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Video Basics
Published in Wes Simpson, Video Over IP, 2013
HDsignals use a different aspect ratio for the video image. For SD television signals (and many common computer displays), the aspect ratio is 4:3, meaning that the video image is 4 units wide by 3 units high. For most HDTV signals, the aspect ratio is 16:9, which is one-third wider than 4:3. The wider aspect ratio of HDTV was chosen in part to make it closer to the aspect ratios used in most films. Figure 3-6 gives a comparison of the different image sizes and aspect ratios for popular SD and HD video formats.
Structure of open-channel flows through an array of square cylinders
Published in Urban Water Journal, 2022
Marina Oukacine, Frederique Larrarte, Nicole Goutal
Bonakdari et al. (2008) and Lassabatere et al. (2013) found that, in narrow channels, the vertical velocity satisfies three criteria, namely: the mean vertical velocity is zero at both the bottom and the free surface and negative at the center. It is possible to calculate the dimensionless position εdip, at which the velocity is maximized on the vertical profile of the mean longitudinal velocity: εdip = zmax/H, where zmax is the position of the maximum mean longitudinal velocity. Several empirical equations serve to determine the εdip position as a function of the aspect ratio (Wang and Cheng 2006; Yang, Tan, and Lim 2004; Bonakdari et al. 2008). Table 3 compares the aspect ratio Ar defined with the standard definition with a ratio Ar’ that uses the width between two lines of square cylinders. The equation found in Bonakdari et al. (2008) equation has been used to calculate εdip. For the E093 and 098 cases, the measured and experimental values range between 0.4 and 0.5, which is roughly the standard position of the mean velocity flow (0.40) in the international standard ISO 748 regarding the measurement of liquid flow in open channels.
Robotic surgery remote mentoring via AR with 3D scene streaming and hand interaction
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2023
Yonghao Long, Chengkun Li, Qi Dou
To thoroughly evaluate the overall latency, we test our system under different common-used video resolutions from to . Specifically, Table 2 reports the HoloLens update frame rate in mentor side, which can achieve satisfying real-time update speed () with standard definition resolution (). Even when given high definition resolution (), the HoloLens can still achieve acceptable update rate () to fulfill the low requirement of mentor side for basic visual-hand interaction. We also evaluate the end-to-end closed-loop latency for operation side and distinguish different components’ latency, as shown in Figure 4. The total latency ranges from to with different resolution with even the highest latency is within the acceptable latency () in terms of surgeon’s perception of safety according to prior studies (Marescaux et al. 2001; Lacy et al. 2019), thus feasible and efficient for remote mentoring. We further discuss the latency of each component. Relative constant time for console overlaying is observed, as GPU can visualise and overlay guidance in paralleled. And the disparity computing and HoloLens rendering time decrease dramatically when given lower resolution, showing the high efficiency of our system.