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Dipl.-Inf. Marco Ament

Institut für Visualisierung und Datenanalyse
Karlsruher Institut für Technologie (KIT)

Am Fasanengarten 5
Gebäude 50.34

D-76131 Karlsruhe, Germany


Room: 136, 1. OG

Email: ament [at] kit.edu
Phone: +49 (0)721 / 608 47507
www: http://cg.ivd.kit.edu/ament/
           Google Scholar Profile


News:

I have moved to the Institute for Visualization and Data Analysis (IVD) at the Karlsruhe Institute of Technology (KIT).


Research:

 
  Direct Volume Rendering (Optical Models, Sampling and Reconstruction, Parallelization)
  Global Volume Illumination (Monte Carlo Simulation, Astronomical Visualization)
  High Performance Computing on GPUs (CUDA)
  Physically-based Simulations (Fluid Dynamics) and Visualizations (Flow Visualization)
  Numerical Solution of Ordinary and Partial Differential Equations

 


Projects:

 

 

 

Photo-realistic and Interactive Visualization of Astronomical Objects for Digital Planetariums
(DFG, "Astrographik")

Abstract: This DFG-funded project aims to model astrophysical objects physically consistent for lifelike and fast 3D visualization. Therefore, methods and algorithms are developed to reconstruct the spatial structure of various objects from astronomical observations and physical constraints to visualize them interactively with modern, high-resolution planetarium displays. Cosmological effects are visualized based on scientific facts in an accessible manner for the public.

More Details...



  Special
Achievements:
   
    2014  
     

Winner of Computer Graphics Forum 2014 Cover Image Contest

M. Ament, F. Sadlo, and D. Weiskopf. Computer Graphics Forum, Front Cover, 2014.
http://vcg.isti.cnr.it/cgf/winner.php?year=2014

    2013  
     

IEEE SciVis 2013 Honorable Mention Award

M. Ament, F. Sadlo, and D. Weiskopf. Ambient Volume Scattering. IEEE Transactions on Visualization and Computer Graphics, 19(12): 2936-2945, 2013. (Proceedings of IEEE Visualization 2013)

     

Informatik Spektrum Front Cover Image

M. Ament, F. Sadlo, and D. Weiskopf. Informatik Spektrum, 36(5): Front Cover, 2013.

 
    2012  
     

Evans & Sutherland Cooperation

S. Wenger, M. Ament, D. Weiskopf, and M. Magnor. DigiStar 5 Brochure, Volumetric Nebula Models, 2012.

    2009  
     

EGPGV Front Cover Image

M. Ament and W. Straßer. Proceedings of the Eurographics Symposium on Parallel Graphics and Visualization, Front Cover, 2009.


  Publications:    
    2014  
     

Low-Pass Filtered Volumetric Shadows

M. Ament, F. Sadlo, C. Dachsbacher, and D. Weiskopf
IEEE Transactions on Visualization and Computer Graphics, to appear, 2014.
(Proceedings of IEEE Visualization 2014)

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Abstract: We present a novel and efficient method to compute volumetric soft shadows for interactive direct volume visualization to improve the perception of spatial depth. By direct control of the softness of volumetric shadows, disturbing visual patterns due to hard shadows can be avoided and users can adapt the illumination to their personal and application-specific requirements. We compute the shadowing of a point in the data set by employing spatial filtering of the optical depth over a finite area patch pointing toward each light source. Conceptually, the area patch spans a volumetric region that is sampled with shadow rays; afterward, the resulting optical depth values are convolved with a low-pass filter on the patch. In the numerical computation, however, to avoid expensive shadow ray marching, we show how to align and set up summed area tables for both directional and point light sources. Once computed, the summed area tables enable efficient evaluation of soft shadows for each point in constant time without shadow ray marching and the softness of the shadows can be controlled interactively. We integrated our method in a GPU-based volume renderer with ray casting from the camera, which offers interactive control of the transfer function, light source positions, and viewpoint, for both static and time-dependent data sets. Our results demonstrate the benefit of soft shadows for visualization to achieve user-controlled illumination with many-point lighting setups for improved perception combined with high rendering speed.

