# Comparison of Tracking Techniques on 360-Degree Videos
## 3 Experiments
### Experiment Results  
To demonstrate qualitative tracking outputs of eight trackers on nine 360-degree video sequences, six representative snapshots with a fixed interval of time in each 360-degree video sequence are shown in detail in Figures 4-12. The tracking results of all trackers are marked as rectangular windows with different colors in each snapshot (MOSSE:yellow; MIL:blue; MedianFlow:purple; BOOST:turquoise; TLD:red; KCF:green; GOTURN:pink; CSRT:cyan). The video sequence 1 was captured by a moving biker. The tracking target was another bike with huge scale change, some viewpoint change, and minor lighting change over time. Among eight trackers, the CSRT, MIL, BOOST, and MOSSE trackers performed quite well, but other trackers lost the target in the middle of the sequence as shown in Figure 4. The video sequence 2 was captured by a moving motorcycle. The tracking target was a stadium on one side of the road. The building was occasionally occluded by trees and streetlamps. All trackers were affected by the occlusion problem and so only produced decent tracking results as shown in Figure 5. Especially, the MedianFlow tracker confused the tracking target with other obstacles. It suffered seriously from temporal occlusion in this sequence. The video sequence 3 was captured by a drone with an overlooking view of a lake. The tracking target was the roof of a green building. The shape of the target deformed dramatically due to the nature of 360-degree videos in an equirectangular format. Luckily, some trackers could still follow the target smoothly for a short period of time. Figure 4: Tracking results on 360-degree video sequence 1 (tracking windows with different colors: MOSSE MIL MedianFlow BOOST TLD KCF GOTURN CSRT). Figure 3: Flowchart of the proposed experiment to evaluate eight trackers on nine 360-degree videos. The video sequence 4 was captured by a drone flying around a lake harbor. The tracking target was a small boat docking at a pier. The scale of the target changed a lot over time as shown in Figure 7. Though the KCF and MOSSE trackers achieved a fair accuracy at the beginning, they lost the target in the middle of the sequence. Even worse, the GOTURN and TLD trackers got confused and tracked the wrong objects in the early stage. The video sequence 5 was captured by a drone flying along a lakeshoe. The tracking target was a lakeside building with a red roof. The scale of the building changed slowly over time, hence the MedianFlow tracker performed quite well. The sequence 5 contained another nature of 360-degree videos in that the tracking target disappeared from one side and reappeared on the other side of the panoramic image. Most trackers cannot recover from this problem. Interestingly, the TLD tracker correctly recovered the target as shown in the last snapshot of Figure 8. The video sequence 6 was captured by a drone flying across a lake. The tracking target was a fast-moving boat with apparent viewpoint change. With the problem of large motion in this sequence, only the GOTURN tracker obtained great results. In comparison, the KCF and MOSSE trackers lost the tracking target very early as shown in Figure 9.  
Figure 5: Tracking results on 360-degree video sequence 2 (tracking windows with different colors: MOSSE MIL MedianFlow BOOST TLD KCF GOTURN CCRT). Figure 6: Tracking results on 360-degree video sequence 3 (tracking windows with different colors: MOSSE MIL MedianFlow BOOST TLD KCF GOTURN CCRT). The video sequence 7 was captured by a moving biker. The tracking target was a large building with slow viewpoint change, and some partial occlusion. Although several trackers received decent scores, they were not really focused on the center of the building. Only the BOOST tracker accurately tracked the whole building throughout this sequence as shown in Figure 10. The video sequence 8 was captured by a drone flying on windy days. The characteristic of this sequence was camera shakiness which is a common problem on drone-recorded 360-degree videos.