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Researches on Model of Navigation in CVE Zhang Jing, Liu Jianzhong, Wan Gang, Guo Yanbin Institute of Surveying and Mapping, Information Engineering University, Zhengzhou 450052, China Email: gybzj@163.com 1. Introduction The prospect of collaboration among geographically dispersed participants over a networked virtual reality is quite attractive. CVE involve the use of distributed VR technology to support group work. A necessary, but not sufficient, condition for a CVE is the provision of simultaneous multi-user access to a virtual reality system. However, there may be a world of difference between a multi-user system and one that actually supports cooperative work, and so a second condition is that the system must explicitly consider and support the needs of users who wish to work together. The essence of CVE is that users are explicitly represented to each other within a shared space[1]. Furthermore, they should be free to move around within this space, encountering each other and also objects and information of common interest. The interactive nature of true virtual reality systems means that they should also be able to interact with each other and with the objects and information. The development of effective CVEs has greatly increased the scope of CSCW, and it is now foreseeable that in the near future there will be experts separated by great distances, who will be working on problems together within a Virtual Environment (VE). CVE supports independent viewpoints for its users. Users themselves are represented to others through some types of embodiments, such as a screen name, a cartoon figure or a picture. In CVEs that are rendered in 3D graphics, users have graphical embodiments that are usually called avatars. In a typical CVE, there will be many avatars that populate the virtual environment. Each avatar represents and is controlled by one of the users. As a promising technology, Collaborative Virtual Environment (CVE) has already had many experimental applications in the fields of geo-data visualization, collaborative design and scientific exploration which are currently the domain of single user virtual reality applications may also offer possibilities for collaboration. Many of these applications have the element of collaborative navigation, in which several users explore the environment independently and then try to work together on some interesting points in the environment. 2. Individual Navigation in CVE It is not a trivial task for users to coordinate among themselves and to achieve their navigational goal in an virtual environment. Spence[2], Wickens[3] and Bakker[4]proposed some general frameworks for navigation processes. Spences’ model spans a whole range of navigation tasks including those in physical, virtual and information spaces. In fact, his definition of navigation is “the creation and interpretation of an internal mental model”(Figure 1).  Figure 1. A general framework for navigation The framework consists of four stages: Browse stage. The navigator perceptually registers the environmental content around him. The environmental content is the information that can be elicited from the navigation space. Modeling stage. The registered environmental content is used to build an internal mental model of the environment on both the local scale and a more global scale, providing understanding of what is perceptually available as well as how it fits into the larger picture. Interpretation stage. The internal mental model is used to decide whether the goal has been reached or whether the browsing strategy should be revised. Formulate browsing strategy stage. The browsing strategy is revised and a new direction for movement is chosen. Though Spences’ model is simple,it involes the components of Model(cognitive map), strategy, search (browse) and consist of recursive loops which are necessary for collaborative navigation. Figure2 shows Bakkers’navigation framework. The framework describes the mental processes and the information flows. The operator needs to have some internal representation of his own current location, both the position and the orientation, in order to determine a route or a direction of movement. Recognition, path integration and cognitive anticipation operate to determine the internal representation of the current location in the world. The model is applicable to immersive VE. Our collaborative navigation model is from many reference to the individual models.  Figure 2. Bakkers’ navigation model. 3. Collaborative Navigation 3.1 Features of Collaborative Navigation The previous work deals mostly with the problem of individual navigation. Since navigation performed by groups has its own characteristics that go beyond individual navigation, we focus on the collaborative aspects of navigation in CVE. In the task of a scientific collaboratory, each of the scientists moves about the space and thus controls her viewpoint independently, and tries to find scientifically interesting points in the data space.They need to know their spatial surroundings, and coordinate themselves to accomplish their goal, which is often achieved through navigation in the space. This type of cooperative spatial navigation activity is named collaborative navigation[5]. I would like to list some characteristics.
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