In this paper, we analyzed the accuracy and precision of AprilTag as a visual fiducial marker in detail. We have analyzed error propagation along two horizontal axes along with the effect of angular rotation about the vertical axis. We have identified that the angular rotation of the camera (yaw angle) about its vertical axis is the primary source of error that decreases the precision to the point where the marker system is not potentially viable for sub-decimeter precise tasks. Other factors are the distance and viewing angle of the camera from the AprilTag. Based on these observations, three improvement steps have been proposed. One is the trigonometric correction of the yaw angle to point the camera towards the center of the tag. Second, the use of a custom-built yaw-axis gimbal, which tracks the center of the tag in real-time. Third, we have presented for the first time a pose-indexed probabilistic sensor error model of the AprilTag using a Gaussian Processes based regression of experimental data, validated by particle filter tracking. Our proposed approach, which can be deployed with all three improvement steps, increases the system's overall accuracy and precision by manifolds with a slight trade-off with execution time over commonly available AprilTag library. These proposed improvements make AprilTag suitable to be used as precision localization systems for outdoor and indoor applications. provide adequate accuracy for tasks that demand sub-meter localization accuracies such as robot navigation, obstacle avoidance or structural inspection in confined environments. Some high-end GPS methodologies such as D-GPS and RKT-GPS have an accuracy of 0.1 meters or less but they are quite expensive and are hard to setup. In outdoor environments, the deployment of fiducial marker-based systems are also possible but they have limitations on operating distance and field-of-view.AprilTag is one of the most commonly used fiducial markers that can be used both indoors and outdoors for ground truth generation in 6-DOF, but with limitations [6]. We have precisely identified these limitations and have explained the source of these limitations with statistical error models. The proposed research has established that both distance and orientation of viewing camera from the target tag effects accuracy. However, uncorrected orientation uncertainty is a more significant source of accuracy degradation. AprilTag's accuracy is maximum when the viewing camera is pointed towards the center of the tag. Moreover, in the current implementation of the AprilTag localization system, this source of error is left unaddressed. As a result, the system suffers from a loss of performance, which is rectifiable. The proposed research has filled this gap (only for 2D) via an empirical analysis of the AprilTag system. Furthermore, a data-driven probabilistic sensor model has also been proposed, which works both in indoor and outdoor environments.In this paper, we have proposed techniques to overcome this limitation and to increase the accuracy even f...

Abstract-Social networking web sites, which allow users to create identities and link them to friends who have also created identities, are highly popular. Systems such as Facebook and MySpace utilize a traditional client-server approach to achieve this, which means that all identities and their social links (the entire social network) are stored and administered on central servers. Although this approach supports highly mobile user access -users can log-in from any computer -it also poses high dependence on predefined central server(s), which results in possible exploitation of private data.In this paper we present an alternative approach, based on gossip protocol, in which we use a completely decentralized peer-to-peer system to create and store the social network. Our system is self-administered and works in a highly transient environment of peer availability. We propose the design and implementation in Tribler of a distributed social networking system that is scalable and robust, allowing users to perform core social networking functions of establishing and removing social links without any requirement for centralized servers or administration.

The electrochemical performances of CoSn2 and Ni3Sn4 as potential anode materials in lithium‐ion batteries (LIBs) are investigated using varying thicknesses of an alumina layer deposited by the atomic layer deposition (ALD) technique. Rate capability results showed that at high current densities, Al2O3‐coated CoSn2 and Ni3Sn4 electrodes after 10‐ALD cycles outperformed uncoated materials. The charge capacities of coated CoSn2 and Ni3Sn4 electrodes are 571 and 134 mAh g−1, respectively, at a high current density of 5 A g−1, while the capacities of uncoated electrodes are 363 and 11 mAh g−1. When the current density is reduced to 1 A g−1, however, the cycling performances of Al2O3‐coated CoSn2 and Ni3Sn4 electrodes fade faster after almost 40 cycles than uncoated electrodes. The explanation is found in the composition of the solid‐electrolyte interface (SEI), which strongly depends on the current rate. Thus, X‐ray photoelectron spectroscopy analysis of SEI layers on coated samples cycles at a low current density of 0.1 Ag−1, revealed organic carbonates as major products, which probably have a low ionic conductivity. In contrast, the SEI of coated materials cycled at 5 Ag−1 consists mostly of mixed inorganic/organic fluorine‐rich Al‐F and C‐F species facilitating a higher ionic transport, which improves electrochemical performance.

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