Veysi İşler

Retrospective adaptive prefetching for interactive Web GIS applications

A major task of a Web GIS (Geographic Information Systems) system is to transfer map data to client applications over the Internet, which may be too costly. To improve this inefficient process, various solutions are available. Caching the responses of the requests on the client side is the most commonly implemented solution. However, this method may not be adequate by itself. Besides caching the responses, predicting the next possible requests from a client and updating the cache with responses for those requests together provide a remarkable performance improvement. This procedure is called “prefetching” and makes caching mechanisms more effective and efficient. This paper proposes an efficient prefetching algorithm called Retrospective Adaptive Prefetch (RAP), which is constructed over a heuristic method that considers the former actions of a given user. The algorithm reduces the user-perceived response time and improves user navigation efficiency. Additionally, it adjusts the cache size automatically, based on the memory size of the client’s machine. RAP is compared with four other prefetching algorithms. The experiments show that RAP provides better performance enhancements than the other methods.

Subdivision of 3D Space Based on the Graph Partitioning for Parallel Ray Tracing

An approach for parallel ray tracing is to subdivide the 3D space into rectangular volumes and assign the object descriptions with their related computations in each volume to a different processor. The subdivision process is critical in reducing the interprocessor communication overhead, and maintaining the load balance among processors of a multicomputer. In this paper, after a brief overview of parallel ray tracing, a heuristic is proposed to subdivide the 3D space by converting the problem into a graph partitioning problem. The proposed algorithm tries to minimize the communication cost while maintaining a load balance among processors.

A Parallel Algorithm for UAV Flight Route Planning on GPU

Aerial surveillance missions require a geographical region known as the area of interest to be inspected. The route that the aerial reconnaissance vehicle will follow is known as the flight route. Flight route planning operation has to be done before the actual mission is executed. A flight route may consist of hundreds of pre-defined geographical positions called waypoints. The optimal flight route planning manages to find a tour passing through all of the waypoints by covering the minimum possible distance. Due to the combinatorial nature of the problem it is impractical to devise a solution using brute force approaches. This study presents an approach to find a near-optimal solution to the flight route planning problem. The proposed approach is based on converting the problem into Traveling Salesman Problem which is solved using Genetic Algorithms on Graphical Processing Unit (GPU). The parallel genetic algorithm devised for GPUs has been compared to the alternative algorithms and found to be promising in terms of speed-up. We also present a thorough analysis of the implemented algorithm for several cases using different parameter values.

The Virtual Marathon: Parallel Computing Supports Crowd Simulations

To be realistic, an urban model must include appropriate numbers of pedestrians, vehicles, and other dynamic entities. Using a parallel computing architecture, researchers simulated a marathon with more than a million participants. To simulate participant behavior, they used fuzzy logic on a GPU to perform millions of inferences in real time.

Acceptance of virtual worlds as learning space

This study investigated relationships among perceived usefulness (PU), ease of use and perceived enjoyment, plus their relationships with the behavioural intention (BI) of individuals to use virtual worlds as a learning space. Participant responses to a questionnaire were analysed, and results indicated that while PU seemed to affect BIs most, perceived enjoyment (PE) and ease of use also played a role. Moreover, PE and ease of use also affected PU. Namely, if students found a virtual world enjoyable and easy to use, they perceived it as useful for learning and performance. In addition, the effect of PE on perceived ease of use showed that if students found a virtual world enjoyable, they underestimated difficulties using it. Findings highlighted important issues for the acceptance and adoption of virtual worlds as learning spaces.

Dynamic view-dependent visualization of unstructured tetrahedral volumetric meshes

Visualization of large volumetric datasets has always been an important problem. Due to the high computational requirements of volume-rendering techniques, achieving interactive rates is a real challenge. We present a selective refinement scheme that dynamically refines the mesh according to the camera parameters. This scheme automatically determines the impact of different parts of the mesh on the output image and refines the mesh accordingly, without needing any user input. The view-dependent refinement scheme uses a progressive mesh representation that is based on an edge collapse-based tetrahedral mesh simplification algorithm. We tested our view-dependent refinement framework on an existing state-of-the-art volume renderer. Thanks to low overhead dynamic view-dependent refinement, we achieve interactive frame rates for rendering common datasets at decent image resolutions.Graphical Abstract

Acceleration of direct volume rendering with programmable graphics hardware

We propose a method to accelerate direct volume rendering using programmable graphics hardware (GPU). In the method, texture slices are grouped together to form a texture slab. Rendering non-empty slabs from front to back viewing order generates the resultant image. Considering each pixel of the image as a ray, slab silhouette maps (SSMs) are used to skip empty spaces along the ray direction per pixel basis. Additionally, SSMs contain terminated ray information. The method relies on hardware z-occlusion culling and hardware occlusion queries to accelerate ray traversals. The advantage of this method is that SSMs are created on the fly by the GPU without any pre-processing. The cost of generating the acceleration structure is very small with respect to the total rendering time.

Fast ray tracing 3D models

Abstract In many computer graphics applications such as CAD, realistic displays have very important and positive effects on the users of the system. There are several techniques to generate realistic images with the computer. Ray tracing gives the most effective results by simulating the interaction of light with its environment. However, it may require an excessive amount of time to generate an image. In this article, we present a survey of methods developed to speed up the ray tracing algorithm and introduce a fast ray tracer to process a 3D scene that is defined by interactive 3D modeling software.

Developing a Validation Methodology for Educational Driving Simulators and a Case Study

The aim of this study is to develop a methodology for validating driving simulators in terms of simulator usability. The methodology was used to validate a truck simulator designed for training truck drivers about economic fuel consumption. The participants were eight truck drivers. Interview and observation methods were used to gather data. The results of the study showed that drivers did not have difficulty to recognize the parts of the driving simulator. Also, they stated that driving the simulator was easy. However, they said that they had some difficulties to use some systems of the simulator.

Acceleration of regular grid traversals using extended chessboard distance transformation on GPU

In the recent years graphics processing units (GPU) have evolved into general purpose programmable streaming parallel processors. This evolution makes it possible to implement high quality photo realistic rendering techniques on graphics processors. There have been a few studies to show how to map ray tracing to the GPU. Since graphics processors are not designed to process complex data structures, it is crucial to explore data structures and algorithms for efficient stream processing. In particular ray traversal is one of the most time consuming parts of ray tracing methods. In this work we focus on the efficient ray traversals on GPU. Several known techniques have been redesigned and adapted to the GPU programming model. Also a new traversal method based on extended anisotropic chessboard distance metric has been introduced.