Computer Laboratory

Technical reports

Managing complex models for computer graphics

Jonathan Mark Sewell

April 1997, 206 pages

This technical report is based on a dissertation submitted March 1996 by the author for the degree of Doctor of Philosophy to the University of Cambridge, Queens’ College.

Abstract

Three-dimensional computer graphics is becoming more common as increasing computational power becomes more readily available. Although the images that can be produced are becoming more complex, users’ expectations continue to grow. This dissertation examines the changes in computer graphics software that will be needed to support continuing growth in complexity, and proposes techniques for tackling the problems that emerge.

Increasingly complex models will involve longer rendering times, higher memory requirements, longer data transfer periods and larger storage capacities. Furthermore, even greater demands will be placed on the constructors of such models. This dissertation aims to describe how to construct scalable systems which can be used to visualise models of any size without requiring dedicated hardware. This is achieved by controlling the quality of the results, and hence the costs incurred. In addition, the use of quality controls can become a tool to help users handle the large volume of information arising from complex models.

The underlying approach is to separate the model from the graphics application which uses it, so that the model exists independently. By doing this, an application is free to access only the data which is required at any given time. For the application to function in this manner, the data must be in an appropriate form. To achieve this, approximation hierarchies are defined as a suitable new model structure. These utilise multiple representations of both objects and groups of objects at all levels in the model.

In order to support such a structure, a novel method is proposed for rapidly constructing simplified representations of groups of complex objects. By calculating a few geometrical attributes, it is possible to generate replacement objects that preserve important aspects of the originals. Such objects, once placed into an approximation hierarchy, allow rapid loading and rendering of large portions of a model. Extensions to rendering algorithms are described that take advantage of this structure.

The use of multiple representations encompasses not only different quality levels, but also different storage formats and types of objects. It provides a framework within which such aspects are hidden from the user, facilitating the sharing and re-use of objects. A model manager is proposed as a means of encapsulating these mechanisms. This software gives, as far as possible, the illusion of direct access to the whole complex model, while at the same time making the best use of the limited resources available.

Full text

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BibTeX record

@TechReport{UCAM-CL-TR-420,
  author =	 {Sewell, Jonathan Mark},
  title = 	 {{Managing complex models for computer graphics}},
  year = 	 1997,
  month = 	 apr,
  url = 	 {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-420.pdf},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-420}
}