Browsing by Subject "Visibility"
Now showing 1 - 11 of 11
Results Per Page
Sort Options
Item Open Access An approximation algorithm for computing the visibility region of a point on a terrain and visibility testing(IEEE, 2014-01) Alipour, S.; Ghodsi, M.; Güdükbay, Uğur; Golkari, M.Given a terrain and a query point p on or above it, we want to count the number of triangles of terrain that are visible from p. We present an approximation algorithm to solve this problem. We implement the algorithm and then we run it on the real data sets. The experimental results show that our approximation solution is very close to the real solution and compare to the other similar works, the running time of our algorithm is better than their algorithm. The analysis of time complexity of algorithm is also presented. Also, we consider visibility testing problem, where the goal is to test whether p and a given triangle of train are visible or not. We propose an algorithm for this problem and show that the average running time of this algorithm will be the same as running time of the case where we want to test the visibility between two query point p and q.Item Open Access Cortical processes underlying attentional modulations of dynamic vision(Bilkent University, 2022-09) Çatak, Esra NurVisual attention is one of the most fundamental cognitive functions guiding and influencing a various number of processes. However, how different neural mechanisms are modulated by selective attention to process information is still subject to debate. Utilizing electroencephalography (EEG), the current thesis focused on understanding the time course of visual information processing and its neural underpinnings with paradigms that operate in different attentional modes, such as visual masking, attentional load, and transparent motion design. First, we aimed to understand the role of spatial attention in information processing and its possible interactions with metacontrast masking mechanisms. The behavioral results revealed an interaction effect that suggests differential effects of spatial attention on metacontrast masking. The following EEG analyses revealed significant activation due to masking and attentional load on early negative components located over occipital and parieto-occipital scalp sites, followed by a late positive component centered over centro-parietal electrodes. These findings suggest that the effect of spatial attention may have distinct characteristics at different stages of sensory and perceptual processing regarding its relationship with metacontrast masking. Secondly, by employing a novel variant of transparent motion design with color and motion swapping, we aimed to isolate the object-based cueing effect from a possible feature-based explanation in both psychophysical measures and neural activities. Our results demonstrate that the behavioral effects of attentional cueing survived feature swaps, providing evidence for an object-based attention mechanism. We also observed event-related potential correlates of these object-based selection effects in the late N1 component range, over occipital and parieto-occipital scalp sites, significantly associated with the variation in behavioral performance. Our findings provide the first evidence of the role of the N1 component in object-based attention in this transparent-motion design under conditions that rule out possible feature-based explanations. Taken together, the present results highlight the substantial effects of selective attention on the processing of visual information after the initial entry of information into the visual system and before the completion of its processing.Item Open Access Emergency crowd simulation for outdoor environments(Pergamon Press, 2010) Oğuz, O.; Akaydın, A.; Yilmaz, T.; Güdükbay, UğurWe simulate virtual crowds in emergency situations caused by an incident, such as a fire, an explosion, or a terrorist attack. We use a continuum dynamics-based approach to simulate the escaping crowd, which produces more efficient simulations than the agent-based approaches. Only the close proximity of the incident region, which includes the crowd affected by the incident, is simulated. We use a model-based rendering approach where a polygonal mesh is rendered for each agent according to the agent's skeletal motion. To speed up the animation and visualization, we employ an offline occlusion culling technique. We animate and render a pedestrian model only if it is visible according to the static visibility information computed. In the pre-processing stage, the navigable area is decomposed into a grid of cells and the from-region visibility of these cells is computed with the help of hardware occlusion queries. © 2009 Elsevier Ltd. All rights reserved.Item Open Access Extraction of 3D navigation space in virtual urban environments(IEEE, 2005-09) Yılmaz, Türker; Güdükbay, UğurUrban scenes are one class of complex geometrical environments in computer graphics. In order to develop navigation systems for urban sceneries, extraction and cellulization of navigation space is one of the most commonly used technique providing a suitable structure for visibility computations. Surprisingly, there is not much work done for the extraction of the navigable area automatically. Urban models, except for the ones where the building footprints are used to generate the model, generally lack navigation space information. Because of this, it is hard to extract and discretize the navigable area for complex urban scenery. In this paper, we propose an algorithm for the extraction of navigation space for urban scenes in threedimensions (3D). Our navigation space extraction algorithm works for scenes, where the buildings are in high complexity. The building models may have pillars or holes where seeing through them is also possible. Besides, for the urban data acquired from different sources which may contain errors, our approach provides a simple and efficient way of discretizing both navigable space and the model itself. The extracted space can instantly be used for visibility calculations such as occlusion culling in 3D space. Furthermore, terrain height field information can be extracted from the resultant structure, hence providing a way to implement urban navigation systems including terrains.Item Open Access “Night Hawks” watching over the city: redeployment of night watchmen and the politics of public space in Turkey(Sage Publications, 