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_id	a081
authors	Greenberg S., Roseman M. and Webster, D.
year	1992
title	Issues and Experiences Designing and Implementing Two Group Drawing Tools
source	Readings in Groupware, 609-620
summary	Groupware designers are now developing multi-user equivalents of popular paint and draw applications. Their job is not an easy one. First, human factors issues peculiar to group interaction appear that, if ignored, seriously limit the usability of the group tool. Second, implementation is fraught with considerable hurdles. This paper describes the issues and experiences we have met and handled in the design of two systems supporting remote real time group interaction: GroupSketch, a multi-user sketchpad; and GroupDraw, an object-based multi-user draw package. On the human factors side, we summarize empirically-derived design principles that we believe are critical to building useful and usable collaborative drawing tools. On the implementation side, we describe our experiences with replicated versus centralized architectures, schemes for participant registration, multiple cursors, network requirements, and the structure of the drawing primitives.
series	other
last changed	2003/04/23 15:50

_id	aba4
authors	Lischinski, D. Tampieri, F. and Greenberg, D.P.
year	1992
title	Discontinuity Meshing for Accurate Radiosity
source	IEEE Computer Graphics & Applications, November 1992, pp.25-38
summary	We discuss the problem of accurately computing the illumination of a diffuse polyhedral environment due to an area light source. We show how umbra and penumbra boundaries and other illumination details correspond to discontinuities in the radiance function and its derivatives. The shape, location, and order of these discontinuities is determined by the geometry of the light sources and obstacles in the environment. We describe an object-space algorithm that accurately reproduces the radiance across a surface by constructing a discontinuity mesh that explicitly represents various discontinuities in the radiance function as boundaries between mesh elements. A piecewise quadratic interpolant is used to approximate the radiance function, preserving the discontinuities associated with the edges in the mesh. This algorithm can be used in the framework of a progressive refinement radiosity system to solve the diffuse global illumination problem. Results produced by the new method are compared with ones obtained using a standard radiosity system.
series	journal paper
last changed	2003/04/23 15:50

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