# Computer Vision-Based Approach for Reading Analog Multimeter
## 4 Illustration of Reading the A-Meter  
After presenting the methodology of our approach with the framework and system setup in Section 2 and the angle detection of pointer in Section 3, a series of results of measuring a 1K\(\Omega\) resistor by the A-meter YF-370A are shown here to demonstrate the feasibility of the proposed approach. Figure 12a shows the original image (\(\mathbf{I}_{org}\)), where one 1K\(\Omega\) resistor is being measured by an A-meter YF-370A. The gray channel of Figure 12a was used for further processing, where its mean intensity was \(\bar{I}=131.1\). By template matching using Equation (8) with the template (\(\mathbf{T}_{A-meter}\)) given in Figure 6, \(rotation_{A-meter}=16.914^{\circ}\) was detected, where the center of \(ROI_{A-meter}\) was (1225.9, 1420.6), as depicted in Figure 12b. Then, the horizontal alignment image (\(\mathbf{I}_{adj}\)) was obtained by rotating the \(\mathbf{I}_{org}\) in Figure 12a about the center (1225.9, 1420.6) with \(-16.914^{\circ}\), as shown in Figure 12c. Next, by performing template matching using Equation (12) with the templates given in Figure 7a-c onto the \(\mathbf{I}_{adj}\), the \(\mathbf{R}_{IM}\) was located as the top region marked with the red rectangle in Figure 12d, where the selector arrow was also found using Equation (13), with the template given in Figure 8. The \(\mathbf{R}_{IM}\) was used later for the detection of the right-end \(\mathbf{R}_{right-end}\) and left-end \(\mathbf{R}_{left-end}\) of the scale. In this step, the detected selector arrow reported the rotation angle as \(\theta_{s}=314.194^{\circ}\). According to Equation (1) and the mapping table in Table 1, this \(\theta_{s}\in[297^{\circ},315^{\circ})\) indicates that the current selection represents the function name \"\(\Omega\times 10\)\"; \(F(\theta_{s})=17\) a nonlinear case; and \(A(\theta_{s})=10\) is a multiplier. Within the found \(\mathbf{R}_{IM}\), Figure 12e shows that the useful right-end \(\mathbf{R}_{right-end}\) and left-end \(\mathbf{R}_{left-end}\) of the scale were obtained by means of Equation (12) with the templates given in Figure 7d-f and Figure 7g-i, respectively. In this step, the coordinates of \(\mathbf{R}_{right-end}\) were found by \((x_{r1},y_{r1})=(761.2,248.1)\), \((x_{r2},y_{r2})=(970.6,247.3)\), \((x_{r3},y_{r3})=(762.0,452.1)\), and \((x_{r4},y_{r4})=(971.4,451.3)\), and those of \(\mathbf{R}_{left-end}\) were found by \((x_{l1},y_{l1})=(291.4,249.6)\), \((x_{l2},y_{l2})=(487.4,249.6)\), \((x_{l3},y_{l3})=(291.4,447.6)\), and \((x_{l4},y_{l4})=(487.4,447.6)\). Therefore, \(\theta_{r}=44.473^{\circ}\) according to Equation (16) and \(\theta_{l}=134.709^{\circ}\) according to Equation (17), respectively. In addition, by means of Equation (18), the spin center was obtained as \((x_{c},y_{c})=(625.0,586.6)\). According to the results obtained above, we the scanline length \(L=499.318\) (pixels) and \(\Delta\theta=0.128^{\circ}\), based on Equation (21), were used in our scanning process to detect the \(\theta_{p}\). As noted in Section 3.2, to detect the pointer, the scanning range needed to be wider than \(\theta_{R}\) in real applications. Thus, the process was scanned from \(\theta_{r}^{{}^{\prime}}=\theta_{r}-5^{\circ}\) to \(\theta_{l}^{{}^{\prime}}=\theta_{l}+5^{\circ}\) to produce the accumulation profile of \(A\) and the gradient profile of \(GA\), as shown in Figure 13a,b, respectively. In this example, itwo valleys obviously appeared (Figure 13a), which indicated the positions of \(\theta_{r}\) and \(\theta_{l}\), respectively. From the \(GA\)-profile in Figure 13b and according to Equation (20), the detected index was \(k=704\) with the corresponding \(\theta(704)=118.405^{\circ}\), which was just the detected pointer's position (\(\theta_{p}\)) in the current illustration.