing (UBS) or non-uniform spacing (NUBS) of knot vectors and number and degree of the B-spline function. Several examples of sculptured surfaces designed using the proposed physically-based module were shown. Joint work with A. Fischer, P. Bar-Yosef and M. Shpitalni.
12:15	Y. Hochwald Technion - Israel Institute of Technology	Visualization of Meshes Based on Level of Detail Quadtrees	An advanced CAD method for visualization is required for efficient, real-time display of meshes derived from solutions such as the Finite Elements (FE) method. Such FE solutions are likely to contain a massive database. For real-time display, this data must be reduced while still preserving solution behavior. That is, even at lower levels of resolution, critical areas must be preserved. The speaker proposed an adaptive LOD technique for meshing. The meshes are represented by hierarchical structures, such as quadtrees. The LOD of the meshes describe changes in time and space for a physical and geometric surface at any level of resolution. This technique was demonstrated through colored 3D morphing between meshes at different times. In addition, an algorithm for isocurves based on the marching cube method was developed and implemented. Several examples of 3D morphing were demonstrated. Joint work with A. Fischer and P. Bar-Yosef.