# A Lightweight Visual Odometry Based on LK Optical Flow Tracking
## 3 Experiment and Analysis
The histogram compares the error parameters of the APE in the two systems, and the box diagram shows the fluctuation of the data. The histogram analysis shows that the supposed system in this paper outperforms the ORB-SLAM3 system in five of the APE error parameters, including the RMSE, minimum error (Min), median error (Median), mean error (Mean), and maximum error (Max). However, it is slightly inferior to the ORB-SLAM3 system in the standard error (Std), but the difference is relatively small. According to the box plot analysis, the data fluctuation of the proposed system is slightly smaller than that of the ORB-SLAM3 system. It shows that the positioning accuracies of the two systems are better under this sequence, and the differences among the various parameters in APE are small. However, on the whole, the positioning accuracy and stability of the proposed \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sequence**} & \multicolumn{2}{c}{**Average Time Consumption (s)**} & \multirow{2}{*}{**Improvement**} \\ \cline{2-3} \cline{5-4}  & **Ours** & & **ORB-SLAM3** \\ \hline fr1-xyz & **0.024** & 0.029 & **17.24\%** \\ fr1-room & **0.016** & 0.021 & **23.81\%** \\ fr1-desk2 & **0.013** & 0.019 & **31.58\%** \\ fr2-large & **0.015** & 0.022 & **31.82\%** \\ fr2-rpy & **0.022** & 0.027 & **18.52\%** \\ fr2-person & **0.024** & 0.034 & **29.41\%** \\ fr3-office & **0.014** & 0.019 & **26.32\%** \\ fr3-notx-near & **0.01** & 0.013 & **23.08\%** \\ fr3-tx-near & **0.022** & 0.029 & **24.14\%** \\ \hline office2 & **0.015** & 0.021 & **28.57\%** \\ office3 & **0.017** & 0.023 & **26.09\%** \\ living2 & **0.015** & 0.022 & **31.82\%** \\ living3 & **0.018** & 0.027 & **33.33\%** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of per frame average runtime. system in this paper are slightly better than that of ORB-SLAM3, and RMSE for translation is 0.021, which meets the requirements of positioning and map construction. Figure 9 shows the RPE comparison between the two systems under the fr1-desk2 sequence. Through the detailed analysis of the figure, it can be seen that all the RPE data of the proposed system are better than those of the ORB-SLAM3 system. So it can be concluded that the comprehensive performance of the proposed system is better than that of the ORB-SLAM3 system under this sequence. Figure 10 shows the comparison projected onto the \(x\)-\(o\)-\(z\) plane between the ground truth and the trajectories generated via the proposed system and the ORB-SLAM3 system under the office3 sequence. It can be seen from the figure that the trajectories generated by the two systems are consistent with the ground truth provided by the dataset, which indicates that both systems have achieved good performance under this sequence. However,  
Figure 8: Comparison of APE of sequence fr1-desk2. (**a**) Histogram; (**b**) box diagram. Figure 7: The trajectory position comparison diagram of fr1-desk2 sequence. as indicated by the red squares in the figure, the ORB-SLAM3 system has a large error. The reason is that the texture of the region is low and the key points are not rich enough, resulting in poor feature matching of the system. Because the proposed system tracks and matches the key points by the pyramid-based sparse optical flow method, more key points can be tracked in the area with lower texture, improving the accuracy and robustness of the system. Figures 11 and 12 show the comparisons of the APE and RPE of the two systems under the sequence, office2. Through specific analysis, we know that all the data of APE and RPE of the proposed system are better than those of the ORB-SLAM3 system, and the data fluctuation range is smaller. Figure 10: The trajectory position comparison diagram of office2 sequence. Figure 9: Comparison of RPE of sequence fr1-desk2. (**a**) Histogram; (**b**) box diagram. Figure 13 shows the comparison projected onto the two-dimensional plane between the ground truth and the trajectories generated by the proposed system and the ORB-SLAM3 system under the other sequences.