Papers by Vlastimil Havran
In this report we present an experimental eciency study of spatial subdivision schemes for ray-sh... more In this report we present an experimental eciency study of spatial subdivision schemes for ray-shooting acceleration. Presented results are part of our eort to nd the long-discussed best eciency scheme from the statistical point of view. We propose four testing procedures evaluating the ray-shooting algorithm properties. We use these methods to produce hardware independent statistics for dierent ray-shooting acceleration schemes that have been reimplemented following the published literature. We dene the the minimal set of parameters to be reported as well as scene invariants, parameters that stay the same regardless of the acceleration scheme used. The main results of rst 1440 measurements for 30 scenes from the SPD database and 12 acceleration methods are reported. We also attempt to outline a method that suggests the most suitable acceleration scheme based on the scene complexity analysis of a given scene. 1. Introduction Ray-shooting algorithm is one of fundamental...
Ray Maps for Global Illumination in Rendering Techniques 2005
Eurographics Symposium on Rendering/Eurographics Workshop on Rendering Techniques, 2005
We describe a novel data structure for representing light transport called ray map. The ray map e... more We describe a novel data structure for representing light transport called ray map. The ray map extends the concept of photon maps: it stores not only photon impacts but the whole photon paths. We demonstrate the utility of ray maps for global illumination by eliminating boundary bias and reducing topological bias of density estimation in global illumination. Thanks to the
International Conference in Central Europe on Computer Graphics and Visualization, 2002
Efficient ray shooting algorithm is inherently required by many computer graphics algorithms, par... more Efficient ray shooting algorithm is inherently required by many computer graphics algorithms, particularly in image synthesis. Practical ray shooting algorithms aiming at the average-case complexity use some underlying spatial data structure such as -tree. We show the new termi- nation criteria algorithm that improves the space and time complexity of the -tree construction. It provides efficient ray-shooting queries and does
Optimal combination of techniques in multiple importance sampling
Proceedings of the 13th ACM SIGGRAPH International Conference on Virtual-Reality Continuum and its Applications in Industry - VRCAI '14, 2014
Proceedings of the 21st spring conference on Computer graphics - SCCG '05, 2005
ceiling floortile pinkwall walkway painted agglomerate granite polished ceramic plastic with a gl... more ceiling floortile pinkwall walkway painted agglomerate granite polished ceramic plastic with a glossy varnish Figure 1: Four material samples as the subject of the validation. The samples are referred by their location in a building.
Proceedings of the 21st spring conference on Computer graphics - SCCG '05, 2005
Raytracing has become a popular method for generating realistic images and movies. The progress i... more Raytracing has become a popular method for generating realistic images and movies. The progress in hardware development shows that the real time raytracing on a single PC might be possible in the ongoing future. Obviously, that new generation of raytracing based applications will require more visualization precision and flexibility. Most of the modern raytracing based applications only deal with triangles as basic primitives, which brings limitations to an application and may cause visual artifacts to appear. NURBS surface representation is common for most of 3D modeling tools because of its compactness and useful geometric properties of NURBS surfaces. Using the direct raytracing NURBS surfaces, one can achieve better quality of rendered images. Although, many such approaches have already been presented, almost all of them suffer from numerical problems or do not work in some special cases. This paper presents a modified Bézier clipping method for finding ray -NURBS surface intersection points, which is fast, robust, and numerically stable.
2006 IEEE Symposium on Interactive Ray Tracing, 2006
Though a large variety of efficiency structures for ray tracing exist, kd-trees today seem to slo... more Though a large variety of efficiency structures for ray tracing exist, kd-trees today seem to slowly become the method of choice. In particular, kd-trees built with cost estimation functions such as a surface area heuristic (SAH) seem to be important for reaching high performance. Unfortunately, most algorithms for building such trees have a time complexity of O(N log 2 N), or even O(N 2 ). In this paper, we analyze the state of the art in building good kd-trees for ray tracing, and eventually propose an algorithm that builds SAH kd-trees in O(N logN), the theoretical lower bound.
Bounding volume hierarchies versus kd-trees on contemporary many-core architectures
Proceedings of the 30th Spring Conference on Computer Graphics - SCCG '14, 2014
Computers & Graphics, 2015
We propose a new method for incremental construction of Bounding Volume Hierarchies (BVH). Despit... more We propose a new method for incremental construction of Bounding Volume Hierarchies (BVH). Despite the wide belief that the incremental construction of BVH is inefficient we show that our method incrementally constructs a BVH with quality comparable to the best SAH builders. We illustrate the versatility of the proposed method using a flexible parallelization scheme that opens new possibilities for combining different BVH construction heuristics. We demonstrate the usage of the method in a proof-ofconcept application for real-time preview of data streamed over the network. We believe that our method will renew the interest in incremental BVH construction and it will find its applications in ray tracing based remote visualizations and fast previews or in interactive scene editing applications handling very large data sets.
