[show abstract][hide abstract] ABSTRACT: The precise modeling of vascular structures plays a key role in medical imaging applications, such as diagnosis, therapy planning and blood flow simulations. For the simulation of blood flow in particular, high-precision models are required to produce accurate results. It is thus common practice to perform extensive manual data polishing on vascular segmentations prior to simulation. This usually involves a complex tool chain which is highly impractical for clinical on-site application. To close this gap in current blood flow simulation pipelines, we present a novel technique for interactive vascular modeling which is based on implicit sweep surfaces. Our method is able to generate and correct smooth high-quality models based on geometric centerline descriptions on the fly. It supports complex vascular free-form contours and consequently allows for an accurate and fast modeling of pathological structures such as aneurysms or stenoses. We extend the concept of implicit sweep surfaces to achieve increased robustness and applicability as required in the medical field. We finally compare our method to existing techniques and provide case studies that confirm its contribution to current simulation pipelines.
IEEE transactions on visualization and computer graphics. 12/2013; 19(12):2828-37.
[show abstract][hide abstract] ABSTRACT: Hardware tessellation is one of the latest GPU features. Triangle or quad meshes are tessellated on-the-fly, where the tessellation level is chosen adaptively in a separate shader. The hardware tessellator only generates topology; attributes such as positions or texture coordinates of the newly generated vertices are determined in a domain shader. Typical applications of hardware tessellation are view dependent tessellation of parametric surfaces and displacement mapping. Often, the attributes for the newly generated vertices are stored in textures, which requires uv unwrapping, chartification, and atlas generation of the input meshâa process that is time consuming and often requires manual intervention. In this paper, we present an alternative representation that directly stores optimized attribute values for typical hardware tessellation patterns and simply assigns these attributes to the generated vertices at render time. Using a multilevel fitting approach, the attribute values are optimized for several resolutions. Thereby, we require no parameterization, save memory by adapting the density of the samples to the content, and avoid discontinuities by construction. Our representation is optimally suited for displacement mapping: it automatically generates seamless, view-dependent displacement mapped models. The multilevel fitting approach generates better low-resolution displacement maps than simple downfiltering. By properly blending levels, we avoid artifacts such as popping or swimming surfaces. We also show other possible applications such as signal-optimized texturing or light baking. Our representation can be evaluated in a pixel shader, resulting in signal adaptive, parameterization-free texturing, comparable to PTex or Mesh Colors. Performance evaluation shows that our representation is on par with standard texture mapping and can be updated in real time, allowing for application such as interactive sculpting.
IEEE transactions on visualization and computer graphics. 09/2013; 19(9):1488-1498.
[show abstract][hide abstract] ABSTRACT: We present a novel representation for storing sub-triangle signals, such as colors, normals, or displacements directly with the triangle mesh. Signal samples are stored as guided by hardware-tessellation patterns. Thus, we can directly render from our representation by assigning signal samples to attributes of vertices generated by the hardware tessellator. Contrary to texture mapping, our approach does not require any atlas generation, chartification, or uv-unwrapping. Thus, it does not suffer from texture-related artifacts, such as discontinuities across chart boundaries or distortion. Moreover, our approach allows specifying the optimal sampling rate adaptively on a per triangle basis, resulting in significant memory savings for most signal types. We propose a signal optimal approach for converting arbitrary signals, including existing assets with textures or mesh colors, into our representation. Further, we provide efficient algorithms for mip-mapping, bi- and tri-linear interpolation directly in our representation. Our approach is optimally suited for displacement mapping: it automatically generates crack-free, view-dependent displacement mapped models enabling continuous level-of-detail.
IEEE Transactions on Visualization and Computer Graphics 08/2013; 19(9):1488-1498. · 1.90 Impact Factor
[show abstract][hide abstract] ABSTRACT: We propose a novel method for local displacement events in large scenes, such as scratches, footsteps, or sculpting operations. Deformations are stored as displacements for vertices generated by hardware tessellation. Adaptive mesh refinement, application of the displacement and all involved memory management happen completely on the GPU. We show various extensions to our approach, such as on-the-fly normal computation and multi-resolution editing. In typical game scenes we perform local deformations at arbitrary positions in far less than one millisecond. This makes the method particularly suited for games and interactive sculpting applications.
Proceedings of the ACM SIGGRAPH Symposium on High Performance Graphics, Anaheim, CA; 07/2013
[show abstract][hide abstract] ABSTRACT: Hardware tessellation is one of the latest GPU features. Triangle or quad meshes are tessellated on-the-fly, where the tessellation level is chosen adaptively in a separate shader. The hardware tessellator only generates topology; attributes such as positions or texture coordinates of the newly generated vertices are determined in a domain shader. Typical applications of hardware tessellation are view dependent tessellation of parametric surfaces and displacement mapping. Often, the attributes for the newly generated vertices are stored in textures, which requires uv unwrapping, chartification, and atlas generation of the input mesh - a process that is time consuming and often requires manual intervention. In this paper, we present an alternative representation that directly stores optimized attribute values for typical hardware tessellation patterns and simply assigns these attributes to the generated vertices at render time. Using a multi-level fitting approach, the attribute values are optimized for several resolutions. Thereby, we require no parameterization, save memory by adapting the density of the samples to the content, and avoid discontinuities by construction.
IEEE transactions on visualization and computer graphics. 02/2013;
[show abstract][hide abstract] ABSTRACT: Existing GPU antialiasing techniques, such as MSAA or MLAA, focus on reducing aliasing artifacts along silhouette boundaries or edges in image space. However, they neglect aliasing from shading in case of high-frequency geometric detail. This may lead to a shading aliasing artifact that resembles Bailey's Bead Phenomenon—the degradation of continuous specular highlights to a string of pearls. These types of artifacts are particularly striking for high-quality surfaces. So far, the only way of removing aliasing from shading is by globally supersampling the entire image with a large number of samples. However, globally supersampling the image is slow and significantly increases bandwidth consumption. We propose three adaptive approaches that locally supersample triangles only where necessary on the GPU. Thereby, we efficiently remove artifacts from shading while aliasing along silhouettes is reduced by efficient hardware MSAA.
