# A Fitting Recognition Approach Combining Depth-Attention YOLOv5 and Prior Synthetic Dataset
## 3 Hardware and Data
### Inspection Data  
The components of PTL system inspection mainly include towers, fittings, and power lines. Among them, the fittings are the most difficult task in power inspection: they are the most numerous in type and number of these three categories. Robot inspection is an excellent method for this difficult PTL inspection task. FPTLIR is a hybrid robot in the mentioned inspection robots [8]. Figure 3 shows the inspection paths of FPTLIR on the PTLs, which can be divided into four steps: flying up-line, walking along the line, crossing obstacles, and flying down-line. The high-quality data is collected when FPTLIR walks along the line. Figure 4 shows the position relationship between FPTLIR and fittings. O-XYZ, O-XYZ, O-XYZ, O-XYZ, Y-XYZ, and O-XYZXYZXYZ are the global coordinate system, the fitting coordinate system, and the robot coordinate system, respectively. The Z-axis of the global coordinate system is vertically upward, and the Y-axis is perpendicular to the transmission line. The \(z_{r}\)-axis of the robot coordinate system is perpendicular to the flying plane, and the \(y_{r}\)-axis is the same as the direction of travel in robot walking mode. The initial direction of the fitting coordinate system is the same as the global coordinate system. The coordinate origin of the fitting is at the most edge of the fixture. Since FPTLIR walks along the ground line to collect data, \(t_{y}\) and \(t_{z}\) are related to the power tower structure. \(t_{x}\) is the distance between FPTLIR and the fittings on the X-axis; \(\alpha\), \(\beta\), \(\gamma\) are the rotation angles of the fitting on the \(x_{i}\), \(y_{i}\) and \(z_{i}\) axes, respectively. \(l\) is the distance between the background and fittings on the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Component Name**} & \multicolumn{1}{c}{**Mode**} & \multicolumn{1}{c}{**Amount**} \\ \hline \multicolumn{2}{c}{FPTLIR body} & \begin{tabular}{c} Flying mode \\ Walking mode \\ \end{tabular} & \begin{tabular}{c} 1 \\ 1 \\ 1 \\ \end{tabular} \\ \hline \multirow{3}{*}{Cameras} & D-RGB cameras & \
\begin{tabular}{c} D435i \\ ZED \\ \end{tabular} &
\begin{tabular}{c} 1 \\ 1 \\ 1 \\ \end{tabular} \\ \cline{2-3}  & Inspection camera & SJ4000 & 1 \\ \hline \multirow{3}{*}{Controllers} & Central control & NVIDIA Jetson NX & 1 \\  & Walking mode control & STM32 & 1 \\ \cline{1-1}  & Flying mode control & PX4 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The key components of FPTLIR. Figure 2: The installation position of cameras. X-axis, and this distance is large, which is the reason for the large difference in depth maps between the fittings and the backgrounds. Figure 5 shows an RGB image, a depth map of a power tower and some usual fittings. (The infrared heat map is used here to illustrate the depth map because they are very similar.) The difference between the power tower and the background is very clear in the depth map. The depth information of the fittings (e.g., clamps, dampers, insulators) is included in the highlighted portion of the depth map. The large difference in depth information feature could improve the recognition accuracy and reduce the background misdetection when the robot recognizes the fittings. The inspection data of FPTLIR includes RGB images, depth maps, location information, walking path information, etc. As seen from FPTLIR's motion path in Figure 3, the collected data by FPTLIR is continuous in time and space, but different type data are not continuous. So, this information is matched in time and space, and a complete database of the PTL corridor can be obtained. The data collection is based on FPTLIR platform, and the high-quality data are collected when FPTLIR walks along the ground line. The collected data has the following characteristics:  
* The background of collected images by FPTLIR is mostly ground, and the data is continuously collected along the line to obtain a complete database of PTL corridor.