 

 

     

Refractive Radiative Transfer Equation

M. Ament, C. Bergmann, and D. Weiskopf
ACM Transactions on Graphics, 33(2): 17:1-17:22, 2014.
(Presented at ACM SIGGRAPH 2014)

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Abstract: We introduce a refractive radiative transfer equation to the graphics community for the physically based rendering of participating media that have a spatially varying index of refraction. We review principles of geometric non-linear optics that are crucial to discuss a more generic light transport equation. In particular, we present an optical model that has an integral form suitable for rendering. We show rigorously that the continuous bending of light rays leads to a non-linear scaling of radiance. To obtain physically correct results, we build on the concept of basic radiance—known from discontinuous refraction—to conserve energy in such complex media. Furthermore, the generic model accounts for the reduction in the speed of light due to the index of refraction to render transient effects like the propagation of light echoes. We solve the refractive volume rendering equation by extending photon mapping with transient light transport in a refractive, participating medium. We demonstrate the impact of our approach on the correctness of rendered images of media that are dominated by spatially continuous refraction and multiple scattering. Furthermore, our model enables us to render visual effects like the propagation of light echoes or time-of-flight imagery that cannot be produced with previous approaches.

   

2013
 
     

Ambient Volume Scattering
IEEE SciVis 2013 Honorable Mention Award

M. Ament, F. Sadlo, and D. Weiskopf
IEEE Transactions on Visualization and Computer Graphics, 19(12): 2936-2945, 2013.
(Proceedings of IEEE Visualization 2013)

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Abstract: We present ambient scattering as a preintegration method for scattering on mesoscopic scales in direct volume rendering. Far-range scattering effects usually provide negligible contributions to a given location due to the exponential attenuation with increasing distance. This motivates our approach to preintegrating multiple scattering within a finite spherical region around any given sample point. To this end, we solve the full light transport with a Monte-Carlo simulation within a set of spherical regions, where each region may have different material parameters regarding anisotropy and extinction. This precomputation is independent of the data set and the transfer function, and results in a small preintegration table. During rendering, the look-up table is accessed for each ray sample point with respect to the viewing direction, phase function, and material properties in the spherical neighborhood of the sample. Our rendering technique is efficient and versatile because it readily fits in existing ray marching algorithms and can be combined with local illumination and volumetric ambient occlusion. It provides interactive volumetric scattering and soft shadows, with interactive control of the transfer function, anisotropy parameter of the phase function, lighting conditions, and viewpoint. A GPU implementation demonstrates the benefits of ambient scattering for the visualization of different types of data sets, with respect to spatial perception, high-quality illumination, translucency, and rendering speed.

   

2012
 
     

Book Chapter: GPU-Accelerated Visualization

M. Ament, S. Frey, C. Müller, S. Grottel, T. Ertl, and D. Weiskopf
Editors: E. W. Bethel, H. Childs, and C. Hansen. High Performance Visualization: Enabling Extreme-Scale Scientific Insight.
Chapman and Hall/CRC, ISBN-13: 978-1439875728, pages 223-260, 2012.

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Abstract: The visualization of large data is a computationally demanding task. The increase in performance and the flexible programmability have made graphics processing units (GPUs) an attractive platform to address large data visualization. The parallel architecture of GPUs and the low costs, coupled with high availability, have paved the way for this significant field of research. In this chapter, we review the fundamental principles of modern graphics hardware briefly before we summarize the latest research in GPU-based visualization techniques for stand-alone and cluster-based systems.

 

 

Spectral Analysis of Higher-Order and BFECC Texture Advection

R. Netzel, M. Ament, M. Burch, and D. Weiskopf
Proceedings of the Workshop on Vision, Modeling, and Visualization (VMV), pages 87-94, 2012.

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Abstract: We present a spectral analysis of higher-order texture advection in combination with Back and Forth Error Compensation and Correction (BFECC). Semi-Lagrangian techniques exhibit high numerical diffusion, which acts as a low-pass filter and tends to smooth out high frequencies. In the spatial domain, numerical diffusion leads to a loss of details and causes a blurred image. To reduce this effect, higher-order interpolation methods or BFECC can be employed separately. In this paper, we present a combination of both approaches and we analyze the quality of different compositions of higher-order interpolation schemes with and without BFECC. We employ radial power spectrum diagrams for different advection times and input textures to evaluate the conservation of the spectrum up to fifth-order polynomials. Our evaluation shows that the results of texture advection are improved by using higher-order interpolation.

