# Experimental Analysis of the Behavior of Mirror-like Objects in LiDAR-Based Robot Navigation
## 5 Experimental Results
### Data Collection  
* Case 1: One frontal mirror (Figure 7a)  
At position A, the top borders of the environment have not yet been formed (Figure 8A). This is due to the LiDAR range, which is approximately 10-11 feet. When the Turtlebot moved toward a plane mirror, the mirror was not detected, and some boundary reflections were observed. Being within the detection range of LiDAR, the Turtlebot detects itself when it moves perpendicular to the mirror due to the specular reflection property of the mirror (Figure 2). At position B, the upper boundary is now in range, and the entire experimental area should be mapped. However, the mirror location is still not detected, and the area within the field of view between the mirror location tapered to the LiDAR is still unaccounted for, showing up as an unmapped area in the RViz visualization tool (Figure 8B). At position C, the robot has completed its course. As the mirror is a plane mirror, the reflections of some parts of the boundaries are equidistant from the surface of the mirror as the physical boundary (Figure 8C). This situation is associated with the light transmission property (Figure 2). In other words, the LiDAR system wrongly recognized the reflective surface with a transparent surface. Another interesting observation is that the Turtlebot itself was detected on the surface of the mirror when the robot was in the normal range to the mirror. However, some parts of the mirror remained undetected. Figure 6: Constructed experimental setup and representation of the various mirror position condition setups with mobile robot locations A, B and C.  
* Case 2: One side mirror (Figure 7b)  
At position A (Figure 9A), it can be seen that the top of the boundary is still out of range, and some of the areas between the LiDAR and the mirror within the field of view of the LiDAR are undetected. A small amount of boundary reflection is seen on the other side of the mirror. At position B, there is no more negative space within the test boundary (Figure 9B). A significant amount of the reflection of the left boundary wall is now detected behind the surface of the mirror at the same distance from the mirror as the physical wall. Similar to case 1, specular reflection of the mirror was misinterpreted as light transmission through transparent medium; it was expected to observe the robot on the surface of the mirror when it passes. This observation was seen in some runs of this test. At position C, the reflection of the left wall boundary is detected behind the mirror and is well defined on the RViz visualization tool (Figure 9C). Some of the bottom boundary reflections are also seen. The robot travels slowly to increase the number of LiDAR scans. However, by observing the amount of detected boundary reflection, it is possible that if the robot slowed down further, complete boundary reflection would have been seen. Figure 8: RViz map of test case 1 at positions (**A–C**) where the mobile robot travels toward a plane mirror. Figure 7: Schematic showing the representation of test cases 1–4 with single or multiple mirrors. (**a**) One frontal mirror. (**b**) One side mirror. (**c**) Two parallel side mirrors. (**d**) One frontal mirror and two side mirrors. Case 3: Two side mirrors (Figure 7c)  
When the Turtlebot traveled in a straight line between two parallel mirrors, the maps of the boundary wall were seen on both sides behind both parallel mirrors; however, one mapped reflection was lower in map point density than the other (Figure 10A). The Turtlebot was continuously detected on the surface of one of the mirrors. At position B, the reflection of the boundary walls could be seen on both sides behind both mirrors (Figure 10B). It can be assumed that both mirrors map the reflection of opposite walls. In other words, the faulty interpretation of LiDAR to recognize reflective objects with transparent objects can be seen on both sides of the physical setup. Another interesting observation is that the robot was detected on only one of the mirrors.