Development of an Augmented Reality system using ARToolKit

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Development of an Augmented Reality system using ARToolKit and user invisible markers 2.7 AR applications Now that has been presented all the building blocks needed for creating AR, the moment has arrived to take a closer look at application areas where AR has already been applied. There are several areas imaginable for AR, ranging from the most serious and demanding areas to the more entertaining and less requiring ones. In [Val98] , [Azu94] and [Azu97] are identified several areas; the aggregation of those results in the following list: • Medical • Military • Education • Engineering design • Manufacturing, maintenance and repair • Entertainment As stated in the introduction of this chapter, mostly HMDs are used for giving the user an augmented view on the real world. This also results from the carried out inventory of known AR applications. For the tracking subsystem usually optical tracking or a hybrid tracking approach is utilized. Tracking using GPS only is important for outdoor AR. The way interaction is implemented, completely depends on the posed application requirements. Surgeons would need an interaction mechanism comparable to the way medical instruments are used. But for soldiers in the battle field a non-obstructing manner of interaction is required. All this may result in different hardware setups for each mentioned area. Following are described AR systems that are taken from the six identified areas. These systems are either considered to be representative for their corresponding area, or are most innovative and generally known within the AR community. Hereby it is obviously unnecessary to note that this small selection can not give a full intersection of each area. 2.7.1 Medical In the medical area there can be distinguished four types of applications for AR; image guided surgery, surgery planning, surgical training and psychiatry. Here will shortly be discussed which possibilities exist for AR. For illustration, also in each category, a known AR system is presented. Thereby the focus will be on the before discussed topics; display technology, tracking, calibration, registration and interaction. 2.7.1.1. Image guided surgery Minimal invasive surgery and interventions promise advantages for the patient, such as reduced trauma, faster recovery and better cosmetic result. This comes at a cost of a restricted view of the region of intervention for the surgeon. Augmented reality can be used to minimise this or even overcome this lack of visual perception. Medical data can be overlaid on a patient for guiding a minimal invasive operation. Many medical areas lend themselves for this concept; brain, heart, liver, spine and knee surgery are just a small sample taken from the full range of possibilities. Some of those areas have more practical demands because of moving and deforming parts. 25
Development of an Augmented Reality system using ARToolKit and user invisible markers AR systems in image guided surgery roughly take the same approach. That is, first twodimensional data of the patient is acquired. These data are transformed into a threedimensional model. Secondly, there needs to be a way to register the real patient. Tracking of the patient, instruments and visualization displays also need to be taken care of. Finally, the created three-dimensional model is overlaid on the patient to provide the surgeon with an augmented view. Each AR system implements these steps in a different way. Now will be shortly discussed one such system, resulting from the MEDARPA project [Sch04]. The main component of the system is a transparent display attached to a movable swivel arm. The technology consists of a 17” TFT screen allowing a resolution of 1024x1024, at a resolution of 75Hz. A working area of about two square meters is supported. The transparent screen is used for overlaying acquired CT or any other 3D imaging modality on the body of the patient. The surgeon can interact with the patient in the normal way using medical instruments. To overcome the lack of stereoscopic view, colour coded feedback is used for guiding the surgeon. Tracking is supported by a hybrid tracking approach consisting of electromagnetic and optical tracking. The position and orientation of the patient, medical instruments, the display and the surgeon’s viewpoint are continuously tracked. For registering the patient a registering device is used based upon spherical markers which are attached to the patient’s body. Figures 2.33 through 2.35 show the system setup, its interaction mechanism and registration procedure. Figure 2.33 MEDARA Hardware Figure 2.34 Interaction Figure 2.35 Registration of the setup through a medical instrument patient 2.7.1.2. Surgery planning Not only offers AR possibilities for supporting the surgeon during an operation by image guided surgery, but it also can be used in the stages before an actual operation. This activity is known as surgery planning, which allows for predetermining optimal decisions, and thus for staging of operations. This relieves the surgeon during the operation, by not having to consider the next step or action to be carried out. As is the case with image guided surgery, AR for surgery planning, is also not limited to a small range of the medical area. It can be extended to any imaginable medical problem, given that it can be visualized in three dimensions. This is done through building up a 3D model from 2D CT, MR or ultrasound data. Now will be shortly discussed one such AR surgery planning system, taken from the area of livery surgery [Sor04]. 26
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