Browsing by Author "Wyvill, Geoff"

Now showing 1 - 6 of 6
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    ANALYSIS OF AN ALGORITHM FOR FAST RAY TRACING USING UNIFORM SPACE SUBDIVISION
    (1987-10-01) Cleary, John G.; Wyvill, Geoff
    Ray tracing is becoming popular as the best method of rendering high quality images from three dimensional models. Unfortunately, the computational cost is high. Recently, a number of authors have reported on ways to speed up this process by means of space subdivision which is used to minimize the number of intersection calculations. We describe such an algorithm together with an analysis of the factors which affect its performance. The critical operation of skipping an empty space subdivision can be done very quickly, using only integer addition and comparison. A theoretical analysis of the algorithm is developed. It shows how the space and time requirements vary with the number of objects in the scene.
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    FIELD FUNCTIONS FOR IMPLICIT SURFACES
    (1988-01-01) Wyvill, Brian; Wyvill, Geoff
    The use of 3D computer generated models is a rapidly growing part of the animation industry. But the established modelling techniques, using polygons or parametric patches, are not the best to define characters which can change their shape as they move. A newer method, using iso-surfaces in a scalar field, enables us to create models that can make the dynamic shape changes seen in hand animation. We call such models Soft Objects. From the user's point of view, a soft object is built from primitive key objects that blend to form a compound shape. In this paper, we examine some of the problems of choosing suitable keys and introduce some new field functions that increase the range of shapes available as keys.
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    RAY TRACING IN CALGARY AND OTAGO
    (1987-03-01) Wyvill, Geoff; Wyvill, Brian; Cleary, John
    No abstract
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    SOFT OBJECTS
    (1985-10-01) Wyvill, Geoff; McPheeters, Craig; Wyvill, Brian
    We introduce the concept of soft objects whose shape changes in response to their surroundings. Established geometric modelling techniques exist to handle most engineering components, including free form shapes such as car bodies and telephones. More recently, there has been a lot of interest in modelling natural phenomenon such as smoke, clouds, mountains and coastlines where the shapes are described stochastically, or as fractals. None of these techniques lends itself to the description of soft objects. This class of objects includes fabrics, cushions, living forms, mud and water. In this paper, we describe a method of modelling such objects and discuss its uses in animation. Our method is to represent a soft object, or collecion of objects, as a surface of constant value in a scalar field over three dimensions. The main technical problem is to avoid calculating the field value at too many points. We do this with a combination of data structures at some cost in internal memory usage.
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    SOLID TEXTURING OF SOFT OBJECTS
    (1987-01-01) Wyvill, Geoff; Wyvill, Brian; Pearce, Andrew; McPheeters, Craig
    Since the shape of a Soft object changes in response to its surroundings, it is difficult to give a single position in space as the location of the object. Indeed objects can and do break into sub-objects dynamically. This means that you cannot map a solid texture onto such an object simply using a function of the space co-ordinates. We have taken a different approach. Our soft objects are modelled as the volume enclosed by an iso-surface of a field calculated from a set of key points. We ascribe to each key point a set of values which represent a position in an abstract texture space. Any point on the surface of an object has a field value due to each key point and this value is used as a weight in finding a weighted vector sum of these positions. This vector sum is used to select a surface specification from the texture space. These textures retain their consistency during distortion and metamorphoses of objects. A great variety of animation effects can be achieved with this process.
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    USING SOFT OBJECTS IN COMPUTER GENERATED CHARACTER ANIMATION
    (1987-01-01) Wyvill, Brian; Wyvill, Geoff
    The animation of 3D computer generated models is a rapidly growing part of the animation industry. One of the major criticisms that traditional animators have of this art form is the apparent inability to generate characters that can make the dynamic shape changes seen in hand animation. Recent work with SOFT objects, which change shape as they move, has proved to be a promising method for producing such characters. Specifying such changes is a complicated task which has received little attention in the literature largely because it is difficult to represent such objects using existing techniques. The SOFT objects presented here are represented by a surface constructed around a set of key-points and lines. This paper summarises previous work on SOFT objects and introduces some new field functions for their representation. Some methods are presented for describing the animation of SOFT objects, by determining the motion of the key points using both mathematical descriptions and physical simulations.