RedirectedDoors is a visuo-haptic door-opening redirection technique in VR, and it has shown promise in its ability to efficiently compress the physical space required for a room-scale VR experience. However, its previous implementation has only supported laboratory experiments with a single door opening at a fixed location. To significantly expand this technique for room-scale VR, we have developed RedirectedDoors+, a robot-based system that permits consecutive door-opening redirection with haptics. Specifically, our system is mainly achieved with the use of three components: (1) door robots, a small number of wheeled robots equipped with a doorknob-like prop, (2) a robot-positioning algorithm that arbitrarily positions the door robots to provide the user with just-in-time haptic feedback during door opening, and (3) a user-steering algorithm that determines the redirection gain for every instance of door opening to keep the user away from the boundary of the play area. Results of simulated VR exploration in six virtual environments reveal our system's performance relative to user walking speed, paths, and number of door robots, from which we derive its usage guidelines. We then conduct a user study ($N=12$) in which participants experience a walkthrough application using the actual system. The results demonstrate that the system is able to provide haptic feedback while redirecting the user within a limited play area.

We propose RedirectedDoors, a novel space-efficient technique for redirection in VR focused on door-opening behavior. This technique manipulates the user’s walking direction by rotating the entire virtual environment (VE) at a certain angular ratio of the door being opened. This ratio is called door rotation gain. At the same time, the virtual door’s position is kept unmanipulated so that a realistic door-opening user experience can be ensured. We designed and implemented the rotational manipulation algorithm and two types of door-opening interfaces; with and without a doorknob-type passive haptic prop. We then conducted a user study (N = 12) to investigate redirection performance and user feedback as we examined three independent variables: door rotation gain, door-opening interface, and door-opening direction (push/pull). From the results, the estimated detection thresholds generally showed a higher space efficiency of redirection with our technique. Our results also showed that providing the haptic feedback led to a higher noticeability of redirection, but at the same time supported a higher subjective sense of realism and less discomfort. Following our results, we discuss which combinations of gain and door-opening direction can jointly provide lower noticeability and higher acceptability.