USING RECURSION TO DESCRIBE POLYGONAL SURFACES
Date
1984-04-01
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Abstract
We describe a three dimensional graphics system called PG (Polygon
Groper) and its use by artists for defining and viewing solid objects.
A simple set of commands in PG are used to manipulate 3D models. The
models are stored as a hierarchy of objects, where each object
represents a geometrical transformation of another object or a
primitive polygon. It has been found that a hierarchical structure
provides a more powerful way of building and manipulating 3D objects
than conventional linear structures. The object hierarchy also allows
recursion to be used to describe pictures which are difficult or
impossible to define in other graphics systems without considerable
programming effort. Although any recursive process may be expressed
iteratively, a certain class of pictures is more concisely defined
and more easily visualised recursively. Many tools are available to
aid the artist manufacture primitive objects. These tools generate the
surface polygons to describe different solids. PG offers a number of
alternative viewing algorithms. These provide the artist with successively
higher quality images at the cost of correspondingly greater time for
computation. PG is an integral part of the Graphicsland System, a
film animation system under development at the University of Calgary.
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Computer Science