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- Sherif Ghali, A. James Stewart
- Symposium on Computational Geometry
- 1996

Consider a viewpoint moving amongst a set of non– intersecting line segments in the plane. We would like to compute efficiently the set of segments visible at successive positions along the viewpoint trajectory. This problem can be solved in either the off–line or the on–line setting. The latter case, in which the updates of the viewpoint are known only as… (More)

- A. James Stewart, Sherif Ghali
- CCCG
- 1993

Given a set of polyhedra and a polygon in E3, the –aspect graph is a partition of the faces of the polyhedra into regions such that the area of that is visible from each region has the same structure or “aspect.” We present an output-sensitive algorithm to compute the –aspect graph. In computer graphics, this problem arises in rendering images of polyhedral… (More)

- A. James Stewart, Sherif Ghali
- SIGGRAPH
- 1994

This paper describes a fast, practical algorithm to compute the shadow boundaries in a polyhedral scene illuminated by a polygonal light source. The shadow boundaries divide the faces of the scene into regions such that the structure or “aspect” of the visible area of the light source is constant within each region. The paper also describes a… (More)

Consider the following problem: A viewpoint moves amongst a set of line segments in the plane and it is desired to maintain the sequence of lines visible from the viewpoint at every increment in its position. The sequence of visible lines is identical for most increments in the position of the viewpoint. It is diierent only when the viewpoint crosses a… (More)

- Todd Keeler, John Fedorkiw, Sherif Ghali
- Computer-Aided Design
- 2007

We introduce a novel representation for visibility in three dimensions and describe an efficient algorithm to construct it. The data structure is a spherical map that consists of a doubly–connected edge list embedded on the surface of a sphere. Each face of the spherical map is labeled with the polygon visible in the corresponding cone. We demonstrate that… (More)

- Sherif Ghali, A. James Stewart
- Graphics Interface
- 1996

This paper presents a treatment of first–order discontinuities (D1) that arise in discontinuitymeshes. An algorithm is described that, given a planar D1 discontinuity surface in a polyhedral scene, computes the corresponding discontinuity curves on the faces of the scene. A method is described to efficiently update the backprojection across a D1… (More)

- Sherif Ghali
- 1998

We consider visibility and shadow problems in the plane under static and dynamic conditions. We show that several problems in this domain are intimately related and that a careful formulation of the requirements of each problem can lead to a great deal of reuse in the implementation. This is of interest to the practitioner who may find it difficult to… (More)

- Sherif Ghali
- The Visual Computer
- 2008

Computer graphics is ostensibly based on projective geometry. The graphics pipeline—the sequence of functions applied to 3D geometric primitives to determine a 2D image—is described in the graphics literature as taking the primitives from Euclidean to projective space, and then back to Euclidean space. This is a weak foundation for computer graphics. An… (More)

- Sherif Ghali
- 2001

- Sherif Ghali, Christopher Smith
- CCCG
- 2005

We describe an algorithm that computes the boundary of the shadow volume cast by a collection of piecewise linear polyhedra in space using BSP trees. Unlike boundary representations, representing solids in general and shadow volumes in particular using BSP trees makes it possible to implement boolean operations easily and robustly. Also, in contrast with… (More)