scholarly journals Transparent Object Shape Measurement Based on Deflectometry

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 548
Author(s):  
Zhichao Hao ◽  
Yuankun Liu
Keyword(s):  
Data Acquisition ◽  
Phase Measurement ◽  
Focal Length ◽  
Three Dimensional ◽  
Normal Direction ◽  
Calibration Data ◽  
Actual Measurement ◽  
Temporal Phase ◽  
Convex Lens ◽  
Normal Orientation

This paper proposes a method for obtaining surface normal orientation and 3-D shape of plano-convex lens using refraction stereo. We show that two viewpoints are sufficient to solve this problem under the condition that the refractive index of the object is known. What we need to know is that (1) an accurate function that maps each pixel to the refraction point caused by the refraction of the object. (2) light is refracted only once. In the simulation, the actual measurement process is simplified: light is refracted only once; and the accurate one-to-one correspondence between incident ray and refractive ray is realized by known object points. The deformed grating caused by refraction point is also constructed in the process of simulation. A plano-convex lens with a focal length of 242.8571 mm is used for stereo data acquisition, normal direction acquisition, and the judgment of normal direction consistency. Finally, restoring the three-dimensional information of the plano-convex lens by computer simulation. Simulation results suggest that our method is feasibility. In the actual experiment, considering the case of light is refracted more than once, combining the calibration data acquisition based on phase measurement, phase-shifting and temporal phase-unwrapping techniques to complete (1) calibrating the corresponding position relationship between the monitor and the camera (2) matching incident ray and refractive ray.

scholarly journals High-Quality Pixel Selection Applied for Natural Scenes in GB-SAR Interferometry

2021 ◽  
Vol 13 (9) ◽  
pp. 1617
Author(s):  
Yunkai Deng ◽  
Weiming Tian ◽  
Ting Xiao ◽  
Cheng Hu ◽  
Hong Yang
Keyword(s):  
Phase Measurement ◽  
High Amplitude ◽  
Sar Interferometry ◽  
Spatial Density ◽  
Natural Scenes ◽  
Sar Images ◽  
High Quality ◽  
Temporal Phase ◽  
Permanent Scatterers ◽  
High Phase

Phase analysis based on high-quality pixel (HQP) is crucial to ensure the measurement accuracy of ground-based SAR (GB-SAR). The amplitude dispersion (ADI) criterion has been widely applied to identify pixels with high amplitude stability, i.e., permanent scatterers (PSs), which typically are point-wise scatterers such as stones or man-made structures. However, the PS number in natural scenes is few and limits the GB-SAR applications. This paper proposes an improved method to take HQP selection applied for natural scenes in GB-SAR interferometry. In order to increase the spatial density of HQP for phase measurement, three types of HQPs including PS, quasi-permanent scatter (QPS), and distributed scatter (DS), are selected with different criteria. The ADI method is firstly utilized to take PS selection. To select those pixels with high phase stability but moderate amplitude stability, the temporal phase coherence (TPC) is defined. Those pixels with moderate ADI values and high TPC are selected as QPSs. Then the feasibility of the DS technique is explored. To validate the feasibility of the proposed method, 2370 GB-SAR images of a natural slope are processed. Experimental results prove that the HQP number could be significantly increased while slightly sacrificing phase quality.

Integrated Microcomputer-LDV Instrumentation for Studying Finite Wing Aerodynamics

1993 ◽  
Author(s):  
Abdollah Khodadoust
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Data Acquisition ◽  
Fiber Optic ◽  
Three Dimensional ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Ice Accretion ◽  
Wing Model ◽  
Finite Wing

Abstract The effect of a simulated glaze ice accretion on the flow field of a three-dimensional wing is studied experimentally. A PC-based data acquisition and reduction system was used with a four-beam two-color fiber-optic laser Doppler velocimeter (LDV) to map the flow field along three spanwise cuts on the model. Results of the LDV measurements on the upper surface of the finite wing model without the simulated glaze ice accretion are presented for α = 0 degrees at Reynolds number of 1.5 million. Measurements on the centerline of the clean model compared favorably with theory.

scholarly journals RECONSTRUCTION OF INDOOR MODELS USING POINT CLOUDS GENERATED FROM SINGLE-LENS REFLEX CAMERAS AND DEPTH IMAGES

2015 ◽  
Vol XL-4/W5 ◽  
pp. 99-102
Author(s):  
F. Tsai ◽  
T.-S. Wu ◽  
I.-C. Lee ◽  
H. Chang ◽  
A. Y. S. Su
Keyword(s):  
Data Processing ◽  
Data Acquisition ◽  
Three Dimensional ◽  
Point Clouds ◽  
Data Acquisition System ◽  
Acquisition System ◽  
Indoor Environments ◽  
Single Lens ◽  
Processing Procedure ◽  
Data Processing Procedure

This paper presents a data acquisition system consisting of multiple RGB-D sensors and digital single-lens reflex (DSLR) cameras. A systematic data processing procedure for integrating these two kinds of devices to generate three-dimensional point clouds of indoor environments is also developed and described. In the developed system, DSLR cameras are used to bridge the Kinects and provide a more accurate ray intersection condition, which takes advantage of the higher resolution and image quality of the DSLR cameras. Structure from Motion (SFM) reconstruction is used to link and merge multiple Kinect point clouds and dense point clouds (from DSLR color images) to generate initial integrated point clouds. Then, bundle adjustment is used to resolve the exterior orientation (EO) of all images. Those exterior orientations are used as the initial values to combine these point clouds at each frame into the same coordinate system using Helmert (seven-parameter) transformation. Experimental results demonstrate that the design of the data acquisition system and the data processing procedure can generate dense and fully colored point clouds of indoor environments successfully even in featureless areas. The accuracy of the generated point clouds were evaluated by comparing the widths and heights of identified objects as well as coordinates of pre-set independent check points against in situ measurements. Based on the generated point clouds, complete and accurate three-dimensional models of indoor environments can be constructed effectively.

