Filip Sadlo - Academia.edu (original) (raw)

Papers by Filip Sadlo

IEEE transactions on visualization and computer graphics, 2014

We present a novel scheme for progressive rendering in interactive visualization. Static settings... more We present a novel scheme for progressive rendering in interactive visualization. Static settings with respect to a certain image quality or frame rate are inherently incapable of delivering both high frame rates for rapid changes and high image quality for detailed investigation. Our novel technique flexibly adapts by steering the visualization process in three major degrees of freedom: when to terminate the refinement of a frame in the background and start a new one, when to display a frame currently computed, and how much resources to consume. We base these decisions on the correlation of the errors due to insufficient sampling and response delay, which we estimate separately using fast yet expressive heuristics. To automate the configuration of the steering behavior, we employ offline video quality analysis. We provide an efficient implementation of our scheme for the application of volume raycasting, featuring integrated GPU-accelerated image reconstruction and error estimation...

IEEE Transactions on Visualization and Computer Graphics, 2014

We present a novel and efficient method to compute volumetric soft shadows for interactive direct... more 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.

Mathematics and Visualization, 2014

Communications in Computer and Information Science, 2013

Mathematics and Visualization, 2011

Mathematics and Visualization, 2010

Lagrangian coherent structures play an important role in the analysis of unsteady vector fields b... more Lagrangian coherent structures play an important role in the analysis of unsteady vector fields because they represent the timedependent analog to vector field topology. Nowadays, they are often obtained as ridges in the finite-time Lyapunov exponent of the vector field. However, one drawback of this quantity is its very high computational cost because a trajectory needs to be computed for every sample in the space-time domain. One of the foci of this paper are Lagrangian coherent structures that are related to predefined regions such as boundaries, i.e. related to flow attachment and flow separation phenomena. It presents an efficient method for computing the finite-time Lyapunov exponent and its height ridges only in these regions, and in particular, grid advection for the efficient computation of time series of the finite-time Lyapunov exponent, exploiting temporal coherence.

Journal of Visualization, 2015

ABSTRACT Abstract Treating time as the third dimension of 2D time-dependent flow enables the appl... more ABSTRACT Abstract Treating time as the third dimension of 2D time-dependent flow enables the application of a wide variety of visualization techniques for 3D stationary vector fields. In the resulting space-time representation, 3D streamlines represent 2D pathlines of the original field. In this paper, we investigate the application of different streamline-based visualization concepts to the 3D space-time representation of 2D time-dependent flow. As a consequence, we obtain from each streamline-based concept a Galilean-invariant counterpart that takes the time dependence of the original field explicitly into account. We show the advantages of the overall approach for vortex analysis and the analysis of the dynamics of material lines. In particular, we employ the concept for the extraction of vortex centers, vortex core regions, and the visualization of material line dynamics using streamsurface integration and line integral convolution in the space-time field. We exemplify the utility of our visualization approach using two 2D time-dependent datasets that exhibit vortical flow. Graphical Abstract

2014 IEEE 4th Symposium on Large Data Analysis and Visualization (LDAV), 2014

Visualization in Biomedical Computing 1994, 1994

Proceedings of the Second International Conference on Parallel, Distributed, Grid and Cloud Computing for Engineering, 2011

We present an exemplary steering system that performs 2D flow simulation and visualization on gra... more 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.

Finite element-based electromagnetic field simulation strongly benefits from using edge-conformin... more Finite element-based electromagnetic field simulation strongly benefits from using edge-conforming representations of the electric field. In this paper we address the visualization of discrete field data resulting from such simulations on 10-node quadratic tetrahedral grids. The use of higher-order grids enables, on the one hand, the accurate approximation of curved interfaces between electromagnetic materials, and on the other hand, it allows for a more accurate computation of derived quantities such as Coulomb forces and related surface tensions. However, a major drawback so far has been the lack of appropriate visualization techniques-common visualization systems do not support this type of data-necessitating a resampling step with all the involved drawbacks, including artifacts in the form of imposed continuity across material boundaries. We introduce a visualization framework implemented as a set of ParaView plugins that evaluates edge-conforming data by means of vector basis functions. Based on this framework we present different visualization approaches for the investigation of the electric field at material boundaries. We demonstrate their utility using electrohydrodynamics simulations of a water droplet on the surface of a high voltage insulator, representing a twophase flow problem driven by strong electric fields.