Abstract
This investigation is aiming at the development of a method for in-situ 3D imaging and reconstructions of objects in the rain. The proposed method is based on the use of monochromatic sinusoidal fringe pattern generated by the designed optical system, the polarization technique, and the Fourier-transform-based algorithm of reconstruction. Based on the theoretical analyses and experimental results, it shows that the generated laser-beam-based signal keeps being coherent until reaching the observed object. The coherence of the projected sinusoidal signal is the key feature of the proposed method and ensures the accuracy of measurement and reconstruction of objects under rainy conditions. Moreover, the effects resulted from the spectral absorption and multiple scattering on the propagation of the projected sinusoidal fringe pattern in the rain can be removed using the polarization technique. The developed method is capable of obtaining accurate 3D reconstructions of the objects under rainy conditions together with background illumination, the multiply-scattered light, the vibration from environmental influences including the wind, and the inhomogeneous medium of rain. The application of this method does not suffer the limitation of focusing, precise synchronization, and the speed of measurement that might be a problem for the time-of-flight technique and digital-light-processing-based profilometry.
Highlights
T HE methods and technologies for non-contact and highresolution shape measurement of three-dimensional (3D)Manuscript received November 10, 2021; revised December 29, 2021; accepted January 11, 2022
Mathematical derivations, and experimental results completed in this study, we have demonstrated that reliable measurements and accurate reconstructions can be obtained for determining 3D surface shapes of observed objects in the rain based on the combination of laserbeam-based sinusoidal fringe projection, the polarization technique, the optical filtering technique, and the Fourier-transformbased algorithm of reconstruction
The optical filtering technique has to be employed if the background illumination exists, while the effects resulted from the spectral absorption and multiple scattering on the propagation of the projected sinusoidal fringe pattern generated by the designed optical system in the rain can be mostly removed using the polarization technique
Summary
T HE methods and technologies for non-contact and highresolution shape measurement of three-dimensional (3D)Manuscript received November 10, 2021; revised December 29, 2021; accepted January 11, 2022. Even the passive technique, such as the stereo-vision approach, is relatively simple and has no need for active illumination on the object being observed, the development of accurate method and efficient algorithm for completing stereo matching on two images is still being a challenging issue [4], [5]. The popular encoding methods include binary coding [6], sinusoidal phase encoding [7], [8], binary defocusing [9], [10], triangular phase-shifting method [11], and color coded structured patterns [12], [13] Those encoding methods are mostly based on the computer-controlled DMD-chip-based digital-light-processing (DLP) projector, which suffers from the limitations such as the requirement of precise synchronization, speed limit of measurement, and the nonlinear gamma effect of the DLP projection [14]. We have noticed that the recently developed stereo-vision-based
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