DETERMINACIÓN DE LA CAPACIDAD DE ACOGIDA DEL TERRITORIO

In this technique, users make body gestures similar to the real world walking, without actually moving in the actual area. This way, users can walk virtually and explore a larger virtual world. Important advantages of the walking in place technique can be listed as cost effectiveness [20], naturalness, stronger feeling of presence and being easy to learn as compared to other approaches [69], and proprioceptive feedback similar to real walking [70].

One of the first scientific implementations of the walking in place technique was published in 1995 [71], [69]. In the implementation, the head movements were analyzed while performing walk-in-place gesture, and the virtual walking was triggered by the movement of the head. The latencies were large; the system required four steps in place to start the virtual walking, since false-positive steps (moving viewpoint when the user

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was not walking in place) were considered more confusing than a late start. Similarly, the system looked for no steps for two cycles to stop the virtual walking.

Since then, different aspects of the walking in place technique have been examined, such as step detections, start and stop latency [20]; and smooth speed control [72]. Smooth speed control was important because of the phenomenon of visual cues making the users feel like they are running with a slower speed than the actual treadmill speed [73], [74]. A detailed study showed that the recommended range for the visual gain was between 1.65 and 2.44 for the walking in place technique [75]. The same study showed that the gain values varied across different field of views; gain values increasing as the field of view decreasing.

One of the lowest latency walking in place technique was proposed by Feasel et al. [20]. In their study, they used a series of filters and numeric differentiations to obtain heel speed, and then they calculated the virtual locomotion speed after some signal processing operations. Their technique not only had low latency for both start and stop, but also had smooth movement, speed control during stepping and high turning responsiveness. They used magnetic sensors on the feet and the knees for tracking, but the same technique could work with more common optical motion tracking systems as well. A similar study was performed by Wendt et al. [76]. The proposed system used a biomechanical state machine to control the virtual walking, and found more consistent output speeds as compared to the study of Feasel et al. A similar recent study used two smart phones that were attached to the ankles of the user to track leg movement using the inertial sensors that were built into the phones. It triggered the walking in place

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technique after analyzing the acceleration data collected by the smart phones in real time [77].

Usually, the walking in place gesture looks like alternately pulling one’s knees up, similar to soldiers marching in place. A recent study proposed two different gestures as alternatives to the original walking in place gesture [78]. The first one was called the “Wiping Gesture” in which the user alternately bended each leg backwards whereas kept the upper leg almost still, instead of pulling the knees up as in the original walk-in-place gesture. The second one was called the “Tapping Gesture”, where individuals alternately lifted their heels without lifting their toes. The study showed that the Tapping Gesture was perceived as the most natural gesture as compared to the other two gestures. Furthermore, the perceived required physical effort for the Tapping Gesture was closer to real walking. In another study, some of the same authors examined two more input gestures; hip movement and arm swinging [79]. The user study results showed that arm swinging was perceived by the users as natural as the original walk-in-place technique, in terms of the perceived energy required, arm swinging was perceived as closest to real walking.

Different tracking techniques have been proposed for the locomotion techniques in this category. Some applications used knee positions to detect the walking in place gesture [80], and some techniques tracked shins for lower latency [20], [76]. Other techniques tracked the contact points of the feet with the ground. One study used an inexpensive commercial product, the Nintendo Wii Fit Balance Board, for this purpose [81]. They could successfully detect the walking gesture and found similar results in

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turning errors and mean latency, as compared to real walking. Another study used a camera under the ground plane of a six-sided CAVE-like projection system for processing the feet shadows when they were in contact with the ground [82]. The technique was called “Shadow Walking,” and could identify different feet gestures to be used for a broader range of movements, such as sidesteps. Shadow Walking was easy to install and suggested as an inexpensive solution to detect walking in place in six-sided CAVE systems. It also did not require an attachment on the body of the user.

For applications that require walking in three-sided CAVE-like systems, the user is likely to walk into the missing fourth wall. For this purpose, a technique called “Redirected Walking in Place” [83] combines the previously discussed redirected walking and walking in place techniques to reduce the frequency with which the user sees the missing wall. In a study, this technique did not lower the mean value of the fraction of time the users saw the missing wall, but it reduced the variance value.

Lastly, Terziman et al. studied a variation of the walking in place technique which required explicit head gestures [84]. For different actions, different head gestures were defined and a simple web camera checked these gestures in real time. These gestures were; lateral head motion for walking, head roll motion for turning, and vertical head motion for jumping and crawling. This technique worked in both sitting and standing configurations. While easy to implement and inexpensive, head gestures for walking was unintuitive and required training and practice before comfortable use.

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