# Exploring the Effect of Virtual Environments on Passive
## 4 Implementation  
In this section, we describe our implementation method concerning transformation parameters and the experimental setup for passive haptic perception. Figure 4 shows our system configuration used to evaluate passive haptic perception. We compared the transformation difference in terms of participants' sense of passive haptic interaction. In our implementation, the participant in a virtual environment wore the HMD, and an optical-based tracking device called Optitrack Trio was installed for hand interaction [21]. Marker sets for hand tracking only visible in the optical camera were attached to the back of the hand. To set up our experiment, we adopted the method used by [PERSON] et al., who investigated the effects of the participant's perception on an augmented reality (AR) experience [3]. We used a real cubic puzzle (or cube) to provide passive haptic cues and applied a transformation comparison in our experiment. The participant was seated on a chair in front of a desk. Then, the subject was allowed to experience the same virtual space in the HMD as the real one. For instance, the participant could interact with the virtual cube on the desk in the virtual environment, and they compared the different types of transformation conditions in relation to passive haptic perception between the real cube and the virtual one. For the initial setup to match the virtual and real space, we applied scale calibration by measuring the size of the real environment (e.g., the desk's horizontal and vertical dimensions) using optical reference marker sets. Because we focused on the effect on the setting parameters, manipulation of the virtual object was not applied. Figure 4 shows an example of different position factors in our system configuration of passive haptic perception. In the case of the position factor for passive haptic perception, we investigated how participants perceived the position of the virtual cube in slightly different conditions. Figure 3: Our process to evaluate the effect of passive haptic perception in immersive virtual environments using three types of transformation conditions. As outlined in Table 2, the test conditions in our system for passive haptic perception consisted of five steps for each transformation factor (e.g., the distance for the position factor was scaled in five steps from \(-30\) cm to \(30\) cm). Figure 5 shows an example of different position factors by adjusting five steps along the \(z\)-axis, including the exact position of the real and virtual objects. According to prior simple experiments as already mentioned, there were many cases in which participants could not find the passive haptic prop to touch; thus, we only set the position to change along the error-free \(z\)-axis. Then, the participant was able to compare the position of the virtual cube with the actual one. Figure 6 shows an example of passive haptic interaction with different scale parameters. In our implementation for scale perception, other parameters such as position and orientation were maintained in their same conditions. For test conditions, we used Unity3D to visualize a 3D virtual cube to represent the same shape and material as the real one, and the virtual hand was allowed to move as a rigid body without finger movement [22]. To visualize a virtual hand with resemblance to an actual person, we dynamically interpolated the position of the virtual hand during a reaching motion as a function of the distance of tracked physical reaching to calculate hand motion [4]. Moreover, when a collision situation between a virtual hand and a virtual cube was recognized in a specific area with a threshold value, the motion animation of the virtual hand holding the cube was automatically generated. In test conditions for immersive 3D displays, the subject wore a head-mounted display (Oculus Rift [23]) to view and interact with the virtual cube. We used a real cubic puzzle with a size of 5.5 cm.