Virtual Plane Research Articles

On Analytic Methods for 2.5-D Local Sound Field Synthesis Using Circular Distributions of Secondary Sources

Local sound field synthesis allows for synthesizing a given desired sound field inside a limited target region such that the field is free of considerable spatial aliasing artifacts. Spatial aliasing artifacts are a consequence of overlaps due to unavoidable repetitions of the space-spectral coefficients of the secondary source driving function. We analyze various conceivable analytic ways of restricting the bandwidth of the spatial spectrum of the driving function such that considerable overlapping is prevented: local spatial bandlimitation (A), spectral windowing (B), and local spatial bandlimitation plus spectral windowing (C). While solution B is computationally significantly more efficient than A and C, it provides only limited control over the spatial location around which the aliasing-free region evolves. Solutions A and C provide more flexibility and higher accuracy whereby both achieve largely identical results so that the spectral windowing after the local spatial bandlimitation may be skipped. We present a detailed analysis of the properties of the spatial aliasing artifacts arising in the synthesis of a virtual plane wave. We establish a procedure for predicting the maximum possible size of the aliasing-free target region depending on its location and on the propagation direction of the desired sound field. The results can help reducing regularization in numerical solutions as they represent physical limitations that can be considered in the choice of parameters.

KULLANIM ÖNCESİNDE SANAL GERÇEKLİK TEKNOLOJİLERİNİN DEĞERLENDİRİLMESİ İÇİN BİR KURAMSAL ÇERÇEVE: UYARLANMIŞ İLETİŞİM ORTAMLARI DOĞALLIĞI KURAMI TEMELİNDE BİR BİYOLOJİK EVRİMSEL YAKLAŞIM

The rapid development of information and communication technologies has opened a whole new realm of applications for these technologies. One such application is the development of virtual reality, which aspires to immerse the user within the system such that they feel more “present” within the portrayed virtual plane of existence than within their true reality. Many studies have developed a variety of approaches and methods on measuring immersion and presence in these systems, yet few have addressed the underlying technology for what it really is – namely communication technology – and evaluated the technology’s potential for immersion and presence before exposing the user to the virtual experience. Part of the issue lies in the difficulty in quantifying arguably subjective experiences such as immersion and presence. This study examines the existing literature on the definition and evaluation of immersion, presence, and virtual reality technologies, and aims to provide a theoretical framework through which virtual reality technology may be evaluated based on the human biological apparatus it appeals to. The framework is constructed on a modified version of the Media Naturalness Theory, which was selected as a basis due to the evolutionary support it provides in explaining our communication preferences. The framework may then be utilized to analyze prospective technologies for their potential to provide immersive experiences and incite presence in the users before any exposure or use has taken place, possibly providing further validity to any findings of post-exposure studies (such as with questionnaires so ubiquitous in the literature of the field).

The Influence of Human Body Orientation on Distance Judgments

People maintain larger distances to other peoples’ front than to their back. We investigated if humans also judge another person as closer when viewing their front than their back. Participants watched animated virtual characters (avatars) and moved a virtual plane toward their location after the avatar was removed. In Experiment 1, participants judged avatars, which were facing them as closer and made quicker estimates than to avatars looking away. In Experiment 2, avatars were rotated in 30 degree steps around the vertical axis. Observers judged avatars roughly facing them (i.e., looking max. 60 degrees away) as closer than avatars roughly looking away. No particular effect was observed for avatars directly facing and also gazing at the observer. We conclude that body orientation was sufficient to generate the asymmetry. Sensitivity of the orientation effect to gaze and to interpersonal distance would have suggested involvement of social processing, but this was not observed. We discuss social and lower-level processing as potential reasons for the effect.

Quantitative assessment of anatomical change using a virtual proton depth radiograph for adaptive head and neck proton therapy.

