scholarly journals Visual Collaboration Leader-Follower UAV-Formation for Indoor Exploration

2022 ◽  
Vol 8 ◽  
Author(s):  
Nikolaos Evangeliou ◽  
Dimitris Chaikalis ◽  
Athanasios Tsoukalas ◽  
Anthony Tzes
Keyword(s):  
Data Exchange ◽  
Experimental Studies ◽  
Field Of View ◽  
Detection Error ◽  
Data Packets ◽  
Communication Latency ◽  
Position Detection ◽  
Rf Communication ◽  
Constant Distance ◽  
Relative Pose

UAVs operating in a leader-follower formation demand the knowledge of the relative pose between the collaborating members. This necessitates the RF-communication of this information which increases the communication latency and can easily result in lost data packets. In this work, rather than relying on this autopilot data exchange, a visual scheme using passive markers is presented. Each formation-member carries passive markers in a RhOct configuration. These markers are visually detected and the relative pose of the members is on-board determined, thus eliminating the need for RF-communication. A reference path is then evaluated for each follower that tracks the leader and maintains a constant distance between the formation-members. Experimental studies show a mean position detection error (5 × 5 × 10cm) or less than 0.0031% of the available workspace [0.5 up to 5m, 50.43° × 38.75° Field of View (FoV)]. The efficiency of the suggested scheme against varying delays are examined in these studies, where it is shown that a delay up to 1.25s can be tolerated for the follower to track the leader as long as the latter one remains within its FoV.

scholarly journals The interference immunity of decameter circuit with spatial interference compensation

2021 ◽  
pp. 109-114
Author(s):  
И.М. Орощук ◽  
В.В. Клоков
Keyword(s):  
Data Exchange ◽  
Channel Model ◽  
World Ocean ◽  
Experimental Studies ◽  
Interference Immunity ◽  
Interference Compensation ◽  
Spatial Method ◽  
Ionospheric Channel ◽  
Spatial Interference ◽  
Correlation Properties

В статье представлена оценка помехоустойчивости декаметрового канала связи, использующего пространственный метод компенсации естественных помех. Метод компенсации базируется на результаты экспериментальных исследований пространственно-корреляционных свойств сигналов и естественных помех декаметрового диапазона. Для реализации метода используется цифровая антенная решетка с пространственно-корреляционным методом обработки сигналов. Также в канале использована гауссовая амплитудная модуляция, формирующая шумоподобный сигнал с расширенной базой. Оценка помехоустойчивости построена на модели ионосферного канала с релеевскими замираниями с учетом пространственно-корреляционных свойств сигналов и естественных помех. Анализ проведенных исследований показал возможность компенсации помех за счет роста антенных элементов в антенной решетке, которая, как следствие, позволит повысить помехоустойчивость ионосферного декаметрового канала связи при низких отношениях уровней сигнал/шум на входе приемного тракта. Возможность обеспечения высокой помехоустойчивости в ионосферных декаметровых каналах позволит использовать новые виды связи для обмена данными в судами и кораблями ВМФ в пределах акваторий Мирового океана. The interference immunity assessment of the decameter circuit using a spatial method of natural interference compensation is presented. The compensation method is based on experimental studies results of spatial and correlation properties of decameter range signals and natural interference. For the method realization the digital array with a spatially-correlation signals processing method is used. Also in the channel the Gaussian amplitude modulation forming a noise-shaped signal with extended base is used. The interference immunity assessment is based on the ionospheric channel model with the Rayleigh fadings taking into account signals and natural interference spatially-correlation properties. The simulation findings showed the interference compensation possibility due to increase in antenna array elements which, as a result, will allow to increase the interference immunity of ionospheric decameter circuit at the low levels of signal/noise ratio in the reception path entrance. The possibility of ensuring high interference immunity in ionospheric decameter circuits will allow to use new communication types for data exchange with NAVY battleships and vessels within the World Ocean water areas.

scholarly journals Recording Natural Head Position Using Cone Beam Computerized Tomography

Sensors ◽  
2021 ◽  
Vol 21 (24) ◽  
pp. 8189
Author(s):  
Tai-Chiu Hsung ◽  
Wai-Kan Yeung ◽  
Wing-Shan Choi ◽  
Wai-Kuen Luk ◽  
Yi-Yung Cheng ◽  
...  
Keyword(s):  
Computerized Tomography ◽  
Head Position ◽  
Field Of View ◽  
Cone Beam ◽  
Detection Error ◽  
Cone Beam Computerized Tomography ◽  
The Subject ◽  
And Performance ◽  
Phantom Head ◽  
Additional Hardware

The purpose of this study was to develop a technique to record the natural head position (NHP) of a subject using the scout images of cone beam computerized tomography (CBCT) scans. The first step was to align a hanging mirror with the vertical (XY) plane of the CBCT field-of-view (FOV) volume. Then, two scout CBCT images, at frontal and at sagittal planes, were taken when the subject exhibited a NHP. A normal CBCT scan on the subject was then taken separately. These scout images were used to correct the orientation of the normal CBCT scan. A phantom head was used for validation and performance analysis of the proposed method. It was found that the orientation detection error was within 0.88°. This enables easy and economic NHP recording for CBCT without additional hardware.