 

 

     

Visualization of Astronomical Nebulae
via Distributed Multi-GPU Compressed Sensing Tomography

S. Wenger, M. Ament, S. Guthe, D. Lorenz, A. Tillmann, D. Weiskopf, and M. Magnor
IEEE Transactions on Visualization and Computer Graphics, 18(12): 2188-2197, 2012.
(Proceedings of IEEE Visualization 2012)

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Airfoil2

Airfoil2

Abstract: The 3D visualization of astronomical nebulae is a challenging problem since only a single 2D projection is observable from our fixed vantage point on Earth. We attempt to generate plausible and realistic looking volumetric visualizations via a tomographic approach that exploits the spherical or axial symmetry prevalent in some relevant types of nebulae. Different types of symmetry can be implemented by using different randomized distributions of virtual cameras. Our approach is based on an iterative compressed sensing reconstruction algorithm that we extend with support for position-dependent volumetric regularization and linear equality constraints. We present a distributed multi-GPU implementation that is capable of reconstructing high-resolution datasets from arbitrary projections. Its robustness and scalability are demonstrated for astronomical imagery from the Hubble Space Telescope. The resulting volumetric data is visualized using direct volume rendering. Compared to previous approaches, our method preserves a much higher amount of detail and visual variety in the 3D visualization, especially for objects with only approximate symmetry.

 

 

     

Interactive Visualization and Simulation of Astronomical Nebulae

S. Wenger, M. Ament, W. Steffen, N. Koning, D. Weiskopf, and M. Magnor
IEEE Computing in Science and Engineering, 14(3): 78-87, 2012.
http://dx.doi.org/10.1109/MCSE.2012.52

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Airfoil2

Abstract: Interactive visualization and simulation of astrophysical phenomena enable digital planetariums and television documentaries to take their spectators on a journey into deep space and explore the astronomical wonders of our universe in 3D.

 

 

     

GPU-Based Four-Dimensional General-Relativistic Ray Tracing

D. Kuchelmeister, T. Müller, M. Ament, G. Wunner, and D. Weiskopf
Computer Physics Communications, 183(10): 2282–2290, 2012.
http://dx.doi.org/10.1016/j.cpc.2012.04.030

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Airfoil2

Abstract: This paper presents a new general-relativistic ray tracer that enables image synthesis on an interactive basis by exploiting the performance of graphics processing units (GPUs). The application is capable of visualizing the distortion of the stellar background as well as trajectories of moving astronomical objects orbiting a compact mass. Its source code includes metric definitions for the Schwarzschild and Kerr spacetimes that can be easily extended to other metric definitions, relying on its object-oriented design. The basic functionality features a scene description interface based on the scripting language Lua, real-time image output, and the ability to edit almost every parameter at runtime. The ray tracing code itself is implemented for parallel execution on the GPU using NVidia’s Compute Unified Device Architecture (CUDA), which leads to performance improvement of an order of magnitude compared to a single CPU and makes the application competitive with small CPU cluster architectures.

   

2011
 
     

GPU-Based Two-Dimensional Flow Simulation Steering using Coherent Structures

M. Ament, S. Frey, F. Sadlo, T. Ertl, and D. Weiskopf
Proceedings of the 2nd International Conference on Parallel, Distributed, Grid and Cloud Computing for Engineering, paper 18, 2011.
http://dx.doi.org/10.4203/ccp.95.18

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Airfoil1

Airfoil2

Abstract: We present an exemplary steering system that performs 2D flow simulation and visualization on graphics processing units (GPUs). The topology of a vector field provides the overall structure and therefore lends itself for steering purposes. We build on the concept of Lagrangian coherent structures present as ridges in the finite-time Lyapunov exponent (FTLE). This allows to perform steering with respect to the true time-dependent dynamics in a given time scope. Based on the insights from the FTLE visualization, our CUDA-based implementation allows effective interactive manipulation of boundary conditions such as solid obstacles or velocity profiles.