The aim of this work is to demonstrate the feasibility of using water‐equivalent thickness (WET) and virtual proton depth radiographs (PDRs) of intensity corrected cone‐beam computed tomography (CBCT) to detect anatomical change and patient setup error to trigger adaptive head and neck proton therapy. The planning CT (pCT) and linear accelerator (linac) equipped CBCTs acquired weekly during treatment of a head and neck patient were used in this study. Deformable image registration (DIR) was used to register each CBCT with the pCT and map Hounsfield units (HUs) from the planning CT (pCT) onto the daily CBCT. The deformed pCT is referred as the corrected CBCT (cCBCT). Two dimensional virtual lateral PDRs were generated using a ray‐tracing technique to project the cumulative WET from a virtual source through the cCBCT and the pCT onto a virtual plane. The PDRs were used to identify anatomic regions with large variations in the proton range between the cCBCT and pCT using a threshold of 3 mm relative difference of WET and 3 mm search radius criteria. The relationship between PDR differences and dose distribution is established. Due to weight change and tumor response during treatment, large variations in WETs were observed in the relative PDRs which corresponded spatially with an increase in the number of failing points within the GTV, especially in the pharynx area. Failing points were also evident near the posterior neck due to setup variations. Differences in PDRs correlated spatially to differences in the distal dose distribution in the beam's eye view. Virtual PDRs generated from volumetric data, such as pCTs or CBCTs, are potentially a useful quantitative tool in proton therapy. PDRs and WET analysis may be used to detect anatomical change from baseline during treatment and trigger further analysis in adaptive proton therapy.PACS number(s): 87.55‐x, 87.55.‐D, 87.57.Q‐

Imaging of sub-wavelength structures radiating coherently near microspheres

Using a two-dimensional model, we show that the optical images of a sub-wavelength object depend strongly on the excitation of its electromagnetic modes. There exist modes that enable the resolution of the object features smaller than the classical diffraction limit, in particular, due to the destructive interference. We propose to use such modes for super-resolution of resonant structures such as coupled cavities, metal dimers, or bowties. A dielectric microsphere in contact with the object forms its magnified image in a wide range of the virtual image plane positions. It is also suggested that the resonances may significantly affect the resolution quantification in recent experimental studies.

Piecewise-planar reconstruction using two views

The article describes a reconstruction pipeline that generates piecewise-planar models of man-made environments using two calibrated views. The 3D space is sampled by a set of virtual cut planes that intersect the baseline of the stereo rig and implicitly define possible pixel correspondences across views. The likelihood of these correspondences being true matches is measured using signal symmetry analysis [1], which enables to obtain profile contours of the 3D scene that become lines whenever the virtual cut planes intersect planar surfaces. The detection and estimation of these lines cuts is formulated as a global optimization problem over the symmetry matching cost, and pairs of reconstructed lines are used to generate plane hypotheses that serve as input to PEARL clustering [2]. The PEARL algorithm alternates between a discrete optimization step, which merges planar surface hypotheses and discards detections with poor support, and a continuous optimization step, which refines the plane poses taking into account surface slant. The pipeline outputs an accurate semi-dense Piecewise-Planar Reconstruction of the 3D scene. In addition, the input images can be segmented into piecewise-planar regions using a standard labeling formulation for assigning pixels to plane detections. Extensive experiments with both indoor and outdoor stereo pairs show significant improvements over state-of-the-art methods with respect to accuracy and robustness.

Heterogeneous Multi-View Information Fusion: Review of 3-D Reconstruction Methods and a New Registration with Uncertainty Modeling

We consider a multisensor network fusion framework for 3-D data registration using inertial planes, the underlying geometric relations, and transformation model uncertainties. We present a comprehensive review of 3-D reconstruction methods and registration techniques in terms of the underlying geometric relations and associated uncertainties in the registered images. The 3-D data registration and the scene reconstruction task using a set of multiview images are an essential goal of structure-from-motion algorithms that still remains challenging for many applications, such as surveillance, human motion and behavior modeling, virtual-reality, smart-rooms, health-care, teleconferencing, games, human–robot interaction, medical imaging, and scene understanding. We propose a framework to incorporate measurement uncertainties in the registered imagery, which is a critical issue to ensure the robustness of these applications but is often not addressed. In our test bed environment, a network of sensors is used where each physical node consists of a coupled camera and associated inertial sensor (IS)/inertial measurement unit. Each camera-IS node can be considered as a hybrid sensor or fusion-based virtual camera. The 3-D scene information is registered onto a set of virtual planes defined by the IS. The virtual registrations are based on using the homography calculated from 3-D orientation data provided by the IS. The uncertainty associated with each 3-D point projected onto the virtual planes is modeled using statistical geometry methods. Experimental results demonstrate the feasibility and effectiveness of the proposed approach for multiview reconstruction with sensor fusion.