K-space filter effect in three-dimensional contrast MR angiography

1997 ◽  
Vol 38 (1) ◽  
pp. 173-175 ◽  
Author(s):  
K. Ito ◽  
J. Kato ◽  
S. Okada ◽  
T. Kumazaki
Keyword(s):  
Contrast Agent ◽  
Data Acquisition ◽  
Mr Angiography ◽  
Three Dimensional ◽  
Mr Images ◽  
Acquisition Period ◽  
Filter Effect ◽  
Flowing Material ◽  
Space Filter

Purpose: In three-dimensional (3-D) contrast MR angiography, temporal misregistration between the data acquisition period and the arrival of the contrast agent in the target vessels is thought to degrade the quality of the reconstructed images. The purpose of this study was to demonstrate and investigate this effect in phantom experiments. Material and Methods: MR images of a phantom tube were evaluated with flowing materials of water or Gd-DTPA solution by changing from water to Gd-DTPA solution halfway through the data acquisition period. Results: While no signal could be acquired with a stream of water in the tube, a clear signal was obtained with a flow of Gd-DTPA solution. Blurring and ghost artifacts surrounding the tube along the phase-encoding direction were observed when the flowing material was changed from water to Gd-DTPA solution halfway through the data acquisition period. Conclusion: K-space filter effect occurs during 3-D contrast MR angiography owing to the transient passage of the contrast agent, and this effect causes spatial artifacts in the reconstructed images.

Variable Focus Three-Dimensional Laser Digitizing System

1995 ◽  
Author(s):  
David G. Alciatore ◽  
Ronald M. Pasquini
Keyword(s):  
Focal Length ◽  
Single Point ◽  
Three Dimensional ◽  
Range Data ◽  
State University ◽  
Focus Laser ◽  
New Approach ◽  
Colorado State University ◽  
Significant Step ◽  
Variable Focus

Abstract This paper describes a new three-dimensional scanning technology which is being developed at Colorado State University. Unlike other laser-based scanners which use active or passive triangulation to obtain surface range data, the new variable focus laser digitizing system (VFLDS) uses the principles of optical focal length to measure surface range data. This system should represent a significant step forward in speed and simplicity over current laser-based single point digitizing systems while retaining all of their advantages. The goal of the initial research presented here is to produce preliminary results which will prove the viability of this new approach.

scholarly journals Temporal phase unwrapping using deep learning

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Wei Yin ◽  
Qian Chen ◽  
Shijie Feng ◽  
Tianyang Tao ◽  
Lei Huang ◽  
...  
Keyword(s):  
Machine Learning ◽  
Deep Learning ◽  
High Frequency ◽  
Phase Unwrapping ◽  
Motion Artifacts ◽  
Error Sources ◽  
Actual Measurement ◽  
Temporal Phase ◽  
Fringe Patterns ◽  
Frequency Phase

AbstractThe multi-frequency temporal phase unwrapping (MF-TPU) method, as a classical phase unwrapping algorithm for fringe projection techniques, has the ability to eliminate the phase ambiguities even while measuring spatially isolated scenes or the objects with discontinuous surfaces. For the simplest and most efficient case in MF-TPU, two groups of phase-shifting fringe patterns with different frequencies are used: the high-frequency one is applied for 3D reconstruction of the tested object and the unit-frequency one is used to assist phase unwrapping for the wrapped phase with high frequency. The final measurement precision or sensitivity is determined by the number of fringes used within the high-frequency pattern, under the precondition that its absolute phase can be successfully recovered without any fringe order errors. However, due to the non-negligible noises and other error sources in actual measurement, the frequency of the high-frequency fringes is generally restricted to about 16, resulting in limited measurement accuracy. On the other hand, using additional intermediate sets of fringe patterns can unwrap the phase with higher frequency, but at the expense of a prolonged pattern sequence. With recent developments and advancements of machine learning for computer vision and computational imaging, it can be demonstrated in this work that deep learning techniques can automatically realize TPU through supervised learning, as called deep learning-based temporal phase unwrapping (DL-TPU), which can substantially improve the unwrapping reliability compared with MF-TPU even under different types of error sources, e.g., intensity noise, low fringe modulation, projector nonlinearity, and motion artifacts. Furthermore, as far as we know, our method was demonstrated experimentally that the high-frequency phase with 64 periods can be directly and reliably unwrapped from one unit-frequency phase using DL-TPU. These results highlight that challenging issues in optical metrology can be potentially overcome through machine learning, opening new avenues to design powerful and extremely accurate high-speed 3D imaging systems ubiquitous in nowadays science, industry, and multimedia.

Sign in / Sign up

Export Citation Format

Share Document