3D Shape Measurement Based on the Phase Shifting and Stereovision methods
MetadataShow full item record
This dissertation is focused on improving the performance of the 3D shape measurement systems based on the digital fringe projection, phase shifting, and stereovision techniques. New camera and projector models and calibration algorithms as well as a novel system design based on a combined phase shifting and stereovision method are introduced. The first part of this dissertation introduces systems based on the digital fringe projection and phase shifting techniques. The effect of lens distortion on both the camera and projector is modeled based on careful calibration. Radial and tangential distortion parameters of different orders are analyzed and the right combination of parameters is chosen to provide an optimal performance. Then a real-time system is designed based on this nonlinear calibration method, which achieves a maximum speed of 60 Hz. A new quality-map guided phase unwrapping algorithm is developed to address the phase ambiguity problem of the previous phase unwrapping algorithm, thus significantly enhancing the reliability of the system. In the second part of this dissertation, a novel design, which combines the phase shifting and stereovision techniques, is proposed to eliminate errors caused by inaccurate phase measurement. This method uses two cameras, which are set up for stereovision and one projector, which is used to project fringe patterns onto the object. Fringe images are taken by the two cameras simultaneously. The errors due to inaccurate phase measurement are significantly reduced because the two cameras produce phase maps with the same phase errors. The use of a visibility-modulated fringe pattern is also proposed to reduce the number of images required by this combined method, thus making the measurement of dynamically changing objects possible. A color system is designed to further improve the speed of this system. By utilizing color devices, one color fringe image is sufficient to reconstruct a 3D model instead of three black and white images. Finally, a portable 3D shape measurement system based on this combined phase shifting and stereovision method is proposed, which can be used to measure large objects.