# Comparative Evaluation of Different following Mechanisms in VR Guided Tour: A Preliminary Study
## 3 Material and Methods
### Following Mechanisms  
We first propose three types of following mechanisms, limited (L), semi-limited (SL), and not-limited (NL) (Figure 1). After a prior study, we add one more mechanism named improved semi-limited (ISL). We stated all as follows.  
* **Limited (L)**: Inspired by the pre-recorded 360 degree virtual tours, the virtual tour guide is always in front of the user at a fixed distance. This means the speed of the guide and the user are the same. The user can only rotate their head to change the orientation of the viewpoint; other movements, such as walking and teleporting, are not allowed in the environment.
* **Not limited (NL)**: Distance between the user and virtual tour guide is not limited. This means that the user can move anywhere to explore the world, even ignoring the tour guide. If the user wants to follow the tour guide, he/she has to move by using the controller manually.
* **Semi-limited (SL)** and **Improved semi-limited (ISL)**: There are two versions of the semi-limited mechanism. Both have the same concept: users can only move within a specific range around the virtual tour guide. The only difference is in the repositioning phase. In the original version, when the user moves out of the range (eight meters in the experiment), the user will be immediately transmitted to a new position behind the tour guide within the range without transition animation. To keep the user's spatial continuity, we hope the user's point of view is kept after the transition. Thus, after the transition, the new position is adjusted according to their heading direction such that the tour guide will always be in front of them. Hence, it is much easier for the user to find the guide. However, the prior experiment shows that the original version gives adverse experiences to most participants. They felt annoyed while experiencing the guided tour. Some of the users said they were dizzying. Furthermore, the result underperforms compared to the other two mechanisms. See Sections 4 and 5 for detailed experiment results.  
In order to improve the user experience, we adjusted the timing and the transition animation when the repositioning occurs. First, to reduce the frequency of repositioning, we set a ten-second interval between each reposition, which means even though if the user keeps walking away from the tourist guide, the repositioning will not be triggered consecutively, making users less annoyed. Second, we add some visual clues and animation to reduce the space discontinuity when repositioning users, as in Figure 2. The visual clues consist of a count-down timer telling users when the reposition will happen and an arrow pointing to the tour guide's position, similar to the off-screen enemy indicator in shooting games. For the transition animation, we add a gradual blur effect when the countdown starts. We also move users in a time-lapse mode instead of directly setting their new position. The progressive transition animation gives the user better spatial awareness.  
Figure 1: The different following mechanisms. **Left**: Limited. The user’s position is limited behind the guide (the cat in the figure). **Middle**: Semi-limited. The user is allowed to walk around the guide (in the blue circle) but will be automatically moved to the near-guide position if the user is far from the guide. **Right**: Not limited. The user can freely move anywhere in the virtual environment.