2019-11) Batuman, Bülent; Erkip, FeyzanTechnological advances have enormously increased surveillance techniques in the last three decades. In this article, we scrutinize the re-instatement of bekçi, the traditional night watchmen patrolling the residential neighborhoods in Turkey, which was obsolete for decades. We analyze the re-emergence of the bekçi in relation to the dynamics of urbanization, and with a perspective of power and surveillance. Our discussion bridges the Foucauldian notion of “visibility,” equating it with being subject to surveillance, and the Arendtian emphasis on “appearance” as the precondition for a claim to public space (hence, citizenship) in order the uncover the role of visibility within the mechanisms of power in public space. We argue that although the bekçi seems outmoded, especially within the context of ever-increasing advancement of surveillance technologies; its recent deployment in the public spaces of Turkish metropolises brings about new modes of politics of visibility parallel to the changing modality of the urban environment.Item Open Access Power as visibility: conceptualizing the changing nature of influence in international relations(Bilkent University, 2024-06) Karabıçak, OnurThis thesis propounds a new definition of power and influence in international relations and a conceptual framework of power’s translation into influence. First, this thesis defines power as being or rendering something (in)visible, and influence as changing one's narrative of world politics. Visibility is being socially relevant and mattering to others, and it is operationalized as an actor's frequency of being seen by an audience. Second, this thesis draws a framework for the analysis of the power and influence of international actors on audiences. The methodology is extracted from the operationalization of the components of visibility in the proposed framework of analysis. The power as visibility framework is applied to the case of comparing Erdoğan's power and influence over the mass audience in Türkiye and the Western European elite audience in 2008 and 2020. The material examined by the thesis consists of official speeches and popular culture media. Finally, the thesis concludes with a discussion of the alternative explanations and power as visibility framework.Item Open Access Spatial attention and paracontrast masking(Bilkent University, 2021-01) Konyalı, AfifeVisual masking is a powerful methodological tool to investigate the dynamics of sensory processing associated with object visibility and identity. Previous paracontrast masking studies revealed three distinct components that have been proposed to reflect processes at different stages and to be mediated by the distinct interactions within and/or across pathways [1, 2]. The brief and prolonged inhibition components are mainly observed within short and long stimulus onset asynchronies (SOAs) and they have been interpreted as the reflectance of early lateral inhibition and late recurrent inhibition within the parvo-dominated P-pathway. On the other hand, the facilitation typically becomes dominant at intermediate SOAs and the excitatory modulations of sub-cortical structures on the parvo-dominated pathway have been proposed as the underlying mechanism. An important question to address is how attention modulates these components and associated processes. In this thesis, two experiments were designed to understand the effects of attention on the components involved in paracontrast masking. In the first experiment, using an experimental design [3] combined with a contour discrimination task, the set-size was varied to manipulate attention in the spatial domain. The paracontrast masking functions indicated robust brief and prolonged inhibitions. Importantly, the set-size differentially altered these components. An increase in set-size (i.e., attentional load in the visual field) decreased brief inhibition while increasing the prolonged inhibition. In a second experiment, a brightness/contrast matching task was used to understand the effects of attention on the facilitation. Although the paracontrast masking functions showed facilitation at intermediate SOAs and the component was higher for increased set-size condition, these observations were not supported by statistical tests. Taken together, these findings revealed differential effects of spatial attention on the inhibitory mechanisms operating at distinct stages of P-pathway. In the last part of the thesis, an elaborated experimental design was also proposed to further understand and reveal possible effects of attention on the facilitatory mechanism. Future neuroimaging studies will be informative to understand the neural correlates of attention and paracontrast interaction, and hence the role of attention in object visibility.Item Embargo The effects of generic and targeted visibility on work-process interactions in open-plan offices(Bilkent University, 2024-06) Yenel Güler, GizemVisibility within open-plan offices plays a crucial role in shaping employee behaviors, including how they interact. The main aim of this thesis is to investigate the impacts of generic and targeted visibility on work-process interactions in open-plan offices. In the first phase, adopting a qualitative approach, this study aimed to detect work-process interaction patterns through a survey in two open-plan offices with 30 employees. Survey questions related to work-process interactions were analyzed through axial analysis. The second phase of the study, adopting a quantitative approach, was conducted through generic and targeted visibility analysis and new codes written for DepthMapX. The outputs of the two phases were analyzed to comprehend the influence of generic and targeted visibility on work-process interactions in open-plan offices. The results showed that density values for 120° and 360° isovists are determinant factors for the number of work-process interactions in all generic and targeted visibility parameters. Moreover, a negative correlation was found between density parameters and the number of work-process interactions. Therefore, it was found that more visible employees per unit in 120° and 360° isovists result in fewer work process interactions in open-plan offices. In other words, it was found that when an employee has a desk with low visual privacy or high visibility, this employee avoids interacting with their colleagues in open-plan offices. Therefore, the study's findings reveal that the impact