Generalized Scale Factor Calibration Method for an Off-Axis Digital Image Correlation-Based Video Deflectometer.

Area of Science:

• Engineering
• Optics
• Measurement Science

Background:

• Accurate deflection monitoring of engineering structures using off-axis digital image correlation (DIC) relies on precise scale factor (SF) calibration.
• The SF converts pixel displacement to physical displacement, directly impacting measurement quality.

Purpose of the Study:

• To propose a generalized SF calibration model for off-axis DIC-based video deflectometers.
• To analyze the relationship between the proposed model and existing SF calibration methods.
• To compare the accuracy of different SF calibration methods.

Main Methods:

• Development of a generalized SF calibration model based on the distortion-free pinhole imaging model.
• Theoretical analysis of the proposed method's relationship with three common SF calibration methods.
• Experimental validation using indoor rigid body translation tests.

Main Results:

• The proposed SF calibration method can generalize existing methods under most conditions.
• The new method demonstrates superior accuracy when the camera's pitch angle exceeds 20°, focal length is over 25 mm, sensor pixel size is larger than 5 µm, or measurement points are far from the image center after deformation.

Conclusions:

• The generalized SF calibration model offers enhanced accuracy for off-axis DIC video deflectometry.
• This improved calibration is particularly beneficial for challenging imaging scenarios, leading to higher-quality displacement measurements in structural health monitoring.