The studies in this thesis mainly discussed on how to improve 3D multi- user interactive visualization with a shared large-scale display including display setups, interactive visualization, and visual fatigue. Although this thesis makes a number of important contributions it also has a number of limitations, which are discussed in more detail in this section.
Firstly, the study for the display setups for multiple users was conducted with loosely coupled collaborative tasks (collaborative tasks for each user were slightly related, which users could complete independently). Tightly coupled collaborative tasks (collaborative tasks that are strongly related so users need to do them together) may not be suitable for a split screen.
Secondly, the Object Shift Technique (OST) requires a larger virtual environment than the conventional Mean Tracking (MT) method. The OST shifts virtual objects in the opposite direction of the PoV movements, so it requires a virtual environment at least twice as large compared to its absent condition.
Thirdly, the Activity-based Weighted Mean Tracking (AWMT) method performs similarly to the MT method in the worst cases as mentioned in the
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worst scenario in section 4.2.2.2. In addition, the methods support 3D movements but only 2D movements (including left-right and back-forth) were evaluated during the experiment. The author assumed vertical movement (up-down) in the VE may be the same as 2D movements. However, it might be possible that scene change in vertical movement is more abrupt due to a sudden jumping action, which could influence the user experience and performance.
Fourthly, the author assumed that the experiment with a single user for the third study is similar to a 3D multi-user visualization with a single PoV due to the similar system configuration. However, the results might be different between the two configurations. A pilot test was conducted for the Adaptive IPD adjustment technique and the participants answered that interactive visualization with adaptive IPD Adjustment was better than 3D stereoscopic visualization with fixed IPD. However, it might be possible that the results may differ with multiple users compared to the single user configuration tested in the experiment.
Fifthly, the framework requires manual process in setting up displays to build a VR system. The framework provides the display setup configurator to simplify building of the VR system. However, it still required manual work to set up the display because the framework cannot know how physical environment is set.
Sixthly, the author found that the framerate differs between the framework and devices, which might cause potential problems by missing packets. When the framerate of the framework is slower than devices, the framework can accumulate the command packets, and occasionally misses the command packets. The framework tries not to ignore the command packets as much as possible. However, packet loss can still occur, which may require users to perform input action again. Though this problem was partially solved by
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matching the framerate between the framework and the control devices, and other processes, it may not be solved perfectly because the framerate cannot be matched exactly.
Lastly, the prototype VR system was rigorously assessed with user study. The system was built to support the multi-dimensional objectives decision making. Due to the various types of data to visualize, the author had to mix 2D and 3D visual objects together in the same environment, which might cause visual fatigue. The author conducted a pilot study with a small number of users. The participants answered that they did not feel severe fatigue from the mixed virtual objects because the display screens are separated and big enough to focus on a single screen. However, it might require further investigation on if the mixture of 2D and 3D visualization would cause visual fatigue.
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Conclusion
This chapter concludes the dissertation. The author summarizes the presented work and describes directions for future research. The main goal of this Ph.D. was to improve 3D multi-user interactive visualization with a shared large-scale display. The main contributions of this thesis are listed below:
1. A literature review of multi-user interaction with a shared large-scale display and relevant areas. The review focused on display setups, interactive visualization, and 3D visual fatigue for multiple users. (Chapter 2)
2. Deeper insights into three display setups for multi-user interaction with a shared large-scale display. (Chapter 3)
3. Development of two novel multi-user interactive visualization techniques (the Object Shift Techniques and the Activity-based Weighted Mean Tracking method) that support interaction with multiple users and help to reduce the visual fatigue. (Chapter 4) 4. Development of an Adaptive Interpupillary Distance Adjustment
technique that can reduce visual fatigue caused by the extreme disparity between the views of the users’ left and right eyes. (Chapter 5)
5. Demonstration and user evaluation of three display setups (a shared view, a split screen, and a split screen with navigation information). The user study includes the evaluation of interaction performance, collaborative usability, and user preference. (Chapter 3)
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6. Implementation and evaluation of the three novel interaction techniques (the Object Shift Techniques, the Activity-based Weighted Mean Tracking method, and the Adaptive Interpupillary Distance Adjustment technique). Each user study measured interaction performance, depth perception, visual fatigue, usability, and performance. (Chapter 4 and Chapter 5)
7. Development of a framework for supporting a multi-user interaction with a shared large-scale display and its application to multi- dimensional decision making VR system. The framework not only supports the novel interaction techniques mentioned above but also includes fundamental multi-user interaction functions such as head tracking, network synchronization, and 3D visualization. (Chapter 6) The main results of each study and the development are summarized in section 8.1 and potential future works are introduced in section 8.2.