Geometric modelling in a three-dimensional environment

Computer animators have long had difficulties in defining and controlling the shape of deformable objects during motion. In the context of human figure animation, a new form of surface description has been developed, Murugaiyan & Clapworthy [1], which allows the surface to be manipulated by the adjustment of a single parameter. The form of the surface deformations produced by the operations is under the control of the user. The mathematical structures used are extensions of NURBS, but have a greater flexibility at the cost of marginally-increased overheads. The development of this tool enables the surface modelling of a deformable object to be speeded up considerably, and the paper describes a geometric modeller currently under construction which will use this facility to produce the desired object by ´virtual sculpting´, a process analogous to the production of real objects from clay. In this, the user is able to pull and push the surface shape to produce either rounded or sharp surface indentations or protrusions by direct interaction with the surface. The object is viewed stereoscopically and at present shutter glasses are used. These have the attendant problem of ghosting, but this can be removed by a subtract-from-background algorithm, Noble [2]. Ongoing work at De Montfort University [3, 4] will eventually allow enhancements using autostereoscopic displays and eye tracking. The object is oriented in three dimensions using a spaceball and the surface operations are controlled using a mouse. The reduction in the number of parameters employed in the surface description enables the operations on the surface to be performed by use of the mouse buttons. Thus, the shape of the object is defined by simple ´point and click´ operations providing an extremely rapid, interactive method of surface construction. It is anticipated that this modelling system could be used in a number of areas of work, including Virtual Reality. While the tool is still at the developmental stage, the paper lays out the complete conceptual basis for its construction and implementation