Fig. 1. Flow chart of extraction method of solar meridian based on Hough transformation

Fig. 2. Principle of Hough transformation. (a) Rectangular coordinate system; (b) polar coordinate system

Fig. 3. Azimuth distribution model of sky polarized light

Fig. 4. Edge detection result of Canny operator

Fig. 5. Result of edge line feature detected by Hough transformation

Fig. 6. Feature area of solar meridian in different threshold ranges

Fig. 7. Simulation results of different methods. (a) Original image; (b) proposed method; (c) least square method

Fig. 8. Sample test results

Fig. 9. Mean value of absolute error

Fig. 10. Comparison of accuracy under different feature thresholds

Fig. 11. Comparison of measurement correctness

Fig. 12. Comparison of measurement precision