 

 

     

Sort First Parallel Volume Rendering

B. Moloney, M. Ament, D. Weiskopf, and T. Möller
IEEE Transactions on Visualization and Computer Graphics, 17(8): 1164-1177, 2011.
http://doi.ieeecomputersociety.org/10.1109/TVCG.2010.116

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stage1_small

stage1_small

Abstract: Sort first distributions have been studied and used far less than sort last distributions for parallel volume rendering, especially when the data is too large to be replicated fully. We demonstrate that sort first distributions are not only a viable method of performing data scalable parallel volume rendering, but more importantly they allow for a range of rendering algorithms and techniques that are not efficient with sort last distributions. Several of these algorithms are discussed and two of them are implemented in a parallel environment: a new improved variant of early ray termination to speed up rendering when volumetric occlusion occurs and a volumetric shadowing technique that produces more realistic and informative images based on half angle slicing. Improved methods of distributing the computation of the load balancing and loading portions of a subdivided data set are also presented. Our detailed test results for a typical GPU cluster with distributed memory show that our sort first rendering algorithm outperforms sort last rendering in many scenarios.

   

2010
 
     

Direct Interval Volume Visualization

M. Ament, D. Weiskopf, and H. Carr
IEEE Transactions on Visualization and Computer Graphics, 16(6): 1505-1514, 2010.
(Proceedings of IEEE Visualization 2010)
http://doi.ieeecomputersociety.org/10.1109/TVCG.2010.145

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stage1_small

Abstract: We extend direct volume rendering with a unified model for generalized isosurfaces, also called interval volumes, allowing a wider spectrum of visual classification. We generalize the concept of scale-invariant opacity—typical for isosurface rendering—to semi-transparent interval volumes. Scale-invariant rendering is independent of physical space dimensions and therefore directly facilitates the analysis of data characteristics. Our model represents sharp isosurfaces as limits of interval volumes and combines them with features of direct volume rendering. Our objective is accurate rendering, guaranteeing that all isosurfaces and interval volumes are visualized in a crack-free way with correct spatial ordering. We achieve simultaneous direct and interval volume rendering by extending preintegration and explicit peak finding with data-driven splitting of ray integration and hybrid computation in physical and data domains. Our algorithm is suitable for efficient parallel processing for interactive applications as demonstrated by our CUDA implementation.

 

 

     

A Parallel Preconditioned Conjugate Gradient Solver for the Poisson Problem
on a Multi-GPU Platform

M. Ament, G. Knittel, D. Weiskopf, and W. Straßer
Proceedings of the 18th Euromicro Conference on Parallel, Distributed and Network-based Computing (PDP), pages 583-592, 2010.
http://doi.ieeecomputersociety.org/10.1109/PDP.2010.51

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Abstract: We present a parallel conjugate gradient solver for the Poisson problem optimized for multi-GPU platforms. Our approach includes a novel heuristic Poisson preconditioner which is well-suited for massively-parallel SIMD processing. Furthermore, we address the problem of limited transfer rates over typical data channels such as the PCI-express bus relative to the bandwidth requirements of powerful GPUs. Specifically, naïve communication schemes can severely reduce the achievable speedup in such communication-intense algorithms. For this reason, we employ overlapping memory transfers to establish a high level of concurrency and to improve scalability. We have implemented our model on a high-performance workstation with multiple hardware accelerators. We will discuss the mathematical principles, give implementation details, and present the performance and the scalability of the system.

   

 

2009

 
     

Dynamic Grid Refinement for Fluid Simulations on Parallel Graphics Architectures

M. Ament and W. Straßer
Proceedings of the Eurographics Symposium on Parallel Graphics and Visualization (EGPGV), pages 9-15, 2009.
http://dx.doi.org/10.2312/EGPGV/EGPGV09/009-015

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Cover of EGPGV Proceedings 2009

Abstract: We present a physically-based fluid simulation with dynamic grid refinement on parallel SIMD graphics hardware. The irregular and dynamic structure of an adaptive grid requires sophisticated memory access patterns as well as a decomposition of the problem for parallel processing and the distribution of tasks to multiple threads. In this paper, we focus on the representation and management of the dynamic grid on the graphics device for an efficient parallelization of the advection step and the iterative solving of the Poisson equation. In order to achieve high performance, we utilize the hardware’s capabilities like fast cache access and trilinear filtering. Furthermore, expensive data transfer between host and device is minimized to avoid a major bottleneck. We report results on the inherent overhead of the dynamic grid compared to an equivalent Cartesian grid. In addition, a visual simulation of smoke is presented with radiosity-based illumination and volume ray casting at interactive frame rates.

