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The feature points of the dot matrix calibration plate are evenly spaced circles. The center coordinates are determined by ellipse fitting; the accuracy of the center depends on the sharpness of the circle's edges and the degree of distortion.

Unlike a checkerboard pattern, the center of the circle is "calculated" through mathematical fitting, rather than being directly determined by geometric boundaries.

This design has several key advantages: It remains an ellipse even under perspective distortion: When the camera is tilted, the circle becomes an ellipse, but the center of the ellipse remains the same as the center of the circle (this mathematical property is crucial). It's better suited for large-angle calibration: The center can still be accurately extracted even at a 45° tilt. It has a denser density of feature points: More feature points can be placed within the same area.

Key features: Ellipse fitting for center extraction: Utilizing the property that perspective transformation does not change the position of the ellipse's center, accuracy is guaranteed. Strong resistance to perspective distortion: Feature points can still be accurately extracted even when shooting at an angle. Suitable for industrial environments: It has more lenient requirements for installation angles compared to a checkerboard pattern.

Checkerboard Pattern vs. Dot Grid

Feature Extraction Accuracy: 0.01~0.05px vs. 0.01~0.1px

Perspective Distortion Resistance: Weak vs. Stronger (Ellipse Fitting)

Tilting Tolerance Angle: ≤30° vs. ≤45°

Occlusion Tolerance: Low vs. Medium

Software Support: Wide vs. Wide

Calibration Board Cost: Medium vs. Medium