1,721,046 research outputs found
A game-theoretic approach to matching and robust inlier selection
Full text linkIn questa tesi la nostra attenzione è rivolta alla classe di problemi di matching dove qualche funzione di compatibilità e definibile su un insieme di due o più coppie corrispondenti. Nello specifico proponiamo un approccio flessibile che sfrutta la teoria dei giochi per permettere l'evoluzione di un'iniziale popolazione di ipotesi verso uno stato evolutivamente stabile dove un ristretto insieme di corrispondenze altamente compatibili è riuscito a sopravvivere. La motivazione che spinge ad adottare tale approccio è duplice. Infatti da un punto di vista teorico è possibile dimostrare che in molte formulazioni di problemi gli stati evolutivamente stabili o gli equilibri di Nash corrispondono a configurazioni desiderabili della soluzione, quali ad esempio isomorfismi massimali o allineamenti ottimali di superfici. Inoltre sono disponibili in letteratura molti algoritmi efficienti per guidare il processo evolutivo e, come mostreremo con un'estensiva copertura sperimentale, persino le dinamiche più semplici permettono di condurre la popolazione iniziale verso un match ottimale. Applicando il nostro framework a diverse tipologie di scenario mostreremo la sua efficacia sia in contesti di matching pairwise, sia coinvolgendo compatibilità di ordine superiore
Semi-supervised Segmentation of 3D Surfaces Using a Weighted Graph Representation
Full text linkA wide range of cheap and simple to use 3D scanning devices has recently been introduced in the market. These tools are no longer addressed to research labs and highly skilled professionals. By converse, they are mostly designed to allow inexperienced users to easily and independently acquire surfaces and whole objects. In this scenario, the demand for automatic or semi-automatic algorithms for 3D data processing is increasing. Specifically, in this paper we concentrate on the segmentation task applied to the acquired surfaces. Such a problem is well known to be ill-defined both for 2D images and 3D objects. In fact, even with a perfect understanding of the scene, many different and incompatible semantic or syntactic segmentations can exist together. For this reasons, we refrain from any attempt to offer an automatic solution. Instead we introduce a semi-supervised procedure that exploits an initial set of seeds selected by the user. In our framework segmentation happens by iteratively visiting a weighted graph representation of the surface starting from the supplied seeds. The assignment of each element is driven by a greedy approach that accounts for the curvature between adjacent triangles. The proposed technique does not require to perform edge detection or to fit parametrized surfaces and its implementation is very straightforward. Still, despite its simplicity, tests made on scanned 3D objects show its effectiveness and easiness of use. © 2011 Springer-Verlag Berlin Heidelberg
Sandboxed interaction for casual users in shared spaces
No full textA simple and natural interaction is considered the most important feature of an interface for multiple impromptu users in public spaces. Intuitiveness and forthright feedback are key factors to enable a steep learning curve for untrained users that need to grasp the interaction model in a short time span. The lack of proper constraints, designed to restrict and guide the user actions, might hinder such intuitiveness, mainly when the number of users grows or their behavior is exceedingly unrestrained. In this paper we introduce the idea of sandboxed interaction, a general concept that groups many flavors of physical and software-based measures aiming at guaranteeing a smooth and fitting interaction. To this end, we propose different types of sandboxes, suitable to handle different kind of interaction problems, and discuss a case study where several sandboxing measures have been put into use and evaluated within a real-world application scenario. © 2014 ACM
Quality and Impact Monitoring for Local eGovernment Services
Full text linkPurpose – The purpose of this paper is to introduce a layered, comprehensive model of quality of service (QoS) for local eGovernment, and discuss its feasibility on a regional eGovernment case study. The eGovernment online services are becoming a key infrastructure for advanced countries. They allow significant efficiency gains in different sectors of society, offering benefits for individual citizens and for the community as a whole. The deployment of online services alone is not sufficient in order to qualify an eGovernment strategy. The intrinsic and perceived quality of services offered, as well as the actual impact of new functionalities, should be properly measured and taken into account.
Design/methodology/approach – This paper presents an applied research study for a quality-focused evolution of a service-oriented architecture for local eGovernment portals. This investigation was based on three main layers: the perceived quality and effective impact of services (G2C layer), the effectiveness of the deployed processes (WFM layer) and finally, the system-level efficiency (G2G layer).
