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Researches on Model of Navigation in CVE 3.2 Navigation model Since the above features show that individual navigation can not apply in collaborative virtual environment, navigation model need to be developped. we are interested in the behavior of referring in conversation, since many of the difficulties in collaborative navigation are related to the problem of understanding what others are referring to[6].In this area, Clark’s[7] model of referring communication is representative. In his model, referring is a recursive process of seeking mutual acceptance between conversation partners. In CVE, however, a pure verbal conversational model is not sufficient; since participants could use graphically represented action instead of utterances to communicate. These actions often serve as an indication or verification of the referent. A user may manipulate her avatar to face towards the referred object, or highlight the object using a light ray. Based on previous research, we develop collaborative navigation model (Figure 3).The gray area is a spatial goal stack, which holds the user’s task goal and the sub-goals. The dashed-line loop within the big rectangle is an evaluation process for handling incoming inputs from the visual or verbal channel, and for deciding which operation will be taken on the goal stack.. Verbal and visual scan input could trigger the evaluation process. Some new goals may be pushed in, or some goals be popped out because of its evaluation being complete, or too difficult to accomplish. The solid arrow lines starting from spatial goal and back to cognitive map constitute the visual searching and tracking loop(Figure 4).  Figure3. Collaborative navigation model.  Figure4. Individual navigation process. The collaborative part comes in when two individual navigation processes interact. The current state of technology supports two types of interaction between geographically distributed individuals: verbal communication and correlated views. When it is a serial process and time-consuming, people naturally turn to the visual channel, and try to make views across different sites correlated so that information can be transferred. We believe what is needed for a successful collaboration is not the shared view, but the shared mental model of what being worked on. Because of the currently limited channels (visual, verbal) available to convey information across distance, we have to better design the information presentation in these channels, so that the collaborative partners can correctly infer a shared model of the work environment. To do so, we need to examine the bigger loop across the site boundary (Figure 5):  Figure5. Interaction loop process. The goal is to make the individual cognitive map gained during these big loops compatible with each other. Here, we are interested in finding the proper correlated views that ease the inference of a shared cognitive map. Views in different sites can be correlated in many ways, such as perspectives, LODs, scales and so on. Given a task, we want to study what are the good ways to correlate views in different sites, such that more useful information for constructing shared mental models is transferred. 4.Conclusion We have developed a simple collaborative virtual environment system. Based on our process model of collaborative navigation, we make some hypotheses regarding the effects of varying perspectives on collaborative navigation performance for the system. By our experiment, the hypotheses have been proved to be right. Although it is a work in progress, we have shown that our process model could make some predictions about the collaborative navigation performance under different display conditions. The research problem of how different perspectives affect collaborative navigation, many interesting issues still remain for further investigation. Then we can study concerning collaboration and spatial awareness on the basis of the model farther, which takes inportant role in theory. 5.References
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