Search for: All records

Various goodness-of-fit tests are designed based on the so-called information matrix equivalence: if the assumed model is correctly specified, two information matrices that are derived from the likelihood function are equivalent. In the literature, this principle has been established for the likelihood function with fully observed data, but it has not been verified under the likelihood for censored data. In this manuscript, we prove the information matrix equivalence in the framework of semiparametric copula models for multivariate censored survival data. Based on this equivalence, we propose an information ratio (IR) test for the specification of the copula function. The IR statisticis constructed via comparing consistent estimates of the two information matrices. We derive the asymptotic distribution of the IR statistic and propose a parametric bootstrap procedure for the finite-sample P-value calculation. The performance of the IR test is investigated via a simulation study and a real data example. 

Recent advances in computer vision algorithms and video streaming technologies have facilitated the development of edge-server-based video analytics systems, enabling them to process sophisticated real-world tasks, such as traffic surveillance and workspace monitoring. Meanwhile, due to their omnidirectional recording capability, 360-degree cameras have been proposed to replace traditional cameras in video analytics systems to offer enhanced situational awareness. Yet, we found that providing an efficient 360-degree video analytics framework is a non-trivial task. Due to the higher resolution and geometric distortion in 360-degree videos, existing video analytics pipelines fail to meet the performance requirements for end-to-end latency and query accuracy. To address these challenges, we introduce the innovative ST-360 framework specifically designed for 360-degree video analytics. This framework features a spatial-temporal filtering algorithm that optimizes both data transmission and computational workloads. Evaluation of the ST-360 framework on a unique dataset of 360-degree first-responders videos reveals that it yields accurate query results with a 50% reduction in end-to-end latency compared to state-of-the-art methods. 

The emergence of 360-video streaming systems has brought about new possibilities for immersive video experiences while requiring significantly higher bandwidth than traditional 2D video streaming. Viewport prediction is used to address this problem, but interesting storylines outside the viewport are ignored. To address this limitation, we present SAVG360, a novel viewport guidance system that utilizes global content information available on the server side to enhance streaming with the best saliency-captured storyline of 360-videos. The saliency analysis is performed offline on the media server with powerful GPU, and the saliency-aware guidance information is encoded and shared with clients through the Saliency-aware Guidance Descriptor. This enables the system to proactively guide users to switch between storylines of the video and allow users to follow or break guided storylines through a novel user interface. Additionally, we present a viewing mode prediction algorithms to enhance video delivery in SAVG360. Evaluation of user viewport traces in 360-videos demonstrate that SAVG360 outperforms existing tiled streaming solutions in terms of overall viewport prediction accuracy and the ability to stream high-quality 360 videos under bandwidth constraints. Furthermore, a user study highlights the advantages of our proactive guidance approach over predicting and streaming of where users look. 

360-degree video is becoming an integral part of our content consumption through both video on demand and live broadcast services. However, live broadcast is still challenging due to the huge network bandwidth cost if all 360-degree views are delivered to a large viewer population over diverse networks. In this paper, we present 360BroadView, a viewer management approach to viewport prediction in 360-degree video live broadcast. We make some highbandwidth network viewers be leading viewers to help the others (lagging viewers) predict viewports during 360-degree video viewing and save bandwidth. Our viewer management maintains the leading viewer population despite viewer churns during live broadcast, so that the system keeps functioning properly. Our evaluation shows that 360BroadView maintains the leading viewer population at a minimal yet necessary level for 97 percent of the time. 

360-degree video based virtual tours are becoming more and more popular due to travel costs and restrictions. Existing solutions leverage teleport, 3D modeling or image morphing, but none of them offers satisfactory immersion and scalability. In this paper, we propose a morphing based ultra-sparse 360-degree camera virtual tourism solution. It uses a novel bus tour mode to improve immersion; besides, it uses a series of strategies to improve feature matching such that morphing works well for ultra-sparse (15 m apart) cameras and the system can be deployed on a large scale. The experimental results show that our work results in remarkably better feature matching and synthesized views. 

Immersive virtual tours based on 360-degree cameras, showing famous outdoor scenery, are becoming more and more desirable due to travel costs, pandemics and other constraints. To feel immersive, a user must receive the view accurately corresponding to her position and orientation in the virtual space when she moves inside, and this requires cameras’ orientations to be known. Outdoor tour contexts have numerous, ultra-sparse cameras deployed across a wide area, making camera pose estimation challenging. As a result, pose estimation techniques like SLAM, which require mobile or dense cameras, are not applicable. In this paper we present a novel strategy called 360ViewPET, which automatically estimates the relative poses of two stationary, ultra-sparse (15 meters apart) 360-degree cameras using one equirectangular image taken by each camera. Our experiments show that it achieves accurate pose estimation, with a mean error as low as 0.9 degree