Planar Path Following of Underwater Snake Robots in the Presence of Ocean Currents

This letter presents a control system that enables an underwater snake robot to converge towards and follow a straight path in the presence of constant irrotational ocean currents. The robot is assumed to be neutrally buoyant, fully submerged and moving in a virtual plane with a sinusoidal gait and limited link angles. The proposed control approach uses a heading controller that exponentially stabilises the heading of the robot towards the desired heading, which is obtained by an integral line-of-sight guidance law. Uniform semiglobal exponential stability of the control system is formally proved using cascaded systems and Lyapunov theory. Simulations are presented that illustrate and validate the theoretical results.

Analysis of superiorly projecting anterior communicating artery aneurysms: anatomy, techniques, and outcome. A proposed classification system.

Superiorly projecting (SP) anterior communicating artery (AComA) aneurysms are typically described as a homogenous group. Clinically and microsurgically, these aneurysms vary in multiple important characteristics. We propose a microsurgical classification system for these complex aneurysms and review its implications regarding presentation, microsurgical techniques, and outcome. This retrospective analysis reviews patients undergoing clipping of SP AComA aneurysms (2005-2013). The classification system is based on the virtual plane created by the A2 segments and its relationship to the aneurysm. Aneurysm type was assessed by intraoperative images and videos. Type 1 is defined by bisection of the dome by the virtual plane. Type 2 is defined by dome projection posterior to this plane. Sagittal rotation of the plane defines type 3. We analyzed clinical presentation, morphology, angiographic characteristics, operative technique, and outcome relative to the classification types. There were 44 SP AComA aneurysms. 3D angiographic images predicted classification type in 83%. Type 1 presented more often with SAH (95.5%, p = 0.0046). There was no statistically significant difference between the types regarding patient demographics or aneurysm characteristics. In type 2, fenestrated clips were used frequently (87.5% p= 0.0016), and there was higher rate of intraoperative rupture (37.5%). Although there was no statistically significant difference between the types in respect to HH grade upon presentation, patients with type 2 aneurysms experienced higher rates of poor GOS (50%). The proposed classification system for SP AComA aneurysms has implications regarding surgical planning, micro-dissection, clipping, and outcome. Type 2 aneurysms carry significant surgical risk.

State transformation-based dynamic visual servoing for an unmanned aerial vehicle

abstractIn this paper, we propose a visual servoing control for a quadrotor unmanned aerial vehicle (UAV) which is based on a state transformation technique. The UAV is equipped with a single downwards facing camera, and the motion control objective is the regulation of relative displacement and yaw to a stationary visual target located on the ground. The state transformation is defined by a system of partial differential equations (PDEs) which eliminate roll and pitch rate dependence in the transformed image feature kinematics. A method for computing the general solutions of these PDEs is given, and we show a particular solution reduces to an established virtual camera approach. We treat point and line cases and introduce image moment features defined in the virtual camera image plane. Robustness of the control design is improved by accounting for attitude measurement bias, and uncertainty in thrust gain, mass, and image feature depth. The asymptotic stability of the closed-loop is proven. The method is based on a simple proportional-integral-derivative (PID) structure which can be readily implemented on-board. Experimental results show improved performance relative to previous work.

Acervo com Realidade Mista: projeto Talking Statues e perspectivas museais, no ambiente urbano.

A utilizacao da tecnologia de Realidade Mista, no campo da arte e da museologia, e cada vez mais frequente. Nas duas ultimas decadas, esse tipo de tecnologia viabilizou o desdobramento espacial e temporal, de modo consciente, indissociando o plano fisico do virtual. O projeto Talking Statues (2014), permite analisar o modo como a Realidade Mista pode ser aplicada no espaco urbano, sobretudo, na construcao de um acervo interativo, alem do territorio institucional. A acao nao esta livre dos interesses e poderes, porem, reflete um novo direcionamento das tensoes quanto ao acervo e ao museu, propriamente ditos. Este artigo, no campo da Historia e Teoria da Arte Contemporânea, discute essas novas tensoes e direcionamentos, a partir do projeto artistico e interativo, realizado em Londres. DOI: http://dx.doi.org/10.35700/ca.2015.ano2n3.p34-43.1830

Acervo com Realidade Mista: projeto Talking Statues e perspectivas museais, no ambiente urbano

The use of Mixed Reality technology in the field of art and museology, is increasingly common. In the last two decades, this type of technology review the spatial and temporal concept, consciously, between the physical and virtual plane, in a continuous connected condition. The project Talking Statues (2014), allows us to analyze how the Mixed Reality can be applied in urban areas, especially in the construction of an interactive collection, beyond the institutional territory. The action is not free from interests and tensions, however, reflects a new direction of the tensions regarding the collection and the museum itself. This article, in the field of History and Theory of Contemporary Art, discusses these new stresses and directions, from the artistic and interactive design, held in London.

