Browsing by Author "Aman, Aytek"

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Open Access
Compact tetrahedralization-based acceleration structures for ray tracing
(Springer, 2022-10) Aman, Aytek; Demirci, Serkan; Güdükbay, Uğur
We propose compact and efficient tetrahedral mesh representations to improve the ray-tracing performance. We reorder tetrahedral mesh data using a space-filling curve to improve cache locality. Most importantly, we propose efficient ray-traversal algorithms. We provide details of the regular ray-tracing operations on tetrahedral meshes and the GPU implementation of our traversal method. We demonstrate our findings through a set of comprehensive experiments. Our method outperforms existing tetrahedral mesh-based traversal methods and yields comparable results to the traversal methods based on the state-of-the-art acceleration structures such as k-dimensional (k-d) tree and Bounding Volume Hierarchy (BVH) in terms of speed. Storage-wise, our method uses less memory than its tetrahedral mesh-based counterparts, thus allowing larger scenes to be rendered on the GPU. Graphic Abstract: [Figure not available: see fulltext.] © 2022, The Visualization Society of Japan.
Open Access
Model-based camera tracking for augmented reality
(2014) Aman, Aytek
Augmented reality (AR) is the enhancement of real scenes with virtual entities. It is used to enhance user experience and interaction in various ways. Educational applications, architectural visualizations, military training scenarios and pure entertainment-based applications are often enhanced by augmented reality to provide more immersive and interactive experience for the users. With hand-held devices getting more powerful and cheap, such applications are becoming very popular. To provide natural AR experiences, extrinsic camera parameters (position and rotation) must be calculated in an accurate, robust and efficient way so that virtual entities can be overlaid onto the real environments correctly. Estimating extrinsic camera parameters in real-time is a challenging task. In most camera tracking frameworks, visual tracking serve as the main method for estimating the camera pose. In visual tracking systems, keypoint and edge features are often used for pose estimation. For rich-textured environments, keypoint-based methods work quite well and heavily used. Edge-based tracking, on the other hand, is more preferable when the environment is rich in geometry but has little or no visible texture. Pose estimation for edge based tracking systems generally depends on the control points that are assigned on the model edges. For accurate tracking, visibility of these control points must be determined in a correct manner. Control point visibility determination is computationally expensive process. We propose a method to reduce computational cost of the edge-based tracking by preprocessing the visibility information of the control points. For that purpose, we use persistent control points which are generated in the world space during preprocessing step. Additionally, we use more accurate adaptive projection algorithm for persistent control points to provide more uniform control point distribution in the screen space. We test our camera tracker in different environments to show the effectiveness and performance of the proposed algorithm. The preprocessed visibility information enables constant time calculations of control point visibility while preserving the accuracy of the tracker. We demonstrate a sample AR application with user interaction to present our AR framework, which is developed for a commercially available and widely used game engine.
Open Access
Multi-level tetrahedralization-based accelerator for ray-tracing animated scenes
(John Wiley & Sons Ltd., 2021-06-01) Aman, Aytek; Demirci, Serkan; Güdükbay, Uğur; Wald, I.
We describe a hybrid acceleration structure for ray tracing. The hybrid structure is a Bounding Volume Hierarchy (BVH) where the leaf nodes are tetrahedralized for a decent ray-surface intersection performance. We use the hybrid acceleration structure (BTH) in a two-level acceleration structure for rendering animated scenes. There is a BVH at the top level in this two-level structure and the proposed hybrid structure (BTH) at the bottom level. We test the proposed two-level structure (BVH-BTH) for various animated scenes and obtained promising results against other acceleration structures in terms of rendering times. The two-level BVH-BTH structure outperforms the two-level BVH structure for the tested dynamic scenes.
Open Access
Out-of-core Constrained Delaunay Tetrahedralizations for Large Scenes
(Springer, Cham, 2021-05-07) Erkoç, Ziya; Aman, Aytek; Güdükbay, Uğur; Si, H.
Tetrahedralization algorithms are used for many applications such as Ray Tracing and Finite Element Methods. For most of the applications, constrained tetrahedralization algorithms are chosen because they can preserve input triangles. The constrained tetrahedralization algorithms developed so far might suffer from a lack of memory. We propose an out-of-core near Delaunay constrained tetrahedralization algorithm using the divide-and-conquer paradigm to decrease memory usage. If the expected memory usage is below the user-defined memory limit, we tetrahedralize using TetGen. Otherwise, we subdivide the set of input points into two halves and recursively apply the same idea to the two halves. When compared with the TetGen, our algorithm tetrahedralizes the point clouds using less amount of memory but takes more time and generates tetrahedralizations that do not satisfy the Delaunay criterion at the boundaries of the merged regions. We quantify the error using the aspect-ratio metric. The difference between the tetrahedralizations that our approach produce and the Delaunay tetrahedralization are small and the results are acceptable for most applications.
Open Access
Rendering three-dimensional scenes with tetrahedral meshes
(2022-07) Aman, Aytek
We propose compact and efficient tetrahedral mesh representations to improve the ray-tracing performance. We reorder tetrahedral mesh data using a space-filling curve to improve cache locality. Most importantly, we propose efficient ray traversal algorithms. We provide details of the regular ray tracing operations on tetrahedral meshes and the Graphics Processing Unit (GPU) implementation of our traversal method. We demonstrate our findings through a set of comprehensive experiments. Our method outperforms existing tetrahedral mesh-based traversal methods and yields comparable results to the traversal methods based on the state-of-the-art acceleration structures such as k-dimensional (k-d) tree and Bounding Volume Hierarchy (BVH) in terms of speed. Storage-wise, our method uses less memory than its tetrahedral mesh-based counterparts, thus allowing larger scenes to be rendered on the GPU. We also describe additional applications of our technique specifically for volume rendering, two-level hybrid acceleration structures for animation purposes, and point queries in two-dimensional (2-D) and three-dimensional (3-D) triangulations. Finally, we present a practical method to tetrahedralize very large scenes.