Blind position detection for large field-of-view scattering imaging

2020 ◽  
Vol 8 (6) ◽  
pp. 920 ◽  
Author(s):  
Xiaoyu Wang ◽  
Xin Jin ◽  
Junqi Li
Keyword(s):  
Field Of View ◽  
Large Field ◽  
Position Detection

scholarly journals Multi-view point cloud fusion for LiDAR based cooperative environment detection

2015 ◽  
Vol 13 ◽  
pp. 209-215
Author(s):  
B. Jaehn ◽  
P. Lindner ◽  
G. Wanielik
Keyword(s):  
Pose Estimation ◽  
Urban Areas ◽  
Ground Truth ◽  
Field Of View ◽  
Automated Driving ◽  
Ground Truth Data ◽  
Registration Method ◽  
Relative Pose ◽  
Heading Estimation ◽  
Environment Detection

Abstract. A key component for automated driving is 360° environment detection. The recognition capabilities of modern sensors are always limited to their direct field of view. In urban areas a lot of objects occlude important areas of interest. The information captured by another sensor from another perspective could solve such occluded situations. Furthermore, the capabilities to detect and classify various objects in the surrounding can be improved by taking multiple views into account. In order to combine the data of two sensors into one coordinate system, a rigid transformation matrix has to be derived. The accuracy of modern e.g. satellite based relative pose estimation systems is not sufficient to guarantee a suitable alignment. Therefore, a registration based approach is used in this work which aligns the captured environment data of two sensors from different positions. Thus their relative pose estimation obtained by traditional methods is improved and the data can be fused. To support this we present an approach which utilizes the uncertainty information of modern tracking systems to determine the possible field of view of the other sensor. Furthermore, it is estimated which parts of the captured data is directly visible to both, taking occlusion and shadowing effects into account. Afterwards a registration method, based on the iterative closest point (ICP) algorithm, is applied to that data in order to get an accurate alignment. The contribution of the presented approch to the achievable accuracy is shown with the help of ground truth data from a LiDAR simulation within a 3-D crossroad model. Results show that a two dimensional position and heading estimation is sufficient to initialize a successful 3-D registration process. Furthermore it is shown which initial spatial alignment is necessary to obtain suitable registration results.

scholarly journals Artifacts related to cone beam computed tomography technology (CBCT) and their significance for clinicians: illustrated review of medical literature.

NEMESIS ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 1-29
Author(s):  
Raphael Olszewski
Keyword(s):  
Computed Tomography ◽  
Dental Implants ◽  
Cone Beam Computed Tomography ◽  
Experimental Studies ◽  
Field Of View ◽  
Cone Beam ◽  
Beam Hardening ◽  
Exclusion Criteria ◽  
Ring Artifact ◽  
Pubmed Database

Objective: to explain the meaning and to illustrate technical artifacts (aliasing as well as the ring artifact) and beam hardening (metal artifact) that can be present in the dentomaxillofacial cone beam computed tomography (CBCT), and to check the accessibility of free illustrations of these artifacts in medical publications. Material and methods: One observer applied five search equations using database PubMed. The exclusion criteria were: experimental studies, animal studies, studies not related to dentomaxillofacial area, and articles with closed access. There was no time limit for the search of articles. We limited our search to English and French language. Results: Only 3 articles out of 434 publications were retained after application of inclusion/exclusion criteria. In these articles only 4 annotated figures were freely accessible in medical publications from PubMed. In this paper we presented examples of aliasing, ring artifact, and beam artifacts from I-CAT, Carestream 9000 3D (Kodak), and Planmeca Promax 3D Mid CBCT. The intensity of beam hardening artifact varies from major degradation of image (i.e., subperiosteal implants, bridges, crowns, dental implants, and orthodontic fix appliances), through mean degradation (screws securing titanium mesh, head of mini-implant) to no beam hardening on metallic devices (orthodontic anchorage, orthodontic contention wire) or on dense objects (endodontic treatments, impression materials, Lego box). Some beam hardening artifacts arising from nasal piercing, hairs, or hearing aid device may be present on the image but they will not disturb the evaluation of the field of view. Conclusions: reduction of aliasing artifact is related with the improvement of detectors quality. The presence of ring artifact means that CBCT device has lost its calibration. The field of view (FOV) needs to be reduce in order to avoid scanning regions susceptible to beam hardening (e.g., metallic restorations, dental implants). Finally, the accessibility to open knowledge on technique -related CBCT artifacts seems extremely limited when searching at PubMed database.

scholarly journals The structure of turbulent flow behind the NACA 0012 airfoil at high angles of attack and low Reynolds number

2021 ◽  
Vol 345 ◽  
pp. 00034
Author(s):  
Vitalii Yanovych ◽  
Daniel Duda ◽  
Václav Uruba ◽  
Pavlo Kosiak
Keyword(s):  
Reynolds Number ◽  
Standard Deviation ◽  
Experimental Studies ◽  
Turbulent Structure ◽  
Pressure System ◽  
Micro Scale ◽  
Measuring Section ◽  
Constant Distance ◽  
Naca 0012 ◽  
High Angles Of Attack

This paper shows the results of a study of the turbulent structure behind the NACA 0012 airfoil. During the experiment, the flow velocity was 20 m·s−1. That corresponds the Reynolds number 1.3·105. The point behind the trailing edge was chosen for experimental studies. Measurements were performed at six angles of attack α = 0°, 15°, 30°, 45°, 60°, 75° and various cases of positioning the measuring section. Namely at a constant crosssection and a constant distance behind the airfoil. The NetScanner pressure system and hot-wire technique were used for experimental studies. The obtained data allowed us to investigate the wake topology. The average velocity and standard deviation distributions are clearly grouped depending on the angle of attack. Thus, flowing around the airfoil is better up to α ≤15°. Distributions by power density and dissipation spectra also have a similar grouping tendency. Finally, we investigated the turbulent structure according to the research program. We found that at α ≥45°, depending on the measurement case, there is a clear difference in the distribution of standard deviation, Eulerian length scale, Taylor micro-scale, and Reynolds number based on the Taylor micro-scale. The obtained values at the constant distance, in contrast to the constant cross-section, are reduced.

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