Noncoplanar verification: a feasibility study using Philips' Pinnacle3 treatment planning system.

Noncoplanar fields are normally used to improve the dose conformity of the target while sparing organs at risk. One of the methods to verify the dose distribution from the noncoplanar fields is by comparing their planar dose distributions from the treatment planning system (TPS) and the measured ones; for example, using film or electronic portal imaging devices (EPID). The planar dose distributions of the measurement tools, that are normally perpendicular to the central axis of the beam, can be calculated by creating special structures to mimic them in the TPS. With TPS commercially available today, however, it is not easy to create these special structures, especially in the noncoplanar configuration. For this work, we have written in‐house scripts in the Pinnacle3 TPS that can create the structures and define them as virtual planes. These virtual planes can be generated for any arbitrary gantry and couch angles, as well as source to planar distance, so that the planar dose maps at these planes can be computed. Two independent quality assurance (QA) tools were used to validate the planar dose distributions computed using the scripts for three open fields and one IMRT field at several different couch angles. The absolute planar dose patterns measured by the QA tools for all fields at all couch angles were found to be in good agreement, more than 95% (gamma criteria 3% delta dose and 3 mm distance to agreement), with the calculated ones by TPS. The results of this feasibility study can be valuable either for pretreatment dose verification or for in vivo dosimetry that directly implements the planar dose distributions from the TPS, particularly for the noncoplanar fields.PACS numbers: 87.55.de, 87.55.Qr, 87.56.Fc

Reference plane correction of online grating projection-based 3D measurement

In the process of grating stripe reflection-based three-dimensional measurement, selection of the reference influences the precision much. In this paper, a correction method of the reference for dynamic measurement based on the virtual reference plane and the stripe processing is proposed. Before dynamic measurement, a checkerboard image is projected onto the mirror that is placed on the object, and the virtual image is set as the virtual reference plane. According to the correspondent relationship between the points on the virtual reference plane and those in the reference coded stripes on the object surface, the reference phase distribution in the vertical direction can be figured out, and thus, the remeasurement of reference plane could be avoided. In the process of dynamic measurement, in order to avoid the influence of the fringe direction change caused by the vibrations, we process the stripes, rotating the direction to that of the stripes on the virtual reference, and thus, reduce the error of the vibration.

Virtual machine-based simulation platform for mobile ad-hoc network-based cyber infrastructure

In modeling and simulating complex systems, such as mobile ad-hoc networks (MANETs), in defense communications, it is a major challenge to reconcile multiple important considerations: the rapidity of unavoidable changes to the software (network layers and applications), the difficulty of modeling the critical, implementation-dependent behavioral effects, the need to sustain larger scale scenarios, and the desire for faster simulations. Here we present our approach in successfully reconciling them using a virtual time-synchronized virtual machine (VM)-based parallel execution framework that accurately lifts both the devices, as well as the network communications, to a virtual time plane while retaining full fidelity. At the core of our framework is a scheduling engine that operates at the level of a hypervisor scheduler, offering a unique ability to execute multi-core guest nodes over multi-core host nodes in an accurate, virtual time-synchronized manner. In contrast to other related approaches that suffer from either speed or accuracy issues, our framework provides MANET node-wise scalability, high fidelity of software behaviors, and time-ordering accuracy. The design and development of this framework is presented, and an actual implementation based on the widely used Xen hypervisor system is described. Benchmarks with synthetic and actual applications are used to identify the benefits of our approach. The time inaccuracy of traditional emulation methods is demonstrated, in comparison with the accurate execution of our framework verified by theoretically correct results expected from analytical models of the same scenarios. In the largest high-fidelity tests, we are able to perform virtual time-synchronized simulation of 64-node VM-based full-stack, actual software behaviors of MANETs containing a mix of static and mobile (unmanned airborne vehicle) nodes, hosted on a 32-core host, with full fidelity of unmodified ad-hoc routing protocols, unmodified application executables, and user-controllable physical layer effects, including inter-device wireless signal strength, reachability, and connectivity.

