The AR Workbench: A Complete Co-located Reach-in Mirror-Based ...

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Marlon Richert, Master’s Thesis, Friday, 23 February, 2007 16 the desk, including a fork, a knife, and a spoon. Frank tells her that she can touch any of the pieces of virtual cutlery and it will automatically attach to the real handle she is holding. If she already has a piece of cutlery on the handle, it will at that point simply fall off and the new one will attach in its place. Frank suggests that she uses the virtual knife to cut a piece off the virtual apple. Carol touches the virtual knife with the real handle. She makes a slicing motion with the knife thru the virtual apple and a piece of the apple falls off. Franks then asks Gloria if she can use the virtual fork to move the virtual piece of apple to her mouth. Gloria does so and the piece disappears. They then continue to pretend to eat other items of virtual food. Table 5 Gloria calibrates the display (visionary scenario). Participating actors: Flow of events: Gloria: therapist 4.2 System Models Gloria has just recently moved her AR workbench to a new room and needs to recalibrate the display. She puts the video projectors in place and starts the calibration software. Each projector now projects a grid onto the projection screen. Gloria adjusts the projectors until their grids align. She then takes place behind the work and, while looking through the mirror, takes one of the motion trackers and places it in turn on the nearest two corners and the center of where she perceives the reflected projection to be. Each time she does so, she presses a key on her PC keyboard. The display is now calibrated and ready for use. This section details the models that describe the system. Figure 4 represents the functional model, which describes the functionality of the system from the user’s point of view. Figure 5 represents the analysis object model, which describes the structures of the system in term of concepts that are visible to the user. Figure 4 Functional model of the system (use case diagram).
Marlon Richert, Master’s Thesis, Friday, 23 February, 2007 Figure 5 Analysis object model of the system (class diagram). 4.3 Requirements Below are the elicited requirements of the system. These include functional and nonfunctional requirements. Firstly, the functional requirements detail the high-level functionality of the system. This includes the interactions between the user and the system. This list is quite short, the result of the desire to have a very generic system. Secondly, the nonfunctional describe constraints placed on aspects of the system that are visible to the user, as well as restrictions that the client (MedICLab) imposes on the system but that do not directly influence the user’s view of the system. 4.3.1 Functional Requirements The functional requirements are as follows: • The system shall be a complete, stand-alone AR workbench. • The system shall use mirror-based see-through AR. • The system shall be noninvasive to the user. • The system shall include a software library that enables the application programmer to set up interactions easily between virtual objects. • The system shall provide the application programmer with a high-level interface to the development environment, be it IPF or otherwise. • The system software shall reduce the time and knowledge of the development environment, be it IPF or otherwise, required to create highly interactive AR applications. • The system shall be able to provide the user with real-time, viewpointdependent stereoscopy. 4.3.2 Nonfunctional Requirements The nonfunctional requirements are as follows: • The system shall provide the user with a colocated reach-in AR interface. • The user shall be able to interact with virtual object using direct manipulation. • The system shall use one motion tracker to keep track of the user’s gaze and one motion tracker to keep track of the user’s action in the colocated space. • No prior knowledge or expertise with AR systems shall be required of the user to be able to use the system, but before starting a session, an expert will have to calibrate the system and register the user with it to ensure proper functioning. 17
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