Fig. 1. Schematic diagram of center point of ellipse calibration by five-point fitting

Fig. 2. Schematic diagram of isometric stage growth of Nd∶YVO₄ crystal rod

Fig. 3. Effect of different edge detection algorithms. (a) Original image; (b) Sobel; (c) Scharr; (d) Laplacian; (e) Canny

Fig. 4. Weighted pixel value and gradient analysis in different ray directions. (a) Direction 1; (b) direction 2

Fig. 5. Sample image of edge point detection of the crystal rod

Fig. 6. Modeling of center point calibration problem of crystal cross-section

Fig. 7. Schematic diagrams of radius as a function of angle. (a) Functions of different phases; (b) functions of different phases and vertical displacements

Fig. 8. Cross-section of crystal rod drawing with calibration center

Fig. 9. Schematic diagram of imaging model

Fig. 10. Simulation images. (a) Original image; (b) example of image sequence

Fig. 11. Convergence of calibration centers for different optimization algorithms. (a) 1°; (b) 3°; (c) 5°; (d) 9°; (e) 15°; (f) 45°

Fig. 12. Average error of center point calibration. (a) X-direction average error; (b) Y-direction average error

Fig. 13. Distribution of center points calibrated by different algorithms. (a) X-direction distribution; (b) Y-direction distribution

Fig. 14. Estimation of crystal rod cross-section dimensions by different algorithms. (a) Actual and estimated dimensions of the major axis; (b) actual and estimated dimensions of the minor axis