An Empirical Study on Two-Handed/Collaborative Virtual Assembly

This paper describes an empirical study on object assembly in a virtual environment. The study evaluates the effectiveness and correlation of the following two manipulation supporting methods: “discrete placement constraints” and “collision avoidance” in both two-handed and collaborative virtual objects assembly. The results show that discrete placement constraints need practice to handle objects efficiently, while collision avoidance is efficient regardless of the user’s experience in both single user two-handed and two user collaborative virtual assembly. INTRODUCTION Virtual reality techniques can provide an intuitive user interface based on our spatial perception. If whole physical behavior of virtual objects were simulated perfectly, a user could manipulate virtual objects in the similar way as in the real world. Because of the limited power of current computers, however, it is difficult to calculate all of physical properties, such as gravity, collision and friction. Hence, certain practical methods for virtual object manipulation are required to make the interface feasible. So, a number of researchers have been attempting to develop fast algorithms for an accurate physical simulation[1, 2], or simple and effective algorithms for a comprehensible constraint on virtual objects movement based on their geometric or functional features[3, 4]. We have developed a virtual modeling environment, VLEGO, which employs two kinds of a manipulation supporting method: discrete placement constraints and collision avoidance. In VLEGO, owing to these methods, 3-D objects can be easily designed as with real toy blocks using two hands by assembling several primitives of boxand wedge-shapes[5]. We have conducted an empirical study on virtual object assembly to evaluate the effectiveness and correlation of these methods in both two-handed assembly by single user and collaborative assembly by two users. In the following sections assembling operation and two manipulation supporting methods used in VLEGO are first explained, and then the experiment is described. Figure 1: VLEGO display. ASSEMBLING OPERATION AND MANIPULATION METHODS IN VLEGO This section briefly explains an assembling operation and two manipulation supporting methods used in VLEGO. VLEGO has been developed to provide intuitive and quick ways for creating 3-D objects in a virtual environment. Figure 1 illustrates the workspace of VLEGO. VLEGO employs the metaphor of widespread toy blocks and has a few kind of boxand wedgeshaped primitives that are attachable to each other in the same way as real toy blocks. A user of VLEGO is able to perform assembly, decomposition, coloring and scaling of primitives to build 3-D objects. Assembling Operation The assembling operation in VLEGO utilizes two manipulation supporting methods described below, discrete placement constraints and collision avoidance, and plays the most important role to create 3-D objects in VLEGO. There are two types of assembly, onehanded assembly (picked object to non-picked) and cooperative assembly (picked to picked). Since we focus two-handed and collaborative assembly, only cooperative assembly is explained. Figure 2 shows cooperative assembly. When two picked objects are close enough to each other, the relative position and orientation of these objects are discretely aligned. If upper or lower faces of these objects contact each other after collision avoidance process, these are combined into a new object when one of these objects is released.