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With the advancement of computer techniques, a greater emphasis has been placed on intuitive human-computer interactions (HCIs). Virtual Reality systems can offer a novel way for users to interact with the objects in the computer generated environment (the so called Virtual Environment, VE). Through VR technology, we have the ability to replace the traditional input device, such as keyboard and mouse, with other modes such as speech and gesture. In our research project, we use a CyberGlove, developed by Virtual Technology Inc., as an input device to develop a desktop CAD modeling system for conceptual designers. We elaborate the limitations of the Dataglove and use gestures to support intuitive human-computer interface. To develop this gesture interface, we emphasize that conceptual designers are allowed full-freedom to use different kinds of gestures to conduct various geometric shape operations instead of depending solely on keyboard and 2D mouse. The designers can indicate objects or directions simply by pointing with the hand, and manipulate the position and orientation of an object by grasping and turning. The “virtual tools” can be used for shaping, cutting, and joining objects. We employ the 3D GUIs for enhancing the gesture interface. In the VE, the 3D menu and “virtual hand” float over the objects rather than being part of the scene. Various 3D cursors can be used to select menu or manipulate the object.

There is an increasing demand in the conceptual design for more intuitive methods for creating and modifying free-form curves and surfaces in CAD modeling systems. The methods should be based not only on the change of the mathematical parameters but also on the user’s specified constraints and shapes. This paper presents a new surface representation model for free-form surface deformation representation. The model is a combination of two functions: a displacement function and a function for representing an existing NURBS surface called parent surface. Based on the surface model, the authors develop two deformation methods which are named SingleDef (Single-point constraint based deformation method), and MultiDef (Multiple-points constraints based deformation method). The techniques for free-form surface deformation allow conceptual designer to modify a parent surface by directly applying point constraints to the parent surface. The deformation methods are implemented and taken in an experimental CAD system. The results show that the designer can easily and intuitively control the surface shape.

In this paper, methods for generating and flattening developable surfaces by means of two given directrix curves have been investigated. By finding the two end points of every generatrix, a developable surface may be formed. Such a developable surface may be flattened by rotating part of the surface about a generatrix. A new approach based on the principle of geodesic curve length preservation for flattening developable surfaces is also introduced. In this technique, an algorithm for evaluating the geodesic curvature of a point of a curve that lies on a surface is utilized.