# Automatic Reading Algorithm of Substation Dial Gauges Based on Coordinate Positioning
## 1 Introduction  
With the rapid development of the national economy, the demand for electricity in modern society is increasing. Therefore, the power industry has put forward higher and higher requirements for the safe, reliable and stable operation of power systems. Any error in the power system may lead to the occurrence of power accidents, which endangers the stability and routine operation of the whole power system [1]. The operating status of the equipment in a substation is judged based on each measurement datum. In order to ensure the safe and stable operation of a substation, the meters must be inspected regularly and repaired in time. However, the traditional inspection method is usually manual inspection, which brings problems of low efficiency, low precision and increased time consuming. In addition, the staff's vision, attitude and other personal factors will also affect the reading results. In some inclement weather, when real-time readings cannot be performed manually, it may affect the operation of the entire substation [2, 3]. The further development of computer technology and the improvement of the smart grid make the intelligization of substations a future development trend. At present, more and more substations use inspection robots for inspections, instead of manual inspections, which suffered from heavy and dangerous tasks. The inspection robot is equipped with visible light cameras, infrared thermal imaging cameras and other devices to realize the intelligent identification and linkage of the facilities in the station. At the same time, multiple inspection modes are adopted to realize 7\"24 h unmanned inspections [4]. It can also achieve real-time data collection, data transmission and intelligent early warnings, which ensure the safe and stable operation of the power grid [5]. Therefore, robot inspections in substations will surely replace manual inspections. Dial gauges with a simple structure, good cold-proofand waterproof performance are utilized in the electromagnetic interference environment of the substation. In addition, the barometers and thermometers used in substations commonly are suitable for mechanical pointer structures. A large number of dial gauges are used in substations, and they will be irreplaceable for a long time. The realization of the automatic reading of pointer instruments is a necessary condition for intelligent substations. Therefore, it has broad research prospects. Many automatic reading algorithms of dial gauges based on machine vision have been proposed. [PERSON] et al. [6] detected the position of the industrial resistance meter by using the image difference after image preprocessing. [PERSON] et al. [7] proposed a method of meter identification based on the area cumulative histogram. The position of the meter is obtained through the calculation of the histogram. This method is not to obtain the instrument directly from the image, as there will be errors in the conversion process, causing low reading accuracy. [PERSON] et al. [8] used a cloud based visual attention objects detection method to extract the interest pointer area, and then used the projection method to obtain the pointer deflection direction and angle for calculation. It reduced the effect of illumination but increased the amount of calculation, which leads to low efficiency. [PERSON] et al. proposed a novel reading method in [9], which can identify meter images under different brightness intensity and camera angles, and has good robustness. In order to prevent the collected meter from being deformed, [PERSON] et al. [10] presented an eight chain code shape to represent the pixel image shape, and used a binarization threshold determination method based on the symmetry degree to solve the pointer interference. Although the threshold-based segmentation method is efficient, it is easily affected by light. A reading method of analog multimeters was proposed by [PERSON] et al. in [11], which mainly depends on information from the arrow on the function selector and the pointer on the instrument meter.