Structured Light 3D Reconstruction

Overview

This project implements a complete structured-light 3D scanner using phase-shifting fringe projection profilometry (FPP). Target applications include quality control of precision machined parts and reverse engineering.

Principle

A DLP projector casts sinusoidal fringe patterns onto the object surface:

where $A$ is background illumination, $B$ is modulation amplitude, $\phi$ is the phase encoding depth, and $N$ is the number of phase steps (we use $N = 4$).

Phase Retrieval

Using four-step phase-shifting, the wrapped phase is recovered as:

Phase unwrapping is performed using a multi-frequency heterodyne approach. Two additional fringe frequencies $f_1$ and $f_2$ generate a synthetic wavelength:

This extends the unambiguous measurement range to cover the full object depth range.

Calibration

Camera and projector are calibrated using Zhang's planar checkerboard method. The stereo calibration produces the fundamental matrix $\mathbf{F}$ and the projection matrices $\mathbf{P}_c$, $\mathbf{P}_p$ used for triangulation.

Results

| Specification | Value | |---|---| | Accuracy (RMS) | 20 μm | | Point density | ~2M points per scan | | Measurement volume | 200 × 150 × 50 mm | | Scan time | 1.2 s |