An Accurate Image Measurement Method Based on a Laser-Based Virtual Scale

Area of Science:

• Optical Engineering
• Metrology
• Computer Vision

Background:

• Image measurement techniques are accurate but often require complex calibration and are sensitive to environmental factors.
• Existing methods can be cumbersome, limiting their application in challenging environments.

Purpose of the Study:

• To develop a simple, robust, and accurate optical device for non-contact measurements.
• To create a virtual scale for mapping image coordinates to world coordinates.
• To achieve high-precision measurements at the sub-pixel level.

Main Methods:

• Designed a simple optical device emitting parallel beams to generate a virtual scale.
• Developed a theory ensuring scale robustness under uncertainty.
• Utilized the moving least squares (MLS) method to reconstruct a full-field scale map.

Main Results:

• The proposed method demonstrated high accuracy and reliability in experimental verifications.
• The system achieves sub-pixel measurement precision.
• The virtual scale is automatically calculated, simplifying the process.

Conclusions:

• The developed optical device offers a simple and effective solution for non-contact measurements.
• This approach is suitable for measuring geometric sizes and crack development in inaccessible structures like bridges and buildings.
• The system's robustness and ease of use make it a promising tool for structural health monitoring.