Proceedings of the 23rd Spring Conference on Computer Graphics - SCCG '07, 2007
: (left) A ray casted view of interior of a larger scene. (center) Visualization of the number of... more : (left) A ray casted view of interior of a larger scene. (center) Visualization of the number of nodes traversed per ray for the traditional traversal algorithm. (right) The same visualization for our new algorithm. The dark blue color corresponds to zero traversal steps, dark red corresponds to 255 or more traversal steps per ray. Note that the new algorithm significantly reduces the number of traversals per ray.
2006 IEEE Symposium on Interactive Ray Tracing, 2006
In this paper we will address the problem of fast construction of spatial hierarchies for ray tra... more In this paper we will address the problem of fast construction of spatial hierarchies for ray tracing with applications in animated environments including non-rigid animations. We will discuss the properties of currently used techniques with O(N log N) construction time for kd-trees and bounding volume hierarchies. Further, we will propose a hybrid data structure blending a spatial kd-tree with bounding volume primitives. We will keep our novel hierarchical data structures algorithmically efficient and comparable with kd-trees by using a cost model based on surface area heuristics. Although the time complexity O(N log N) is a lower bound required for construction of any spatial hierarchy that corresponds to sorting based on comparisons, using approximate method based on space discretization, we propose novel hierarchical data structures with an expected O(N log log N) time complexity. We will also discuss constants behind the construction algorithms of spatial hierarchies important in practice. We have documented the performance of our algorithms by results obtained from implementation on nine scenes.
Proceedings of the 18th spring conference on Computer graphics - SCCG '03, 2003
We present a technique that aims at exploiting temporal coherence of ray casted walkthroughs. Our... more We present a technique that aims at exploiting temporal coherence of ray casted walkthroughs. Our goal is to reuse ray/object intersections computed in the last frame of the walkthrough for acceleration of ray casting in the current frame. In particular we aim at eliminating the ray traversal and computing only a single ray/object intersection per pixel. If our technique does not succeed in determining visibility, it falls back to the classical ray traversal. Visible point samples from the last frame are reprojected to the current frame. To identify whether these samples can be reused we apply splatting and epipolar geometry constraints. We discuss two additional techniques that handle correct appearance of small objects. We conducted a series of tests on walkthroughs of building interiors. Our method succeeded in determining visibility of more than 78% of pixels. For these pixels only a single ray/object intersection is executed. The frame rate is increased by up to 47%. Finally, we argue that the achieved speedup is relatively significant by comparing the performance of our algorithm to the "ideal" ray shooting algorithm.
Proceedings. Computer Graphics International (Cat. No.98EX149), 1998
In the scope of rendering complex models with high depth complexity, it is of great importance to... more In the scope of rendering complex models with high depth complexity, it is of great importance to design outputsensitive algorithms, i.e., algorithms with the time complexity proportional to the number of visible graphic primitives in the resulting image. In this paper an algorithm allowing efficient culling of the invisible portion of the rendered model is presented. Our approach uses a spatial hierarchy to represent the topology of the model. For a current viewpoint a set of polygonal occluders is determined that are used to build the occlusion tree. In the occlusion tree occlusion volumes of the selected occluders are merged. Visibility from the viewpoint is determined by processing the spatial hierarchy and classifying the visibility of its regions. In this process the occlusion tree is used to determine the viewpoint-to-region visibility efficiently. The algorithm is well-suited for complex models where large occluders are present.
Exploiting temporal and spatial coherence in hierarchical visibility algorithms
Proceedings Spring Conference on Computer Graphics, 2001
Abstract: We present a series of simple improvements that make use of temporal and spatial cohere... more Abstract: We present a series of simple improvements that make use of temporal and spatial coherence in the scope of hierarchical visibility algorithms. The hierarchy updating avoids visibility tests of certain interior nodes of the hierarchy. The visibility propagation algorithm reuses information about visibility of neighbouring spatial regions. Finally, the conservative hierarchy updating avoids visibility tests of the hierarchy nodes
Lecture Notes in Computer Science, 2004
Complex procedural shaders are commonly used to enrich the appearance of high-quality computer an... more Complex procedural shaders are commonly used to enrich the appearance of high-quality computer animations. In traditional rendering architectures the shading computation is performed independently for each animation frame which leads to significant costs. In this paper we propose an approach which eliminates redundant computation between subsequent frames by exploiting temporal coherence in shading. The shading computation is decomposed into view-dependent and viewindependent parts and the results of the latter one are shared by a number of subsequent frames. This leads to a significant improvement of the computation performance. Also, the visual quality of resulting animations is much better due to the reduction of temporal aliasing in shading patterns.
We propose a framework that captures multiple high dynamic range environment maps and decomposes ... more We propose a framework that captures multiple high dynamic range environment maps and decomposes them into sets of directional light sources in real-time. The environment maps, captured and processed on stand-alone devices (e.g. Nokia N900 smartphone), are available to rendering engines via a server that provides wireless access. We compare three different importance sampling techniques in terms of the quality of sampling pattern, temporal coherence, and performance. Furthermore, we propose a novel idea of merging the directional light sources from multiple cameras by interpolation. We then discuss the pros and cons when using multiple cameras.
Register Efficient Memory Allocator for GPUs
Statistical Characterization of Surface Reflectance
A custom designed density estimation method for light transport
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Papers by Vlastimil Havran