[show abstract][hide abstract] ABSTRACT: Abdominal aortic aneurysms are a common disease of the aorta which are
treated minimally invasive in about 33 % of the cases. Treatment is done
by placing a stent graft in the aorta to prevent the aneurysm from
growing. Guidance during the procedure is facilitated by fluoroscopic
imaging. Unfortunately, due to low soft tissue contrast in X-ray images,
the aorta itself is not visible without the application of contrast
agent. To overcome this issue, advanced techniques allow to segment the
aorta from pre-operative data, such as CT or MRI. Overlay images are
then subsequently rendered from a mesh representation of the
segmentation and fused to the live fluoroscopic images with the aim of
improving the visibility of the aorta during the procedure. The current
overlay images typically use forward projections of the mesh
representation. This fusion technique shows deficiencies in both the 3-D
information of the overlay and the visibility of the fluoroscopic image
underneath. We present a novel approach to improve the visualization of
the overlay images using non-photorealistic rendering techniques. Our
method preserves the visibility of the devices in the fluoroscopic
images while, at the same time, providing 3-D information of the fused
volume. The evaluation by clinical experts shows that our method is
preferred over current state-of-the-art overlay techniques. We compared
three visualization techniques to the standard visualization. Our
silhouette approach was chosen by clinical experts with 67 %, clearly
showing the superiority of our new approach.
[show abstract][hide abstract] ABSTRACT: In real-time rendering, global lighting information that is too expensive to be computed on the fly is typically pre-computed and baked as vertex attributes or into textures. Prominent examples are view independent effects, such as ambient occlusion, shadows, indirect lighting, or radiance transfer coefficients. Vertex baking usually requires less memory, but exhibits artifacts on large triangles. These artifacts are avoided by baking lighting information into textures, but at the expense of significant memory consumption and additional work to obtain a parameterization. In this paper, we propose a memory efficient and performant hybrid approach that combines texture- and vertex-based baking. Cheap vertex baking is applied by default and textures are used only where vertex baking is insufficient to represent the signal. Seams at transitions between both representations are hidden using a simple shader which smoothly blends between vertex- and texture-based shading. With our fully automatic approach, we can significantly reduce memory requirements without negative impact on rendering quality or performance.
[show abstract][hide abstract] ABSTRACT: This work presents the design and implementation of a massively parallel 3-SAT solver, specifically targeting random problem instances. Our approach is deterministic and features very little communication overhead and basically no load-balancing cost at all. In the context of most current parallel SAT solvers running only on a handful of cores, we implemented our solver on Nvidia's CUDA platform, utilizing more than 200 parallel streaming processors, and employing several millions of threads to work through single problem instances. As most common sequential solver techniques had to be discarded, our approach is additionally supported by a new set of global heuristics, designed specifically to be easily exploited by the underlying thread parallelism.
High Performance Computing and Simulation (HPCS), 2010 International Conference on; 08/2010
[show abstract][hide abstract] ABSTRACT: We present a novel hybrid rendering method for diffuse and glossy indirect illumination. A scene is rendered using standard
rasterization on a GPU. In a shader, secondary ray queries are used to sample incident light and to compute indirect lighting.
We observe that it is more important to cast many rays than to have precise results for each ray. Thus, we approximate secondary
rays by intersecting them with precomputed layered depth images of the scene. We achieve interactive to real-time frame rates
including indirect diffuse and glossy effects.
The Visual Computer 01/2010; 26:679-686. · 0.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Virtual environments are typically textured by manually choosing an image to apply on each surface. This implies browsing through large sets of generic textures for each and every surface in the scene. We propose to facilitate this long and tedious process. Our algorithm assists the user while he assigns textures to surfaces. Each time an image is chosen for a surface, our algorithm propagates this information throughout the entire environment. Our approach is based on a new surface similarity measure. We exploit this measure in an algorithm ranking all possible textures for a given surface. Hence, we do not simply assign a texture to the surface but also propose an ordered list of choices for the user. In the unavoidable event of an ambiguous choice, the user can quickly make a decision and select the best texture. Our algorithm is fast enough to allow for interactive feedback. Applications range from assisted interactive texturing to fully automatic initial texturing solutions.
Proceedings of the 2010 Symposium on Interactive 3D Graphics, SI3D 2010, February 19-21, 2010, Washington, DC, USA; 01/2010
[show abstract][hide abstract] ABSTRACT: In this paper we analyze normal vector representations. We derive the error of the most widely used representation, namely 3D floating-point normal vectors. Based on this analysis, we show that, in theory, the discretization error inherent to single precision floating-point normals can be achieved by 250.2 uniformly distributed normals, addressable by 51 bits. We review common sphere parameterizations and show that octahedron normal vectors perform best: they are fast and stable to compute, have a controllable error, and require only 1 bit more than the theoretical optimal discretization with the same error.
Computer Graphics Forum 01/2010; 29:1405-1409. · 1.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: Many algorithms exist which generate per-pixel geometry by selectively discarding fragments generated for a simple bounding geometry. On the other hand, multisampling support has become ubiquitous and is almost free in current graphics hardware. In this paper we leverage the ability of setting a pixel's coverage mask in the pixel shader to make seemingly inherently pixel-based per-pixel geometry approaches compatible with multisampled antialiasing. We consider both the rendering of curve regions as well as displacement mapping with antialiased outer and inner silhouettes.