Modeling face routing in unit disk graphs

The features of using unit disk graphs in modeling face routing are described. The basic geometricalproperties of the interaction of nodes in the unit disk graphs are defined in this article. An algorithmfor calculating the path of packet delivery, which is based on the method of calculating the virtualpath in the virtual plane graphs is proposed

Reflector antenna analysis method using Poynting vector tracing between virtual apertures

In this study, a highly efficient calculation method for analysing electrically large reflector antennas is presented. This method utilises fast Fourier transform enhanced direct integration to calculate beam propagation between parallel virtual apertures, and a novel Poynting vector tracing technique is introduced to treat wave reflections by arbitrary curved surface. Two virtual apertures are set perpendicular to the incident and reflected optical paths. As the centres of the virtual aperture planes coincide with the reflector surface, it makes the ray-tracing paths between the virtual apertures along with the reflector as short as possible. Owing to these innovative treatments, this method offers a high calculation accuracy comparable with classic physical optics (PO), but with much higher efficiency. By performing numerical comparisons with method of moments, PO algorithm implemented with commercial software FEKO and general reflector antenna software package, the advantages of the proposed method are presented in this study. The method proves to be applicable for the analysis of electrically large reflector antennas.

Shaft Diameter Measurement Using Structured Light Vision.

A method for measuring shaft diameters is presented using structured light vision measurement. After calibrating a model of the structured light measurement, a virtual plane is established perpendicular to the measured shaft axis and the image of the light stripe on the shaft is projected to the virtual plane. On the virtual plane, the center of the measured shaft is determined by fitting the projected image under the geometrical constraints of the light stripe, and the shaft diameter is measured by the determined center and the projected image. Experiments evaluated the measuring accuracy of the method and the effects of some factors on the measurement are analyzed.

Mitral valve analysis adding a virtual semi-transparent annulus plane for detection of prolapsing segments.

BackgroundWe hypothesized that a novel three-dimensional virtual semi-transparent annulus plane (3D VSAP) presented on a holographic screen can be used to visualize the prolapsing tissue in degenerative mitral valve disease and furthermore, provide us with geometrical data of the mitral valve apparatus. Phantom and patient studies were designed to demonstrate the feasibility of creating a semi-automatic, semi-transparent mitral annulus plane visualized on a holographic display.MethodsTen pipe cleaners mimicking the mitral annulus with different shapes and three types of annuloplasty rings served as phantoms. We obtained 3D transoesophageal examination of the phantoms in a special designed box filled with water. Recordings were converted to the holographic display and a 3D VSAP was created. The ratio of the major and minor axes as well as the non-planar angles were calculated and compared with direct measures of the phantoms. Forty patients with degenerative mitral valve disease were then analyzed with 3D transthoracic echocardiography (TTE) and a 3D VSAP was created on the holographic display. A total of 240 segments were analyzed by two independent observers, one echo expert (observer I), and the other novice with limited echo experience (observer II). The two observers created the 3D VSAP in each patient before suggesting the valve pathology.ResultsThe major/minor axes ratio and non-planar angles by 3D VSAP correlated with direct measurements by r = 0.65, p < 0.02 and r = 0.99, p < 0.0001, respectively. The sensitivity and specificity of the 3D VSAP method in patients was 81 and 97 %, respectively (observer I) and for observer II 77 and 96 %, respectively. The accuracy and precisions were 93.9 and 89.4 %, respectively (observer I), 92.3 and 85.1 % (observer II). Mitral valve analysis adding a 3D VSAP was feasible with high accuracy and precision, providing a quick and less subjective method for diagnosing mitral valve prolapse. This novel method may improve preoperative diagnostics and may relieve a better understanding of the pathophysiology of mitral valve disease. Thus, based on the specific findings in each patient, a tailored surgical repair can be planned and hopefully enhance long-term repair patency in the future.

Reconstruction of transient vibration and sound radiation of an impacted plate using time domain plane wave superposition method

Time domain plane wave superposition method is extended to reconstruct the transient pressure field radiated by an impacted plate and the normal acceleration of the plate. In the extended method, the pressure measured on the hologram plane is expressed as a superposition of time convolutions between the time–wavenumber normal acceleration spectrum on a virtual source plane and the time domain propagation kernel relating the pressure on the hologram plane to the normal acceleration spectrum on the virtual source plane. By performing an inverse operation, the normal acceleration spectrum on the virtual source plane can be obtained by an iterative solving process, and then taken as the input to reconstruct the whole pressure field and the normal acceleration of the plate. An experiment of a clamped rectangular steel plate impacted by a steel ball is presented. The experimental results demonstrate that the extended method is effective in visualizing the transient vibration and sound radiation of an impacted plate in both time and space domains, thus providing the important information for overall understanding the vibration and sound radiation of the plate.