High-accuracy cross-media 3D measurement based on a ray model with unknown refractive

Area of Science:

• Optical Metrology
• 3D Measurement
• Image Processing

Background:

• Accurate 3D measurements are crucial for relic conservation and restoration.
• Protective enclosures are often necessary, introducing refractive media that distort measurements.
• Existing methods struggle with unknown refractive indices, leading to errors.

Purpose of the Study:

• To develop a general-purpose calibration and reconstruction method for 3D measurement through unknown refractive media.
• To achieve high-accuracy 3D dimensional data without refraction errors.
• To enable precise measurements within protective enclosures for applications like artifact preservation.

Main Methods:

• A ray model is employed to directly determine height and lateral coordinates using phase information.
• A mapping is established between imaging plane pixels and emitted light rays.
• A subsequent mapping links phase data to height, allowing direct coordinate determination.

Main Results:

• A fringe projection profilometry (FPP) system was built using a glass box and calibration target.
• 3D measurements were successfully performed on a standard plane and a sphere.
• The proposed method demonstrated significant effectiveness and high measurement accuracy.

Conclusions:

• The developed method accurately performs 3D measurements in the presence of unknown refractive media.
• This technique eliminates refraction errors, providing reliable dimensional data.
• The approach is effective for applications requiring precise measurements within protective enclosures.