Findings – The measurement of quality with respect to eGovernment services is a complex task which requires appropriate tools to tackle the different aspects of the problem. Specifically, active and passive tools (respectively surveys and usage analysis) should be used to evaluate the quality perceived by the users as well as the utility of the service itself. The efficiency of the back office workflow must be estimated measuring statistical and dynamical indicators. Finally, technical measures should be used to monitor the responsiveness and scalability of software implementations and deployment systems.
Social implications – A better knowledge regarding (e-)Government service delivery processes, their QoS and their impact on the society can empower both citizens and local administrators, and can help them to better improve the effectiveness of local government.
Originality/value – The multi-layered quality measurement architecture proposed in this paper offers local governments the capability to systematically monitor and analyse the quality of their online services. The business process management technologies allow citizens to get a better knowledge of the service delivery processes; the QoS measurements allow to improve control on them; and the eGovernment Intelligence model allows to better quantify their actual social impact
Sampling Relevant Points for Surface Registration
Full text linkSurface registration is a fundamental step in the reconstruction of three-dimensional objects. This is typically a two-step process where an initial coarse motion estimation is followed by a refinement step that almost invariably is some variant of Iterative Closest Point (ICP), which iteratively minimizes a distance function measured between pairs of selected neighboring points. The selection of relevant points on one surface to match against points on the other surface is an important issue in any efficient implementation of ICP, with strong implications both on the convergence speed and on the quality of the final alignment. This is due to the fact that typically on a surface there are a lot of low-curvature points that scarcely constrain the rigid transformation and an order of magnitude less descriptive points that are more relevant for finding the correct alignment. This results in a tendency of surfaces to "overfit" noise on low-curvature areas sliding away from the correct alignment. In this paper we propose a novel relevant-point sampling approach for ICP based on the idea that points in an area of great change constrain the transformation more and thus should be sampled with higher frequency. Experimental evaluations confront the alignment accuracy obtained with the proposed approach with those obtained with the commonly adopted uniform subsampling and normal-space sampling strategies. © 2011 IEEE
Imposing Semi-Local Geometric Constraints for Accurate Correspondences Selection in Structure from Motion: A Game-Theoretic Perspective
Full text linkMost Structure from Motion pipelines are based on the iterative refinement of an initial batch of feature correspondences. Typically this is performed by selecting a set of match candidates based on their photometric similarity; an initial estimate of camera intrinsic and extrinsic parameters is then computed by minimizing the reprojection error. Finally, outliers in the initial correspondences are filtered by enforcing some global geometric property such as the epipolar constraint. In the literature many different approaches have been proposed to deal with each of these three steps, but almost invariably they separate the first inlier selection step, which is based only on local image properties, from the enforcement of global geometric consistency. Unfortunately, these two steps are not independent since outliers can lead to inaccurate parameter estimation or even prevent convergence, leading to the well known sensitivity of all filtering approaches to the number of outliers, especially in the presence of structured noise, which can arise, for example, when the images present several repeated patterns. In this paper we introduce a novel stereo correspondence selection scheme that casts the problem into a Game-Theoretic framework in order to guide the inlier selection towards a consistent subset of correspondences. This is done by enforcing geometric constraints that do not depend on full knowledge of the motion parameters but rather on some semi-local property that can be estimated from the local appearance of the image features. The practical effectiveness of the proposed approach is confirmed by an extensive set of experiments and comparisons with state-of-the-art techniques
Phase-based spatio-temporal interpolation for accurate 3D localization in camera networks
No full textMany computer vision applications that exploit a network of independent cameras strongly depend on an accurate synchronization between them. This is indeed the case for 3D tracking. In fact, even if the calibration of the intrinsic and extrinsic parameters of each camera is flawless, inaccurate synchronization would still result in an impaired triangulation between incoherent projective images of the observed features. In many setups, synchronization can be guaranteed with specialized hardware supporting dedicated trigger control lines, however this becomes more difficult when dealing with a (possibly dynamic) network of distributed cameras communicating through wireless channels. With this paper we introduce an end-to-end solution to the problem, including a very simple hardware design for an easy to track device and a practical method that exploits its intrinsic properties for obtaining precise synchronization among an arbitrary number of cameras. Furthermore we propose a simple interpolation schema that can deal naturally with shots captured at different times. Our approach is highly scalable, since it does not require any kind of direct communication or synchronization between cameras. Moreover, new cameras can be added at any time without requiring any additional configuration. In order to test our method we built a specially crafted setup that we used to perform an exhaustive set of experiments
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