of visual privacy on work-process interactions in open-plan offices is not as same as previously thought. In conclusion, the results of this study suggest that more visibility does not result in more work-process interactions in open-plan offices unless employees’ visual privacy is preserved.Item Open Access A tool for pattern information extraction and defect quantification from crystal structures(Elsevier, 2015) Okuyan, E.; Okuyan, E.In this paper, we present a revised version of BilKristal 2.0 tool. We added defect quantification functionality to assess crystalline defects. We improved visualization capabilities by adding transparency support and runtime visibility sorting. Discovered bugs are fixed and small performance optimizations are made. New version program summary Program title: BilKristal 3.0 Catalogue identifier: ADYU-v3-0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADYU-v3-0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1868 923 No. of bytes in distributed program, including test data, etc.: 8854 507 Distribution format: tar.gz Programming language: C, C++, Microsoft.NET Framework 2.0 and OpenGL Libraries. Computer: Personal Computers with Windows operating system. Operating system: Windows XP or higher. RAM: 20-60 Megabytes. Classification: 8. Catalogue identifier of previous version: ADYU-v2-0 Journal reference of previous version: Comput. Phys. Comm. 185 (2014) 442 External routines: Microsoft.NET Framework 2.0. For the visualization tool, graphics card driver should also support OpenGL. Does the new version supersede the previous version?: Yes Nature of problem: Determining the crystal structure parameters of a material is a very important issue in crystallography. Knowing the crystal structure parameters helps the understanding of the physical behavior of material. For complex structures, particularly for materials which also contain local symmetry as well as global symmetry, obtaining crystal parameters can be very hard. Solution method: The tool extracts crystal parameters such as primitive vectors, basis vectors and identifies the space group from atomic coordinates of crystal structures. Reasons for new version: Additional features, Compatibility issues with newer development environments, Performance optimizations, Minor bug corrections. Summary of revisions:Defect quantification capability is added. The tool can process the imperfect crystal structures, finds and quantifies the crystalline defects. The tool is capable of finding positional defects, vacancy defects, substitutional impurities and interstitial impurities. The algorithms presented in [3] are used for defect quantification implementation.Transparency support is added to the visualization tool. Users are now allowed to set the transparency of each atom type individually.Runtime visibility sorting functionality is added to facilitate correct transparency computations.Visual Studio 2012 support is added. Visual Studio 2012 specific project files are created and the project is tested with this development environment.In visualization tool, an unused log file was created. This issue is corrected.In visualization tool, some OpenGL calls which are executed at every draw are changed to be executed only when they are needed, improving the visualization performance.Restrictions: Assumptions are explained in [1,2]. However, none of them can be considered as a restriction onto the complexity of the problem. Running time: The tool was able to process input files with more than a million atoms in less than 20 s on a PC with an Athlon quad-core CPU at 3.2 GHz using the default parameter values. References: [1] Erhan Okuyan, Ugur Güdükbay, Oguz Gülseren, Pattern information extraction from crystal structures, Comput. Phys. Comm. 176 (2007) 486. [2] Erhan Okuyan, Ugur Güdükbay, BilKristal 2.0: A tool for pattern information extraction from crystal structures, Comput. Phys. Comm. 185 (2014) 442. [3] Erhan Okuyan, Ugur Güdükbay, Ceyhun Bulutay, Karl-Heinz Heinig, MaterialVis: material visualization tool using direct volume and surface rendering techniques, J. Mol. Graphics Model. 50201450-60. © 2014 The Authors.Item Open Access Visibility-based assessment of urban form: an alternative perspective for the residential development in urban peripheries(Bilkent University, 2021-07) Cengu, SuardIt is highly important for urban designers to understand how the configuration of urban fabric influences the living experience of the city dwellers. While cities change through time, their evolution may produce spaces that may not have a positive contribution or don’t reach their full potential. We call these spaces as ‘lost spaces’. The fragmentation that has occurred as a result of master planning implementations in western development corridor of Ankara, has produced lost spaces. This thesis aims to assess spatial configurations of such spaces near residential buildings in Çayyolu. The chosen case study, Cayyolou, is a ‘developed’ area in Ankara which has been an outcome of the city’s urban expansion. Urban and architectural spaces are defined by the spatial relations and social synergy stimulated by visual interaction. We have considered visibility as an indicator of ‘positive space’ and used isovists as a tool that measures visibility levels. A space that can be seen from any vantage point is defined as isovist by, and a set of such spaces defines a visual field. By utilizing computational tools and geometrical properties of isovist and isovist fields, we can identify and improve visibility of selected areas. In addition to visibility assessment of existing conditions of selected sites, this framework provides some design interventions which help improve visibility and propounds a relationship between urban spaces and visibility.Item Open Access Youtube vlogs, stardom and LGBTQ community(Bilkent University, 2018-02) Gürsoy, Cihan AkınThis thesis analyzes the rising importance of YouTube vlogs and vloggers against mainstream media organs in terms of self-representation and affiliation. The research specifically focuses on LGBTQ individuals’ sexual identity and communication development created by coming out videos while establishing visibility and acculturation for the LGBTQ community through the discourse being used. The study also shows YouTube’s potential power to produce online stars as a role model for the audience and the ways these stars use their stardom power to raise more awareness on the LGBTQ issues.