## 3 Monitoring Point Selection and Anomalous DATA Detection  
### Selection of Monitoring Points  
A comprehensive analysis of the substantial monitoring data concerning main girder deflection obtained from the monitoring system of a real bridge was conducted. A portion of the data was selected for further study. The remainder of the paper enumerates the primary girder deflection monitoring data of the aforementioned bridge from 4:00 on 11 October 2023 to 10:00 on 12 October 2023, along with the results of the ensuing analysis.  
Main girder deflection is a visual manifestation of the structural mechanical behavior characteristics of large-span steel truss girder bridges. It is also an important index that affects the normal use of steel truss girder bridges. In the monitoring process, specific correlations in deflection are evident between measurement points at varying locations. When the relative distance between measurement points falls within the optimal range, the correlation is pronounced, and the data reconstruction accuracy is enhanced [23].  
To ensure the accuracy and reliability of the deflection data repair, the six deflection monitoring points shown in Figures 2 and 3 were selected for the study. Specifically, measurement points 1 and 2 are situated within the same cross-section in the primary girder span, while measurement points 3, 4, 5, and 6 are positioned in the 3/8 and 5/8 cross-sections of the main span, adjacent to the measurement points in the main girder span.  
Figure 1: Steel truss bridge elevation (m).  
Figure 2: Elevation layout of deflection monitoring points of main beam (m).  
The employment of correlation heat maps as a pivotal instrument for the preliminary analysis of deflection monitoring data facilitates the expeditious identification of sensor monitoring data at pivotal locations of steel truss bridges (e.g., in the middle of the main girder spans), which are indispensable for the evaluation of the bridge's overall performance [24]. Figure 4 shows the correlation heat map for the six measurement points.  
As demonstrated in Figure 4, the correlation coefficient of the two-by-two cross cells of points 1, 2, and 3 is 0.98, which is nearly 1, suggesting a high degree of linear correlation. From a color perspective, the right side of the color scale indicates that the closer the value is to 1, the deeper the color. The color of the corresponding cells of the three points is consistent with the color scale of the area near 1, which intuitively reflects the strong correlation. A close examination reveals a high degree of correlation among these three monitoring points, with a notable synchronization in the trend of their data changes.  
Consequently, guided by the correlation heat map, three deflection monitoring points (point 1, point 2, and point 3) with high correlation were selected for focused analysis, thereby establishing a data foundation for the subsequent exclusion and localization of anomalous data, as well as the assessment of the repair effect. Given that monitoring point 2 is located in the middle of the main girder span of the bridge and has the most significant structural response to the bridge's deflection, point 2 was selected as the target repair point.