User interfaces for three-dimensional geometric modelling

ABSTRACT

One of the biggest obstacles to the wider adoption of geometric modelling systems for three-dimensional objects is the relatively poor state of user interfaces. In geometric design, two forms of interface are required: one which permits rapid evaluation of the three-dimensional nature of an object and its relationship with other objects, and one which permits precise positioning and shaping of an object. Many systems provide one or the other but fail to provide both. The paper will address issues relating to both forms of interface, particularly in the context of current display technology. We first evaluate the pro's and con's of various attempts at true three-dimensional interaction before concentrating on the use of conventional displays for three-dimensional design. Issues of concern are speed of interaction, the precision and predictability of the interface, the information required to convey meaningful three-dimensional data, and the fidelity of the image to the stored geometric model. The paper discusses work in the Computational Geometry Project, University of East Anglia, aimed at improving user interfaces and in particular considers two systems for the design of mechanical objects. One implements a pseudo-English language for describing assemblies of three-dimensional primitives with the ability to describe and maintain constraints between these primitives in a natural way. The second system takes the user's isometric wire-frame sketch and attempts to generate, using user intervention where automatic means fail, a winged-edge data structure modelling the three-dimensional object. Both these systems rely to an extent on the concept of constraints and the paper concludes with the re-examination of the rôle of constraint based systems in computer-aided geometric design.

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INDEX TERMS

Primary Classification:
  H. Information Systems
  H.5 INFORMATION INTERFACES AND PRESENTATION (I.7)

Additional Classification:
  I. Computing Methodologies
  I.3 COMPUTER GRAPHICS
      I.3.6 Methodology and Techniques
          Subjects: Interaction techniques

General Terms:
Design, Human Factors, Management, Performance, Theory