Three-dimensional measurement of object surfaces with complex shape and color distribution based on projection of color fringe patterns

A challenging issue associated with three-dimensional (3D) fringe patterns profilometry (FPP) is the unwrapping of phase maps resulting from color object surfaces. This paper proposes a new colorprojection-based 3D FPP, making use of the three primary color channels [i.e., red, green, and blue (RGB)] associated with digital projectors. One channel (e.g., red) is used for projecting sinusoidal fringes required by phase shift profilometry (PSP); the other two channels are employed for generating binary stripe patterns. In order to achieve reliable phase unwrapping, each fringe of the sinusoidal patterns is identified by a unique binary sequence. These sequences are then encoded by a channel-encoding scheme used in the area of communication. The encoded sequences are embedded in the binary coding stripe images, which are projected together with the sinusoidal patterns. The three image patterns are reflected by the object surface and captured by an RGB 3-CCD camera. The reflected sinusoidal patterns are employed to yield a wrapped phase map, and the binary stripe patterns are used to retrieve the encoded sequences, which are then decoded to yield the original binary sequences for phase unwrapping. Compared with existing color-encoded algorithms, the proposed approach uses binary codes instead of fringe color to identify the fringes, which are less sensitive to the disturbances caused by object surface color and illumination noises. Furthermore, use of the channel-coding scheme provides extra resistance to the disturbances caused by object surface color and illumination noises. Experimental results are presented to confirm the effectiveness of the proposed technique

Impact of meteorological factors on the COVID-19 transmission: A multicity study in China

The purpose of the present study is to explore the associations between novel coronavirus disease 2019 (COVID- 19) case counts and meteorological factors in 30 provincial capital cities of China. We compiled a daily dataset including confirmed case counts, ambient temperature (AT), diurnal temperature range (DTR), absolute humidity (AH) and migration scale index (MSI) for each city during the period of January 20th to March 2nd, 2020. First, we explored the associations between COVID-19 confirmed case counts, meteorological factors, and MSI using non-linear regression. Then, we conducted a two-stage analysis for 17 cities with more than 50 confirmed cases. In the first stage, generalized linear models with negative binomial distribution were fitted to estimate city-specific effects of meteorological factors on confirmed case counts. In the second stage, the meta-analysis was conducted to estimate the pooled effects. Our results showed that among 13 cities that have less than 50 confirmed cases, 9 cities locate in the Northern China with average AT below0 °C, 12 cities had average AHbelow4 g/m3, and one city (Haikou) had the highest AH (14.05 g/m3). Those 17 cities with 50 and more cases accounted for 90.6% of all cases in our study. Each 1 °C increase in AT and DTR was related to the decline of daily confirmed case counts, and the corresponding pooled RRs were 0.80 (95% CI: 0.75, 0.85) and 0.90 (95% CI: 0.86, 0.95), respectively. For AH, the association with COVID-19 case counts were statistically significant in lag 07 and lag 014. In addition,we found the all these associations increased with accumulated time duration up to 14 days. In conclusions, meteorological factors play an independent role in the COVID-19 transmission after controlling population migration. Local weather condition with low temperature, mild diurnal temperature range and low humidity likely favor the transmission

Improved method for estimation of multiple parameters in self-mixing interferometry

There are two categories of applications for self-mixing interference (SMI)-based sensing: (1) estimation of parameters associated with a semiconductor laser (SL) and (2) measurement of the metrological quantities of the external target. To achieve high resolution sensing, each category of applications requires knowledge from the other. This paper proposes an improved method that can simultaneously measure the parameters of an SL and the target movement in arbitrary form. Starting with the existing SMI model, we derive a new matrix equation for the measurement. The measurement matrix is built by employing all the available data samples obtained from an SMI signal. The total least squares estimation approach is used to estimate the parameters. The proposed method is verified by both simulations and experiments. (C) 2015 Optical Society of Americ

Removing the impulsive noise contained in a self-mixing interferometry system using outlier detection

Impulsive noise is a major problem that seriously degrades the performance of self-mixing interferometry (SMI). A new method to rectify this issue is proposed. First, an outlier detection approach is employed to detect the data samples corrupted by the impulsive noise, and then the SMI signal waveform is rectified by means of least square (LS) curve fitting. The results show that the proposed method can effectively remove the impulsive noise without introducing distortion to the original waveform and thus lead to improvement in the performance of an SMI system

High rate serially concatenated codes with low error floors

Serial concatenation of Hamming codes and an accumulator has been shown to achieve near capacity performance at high code rates. However, these codes usually exhibit poor error floor performance due to their small minimum distances. To overcome this weakness, we propose to replace the outer Hamming codes by product codes constructed from Hamming codes and single-parity-check codes. In this way, the minimum distance of the outer code can be doubled, which is expected to increase the minimum distance of the serially concatenated code and thus to improve error floor performance. Three-dimensional EXIT chart is used for their convergence analysis and the derived thresholds are shown to be close to Shannon limit. Low weight distance spectrum of the proposed code is also calculated and compared with the original code. Simulation results show that the proposed codes can lower the error floor by two orders of magnitudes without waterfall performance degradation at short block length