Virtual sculpting enables the creation of computer models by emulating traditional sculpting. It can be implemented using spatial deformation, an interactive versatile modelling technique. Unfortunately, spatial deformation is limited to topology preserving warping. This is overcome by space-time objects, a variant of spatial deformation, which alters topology by extruding an object into 4-D, deforming the 4-D object and extracting a topologically altered object. However, they arc specifically targeted to animation. In this paper, we adapt space-time objects to interactive modelling by: employing a tetrahedral rather than parallelepiped representation; exploiting coherence during the constant projection into lour dimensions; and limiting projection to the portions of an object undergoing topology changes and thereby producing simpler triangulations of undeformed regions. Each of these adaptations is discussed in the context of the space-time object stages: extrusion, deformation and extraction. We also present preliminary results demonstrating the efficiency of our improvements.
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