   

 

2008

 
     

Hardware Accelerated Fluid Dynamics with Adaptive Grid Refinement

M. Ament
WSI/GRIS, University of Tübingen, Diploma Thesis, 2008.

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Abstract: In this thesis, a physically-based fluid simulation with dynamic grid refinement parallel SIMD graphics hardware is presented. The irregular and dynamic structure of an adaptive grid requires sophisticated memory access patterns as well as a decomposition of the problem for parallel processing and the distribution of tasks to multiple threads. The focus of this thesis lies on the representation and management of the dynamic grid on the graphics device for an efficient parallelization of the advection step and the iterative solving of the Poisson equation. In order to achieve high performance, the hardware's capabilities like fast cache access and trilinear filtering are utilized. Furthermore, expensive data transfer between host and device is minimized to avoid a major bottleneck. Results on the inherent overhead of the dynamic grid compared to an equivalent Cartesian grid are reported. In addition, a visual simulation of smoke is presented with radiosity-based illumination and volume ray casting at interactive frame rates.



Reviews:

   
  Journals

Computer Graphics Forum (2013, 2014)
IEEE Transactions on Visualization and Computer Graphics (2013, 2014)
IEEE Computer Graphics and Applications (2010)
IEEE Transactions on Embedded Computing Systems (2011)
Journal of Computational and Applied Mathematics (2010)
Parallel Computing (2011)
The Visual Computer (2009)

 

 

Conferences

ACM SIGGRAPH (2011)
Computer Graphics International (2014)
Eurographics (2010, 2011, 2013)
Eurographics Symposium on Parallel Graphics and Visualization (2010, 2013)
EuroVis (2012, 2013)
IEEE Visualization (2011, 2012, 2013)
Grapp (2011)
High Performance Graphics (2010)
Motion in Games (2011)
PDP (2014)
Vision, Modeling and Visualization Workshop (2010)

 


Advised Thesis:

   
  2009

Diplomarbeit: Parallele Berechnungen der volumetrischen Beleuchtung astrophysikalischer Nebel auf GPU-Clustern
(finished)

Diplomarbeit: Globale Beleuchtung von punktbasierten Isoflächen mittels Antiradiance
(finished)

Diplomarbeit: GPU-basiertes 4D-Raytracing in der Allgemeinen Relativitätstheorie
(finished)

 

  2010

Diplomarbeit: Globale volumetrische Beleuchtung mit hierarchischer Mehrfachstreuung in partizipierenden Medien
(finished)

Studienarbeit: Globale Volumenbeleuchtung mit Photon Mapping und Path Tracing
(finished)

 

  2011 Diplomarbeit: Texturadvektion höherer Ordnung
(finished)


  2012

Diplomarbeit: Zeitabhängige Visualisierung von Lichtechos in partizipierenden Medien
(finished)

BSc-Arbeit: Visualisierung von planetarischen Nebeln in Celestia
(finished)


  2013 Diplomarbeit: Effiziente Vorberechnung von Lichtpfaden in partizipierenden Medien
(finished)



Teaching:

   
  WS 09/10

Übungen zur Vorlesung Modellierung und Animation

Studienprojekt Stellarkartographie

Informatiktag 2010 - Visualisierung von Fraktalen

 

  SS 10 Studienprojekt Stellarkartographie
  WS 10/11 Übungen zur Vorlesung Modellierung und Animation
  SS 11 Hauptseminar Visualisierung großer Datensätze

Tag der Wissenschaft 2011 - Interaktive Visualisierung | Strömungssimulation


  WS 11/12 Hauptseminar Volumenrendering
  SS 12 Übungen zur Vorlesung Bildsynthese

Tag der Wissenschaft 2012 - Interaktive Visualisierung | Strömungssimulation


  WS 12/13 Übungen zur Vorlesung Visualization in Science and Engineering

Informatiktag 2013 - Visualisierung von Fraktalen


Short CV:

   
  2000 Abitur at Gymnasium Plochingen.
  2000-2001 Civil service at Johanniterstift Plochingen.
  2001-2002

Professional training in cycling and holder of class-A licence.
Apprenticeship as C/C++ programmer.

  2002-2009

Study of computer science with physics as a minor subject at University of Tübingen.
Diploma thesis at WSI/GRIS (Prof. Straßer).

  2009-2014 Research Assistant at University of Stuttgart.
PhD Student at VISUS (Prof. Weiskopf).
  2014-present Research Fellow at Karlsruhe Institute of Technology.
PostDoc at IVD (Prof. Dachsbacher)