# Enhanced Detection of Subway Insulator Defects Based on Improved YOLOv5
## 3 Methods  
### Image Acquisition  
The distinct characteristics of subway environments necessitate specific protocols, including restricting access to tunnels, typically limited to authorized personnel during pre-dawn maintenance hours. The operational constraints of subways preclude the use of unmanned aerial vehicles for image capture, a technique otherwise employed in conventional railway settings. Compounding these challenges is the need for the prompt replacement of defective insulators, which impedes the collection of authentic defect imagery in situ. In response to these limitations, and to obtain a robust dataset of defective insulators, this study engineered a representative model of the contact network, meticulously mirroring the actual structure and dimensions of a functioning subway contact network. The insulators incorporated into this model comprised both damaged and pristine specimens, sourced from the Guangzhou subway system. A comparative analysis between the constructed model and the authentic contact network was undertaken, with correlating visuals presented in Figure 3.  
Upon the strategic configuration of the experimental framework and model, a diverse array of perspectives and proximities were employed to obtain a comprehensive dataset pertaining to the contact network insulators. Image acquisition was executed utilizing a Daheng ME2P-2621-4 GC-P camera, the specifications of which are delineated in Table 1.  
Within the constructed experimental simulation, image capture was primarily conducted during the early morning and evening hours under low-light conditions, mimicking the auxiliary illumination typically present in actual subway environments. Real-world parameters indicate a spatial range of 4 m to 6 m between the track and the contact wire, as evidenced by the 4-m tunnel height in the Guangzhou Metro Line 3 and a 6-m height in Line 18, with actual distances subject to variation due to angular imageic influences. This study, therefore, employed seven distinct shooting distances, ranging from 4 m to 6.5 m, in 0.5-m increments. Given the mobile nature of the detection equipment within the subway system, it is possible to secure images of insulators from multifaceted angles. Accordingly,  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Category** & **Parameter** \\ \hline Resolution & 5120 \(\times\) 5120 pixels \\ FPS & 4.5 \\ Pixel size & 2.5 μm \\ Pixel depth & 8 bit, 12 bit \\ Signal-to-noise ratio (SNR) & 35.65 dB \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of Daheng ME2P-2621-4 GC-P camera.  
Figure 3: Comparison of overhead contact systems (OCS) in real and experimental environments: (a) real environment; (b) experimental environment.  
the study utilized five shooting angles, dispersed at 22.5-degree intervals, spanning from 0 to 90 degrees. The predominant form of insulator impairment observed was structural damage (refer to Figure 4), with an observed size disparity ranging from 0.5 cm to 10.5 cm. The experimental dataset comprised a total of 1000 images, encompassing 647 instances of defective insulators and 353 instances of their intact counterparts.  
To assess the applicability of the model derived from the experimental dataset, this study conducted an evaluation using images captured in authentic environments. Specifically, 200 images were procured from Guangzhou Metro Line 3, as depicted in Figure 5. The imageic process employed a detection vehicle outfitted with identical camera and lighting apparatuses, both affixed to a gimbal capable of angular adjustment. Throughout its operation, the vehicle traversed the track, enabling the acquisition of insulator images from diverse perspectives.