Congjun Wang

Pre-calibration-free 3D shape measurement method based on fringe projection

This paper presents a pre-calibration-free 3D shape measurement method based on fringe projection. Unlike ordinary methods, it performs calibration and 3D shape measurement concurrently. The captured phase-coded fringe images are utilized to obtain homogenous control points from two camera viewpoints, and the rough 3D structure of these points can be retrieved. Further, a constrained non-linear least-squares optimization model is established to determine the in situ geometry of the optical components, and then, the 3D scene is reconstructed. This method provides an accurate 3D shape measurement capability even during disturbance of the optical geometry. Moreover, not requiring a preliminary calibration process makes the system ultra-flexible. The performance of this method was verified by experiments.

A prototype system for high precision 3D measurement based on grating method

In this paper a 3D shape measurement system based on the grating method was developed. The system consists of two CCD cameras and a DLP projector. The multi-frequency heterodyne principle was presented to overcome the unwrapping problem of phase functions, and a phase-to-coordinates conversion algorithm was proposed to reconstruct the 3D geometry from the unwrapped phase map. To demonstrate the performance of this 3D measurement system, a face model was measured, and the reconstructed 3D geometric surface is very smooth with details. Additionally, a ladder with one step was measured. The result shows the system can measure the discontinuous object and get high measurement precision.

High-speed FPGA-based phase measuring profilometry architecture

This paper proposes a high-speed FPGA architecture for the phase measuring profilometry (PMP) algorithm. The whole PMP algorithm is designed and implemented based on the principle of full-pipeline and parallelism. The results show that the accuracy of the FPGA system is comparable with those of current top-performing software implementations. The FPGA system achieves 3D sharp reconstruction using 12 phase-shifting images and completes in 21 ms with 1024 × 768 pixel resolution. To the best of our knowledge, this is the first fully pipelined architecture for PMP systems, and this makes the PMP system very suitable for high-speed embedded 3D shape measurement applications.

A hand-held, high-resolution 3D shape measurement system using structured and unstructured illumination

This paper presents a high-resolution 3D shape acquisition method for developing hand-held 3D measurement system by projecting structured and unstructured patterns. The structured patterns consist of three-step phase-shifting fringe patterns, and the phase can be computed pixel by pixel to achieve high-resolution 3D measurement, and the phaseshifting method commonly requires many additional images to implement a phase unwrapping procedure for obtaining absolute phase value and removing the correspondence ambiguity, but it would slow down the measurement speed and limits its applications in fast 3D measurement. To address this problem, an unstructured pattern using random speckle is employed to reject wrong correspondence and promises a correct 3D result. Therefore, only four images are required to reconstruct one 3D point cloud, which is suitable for fast 3D measurement in hand-held systems. Moreover, the proposed method can be speed up by parallel computing technology for real-time data processing. The experiments verify the performance of the proposed method.