The physics of volume rendering

Radiation transfer is an important topic in several physical disciplines, probably most prominently in astrophysics. Computer scientists use radiation transfer, among other things, for the visualisation of complex data sets with direct volume rendering. In this note, I point out the connection between physical radiation transfer and volume rendering, and I describe an implementation of direct volume rendering in the astrophysical radiation transfer code RADMC-3D. I show examples for the use of this module on analytical models and simulation data

Modern Real-time Volumetric Techniques

Import 03/11/2016V dnešní době jsou volumetrická data využívána v mnoha oblastech, převážně však lékařství nebo fyzice. Z tohoto důvodu je vizualizace těchto dat častým předmětem zájmu různých vědeckých publikací. Vzhledem k rostoucímu výkonu grafických karet je častěji požadována vizualizace v reálném čase. V této práci jsou představeny vybrané techniky, které lze použít při vizualizaci volumetrických dat s využitím grafického hardwaru. Vybrané techniky představují paralelní způsob vizualizace a způsoby pro dosažení co nejlepšího výsledku nebo urychlení výpočtů. V rámci zlepšení výsledku vizualizace jsou hlavními tématy způsoby simulace osvětlení, které má na výsledek výrazný vliv. Praktickým výsledkem práce je aplikace, která slouží pro demonstraci implementovaných technik.Today volumetric data are used in many fields, especially in medicine or physics. For this reason there are many scientific publications interested in visualization of this kind of data. Due to increasing performance of graphic hardware visualization in real-time is often required. In this thesis many techniques which can be used for visualization of volumetric data with use of graphic hardware are performed. Chosen techniques are parallel principle for visualization and principles for getting best possible result or reducing calculation time. In order to improve visual quality of the result the principles for light simulation are performed as main themes due to significant influence on visualization result. Practical result of this thesis is application for demonstration of implemented techniques.460 - Katedra informatikyvýborn

Ray-traced radiative transfer on massively threaded architectures

In this thesis, I apply techniques from the field of computer graphics to ray tracing in astrophysical simulations, and introduce the grace software library. This is combined with an extant radiative transfer solver to produce a new package, taranis. It allows for fully-parallel particle updates via per-particle accumulation of rates, followed by a forward Euler integration step, and is manifestly photon-conserving. To my knowledge, taranis is the first ray-traced radiative transfer code to run on graphics processing units and target cosmological-scale smooth particle hydrodynamics (SPH) datasets. A significant optimization effort is undertaken in developing grace. Contrary to typical results in computer graphics, it is found that the bounding volume hierarchies (BVHs) used to accelerate the ray tracing procedure need not be of high quality; as a result, extremely fast BVH construction times are possible (< 0.02 microseconds per particle in an SPH dataset). I show that this exceeds the performance researchers might expect from CPU codes by at least an order of magnitude, and compares favourably to a state-of-the-art ray tracing solution. Similar results are found for the ray-tracing itself, where again techniques from computer graphics are examined for effectiveness with SPH datasets, and new optimizations proposed. For high per-source ray counts (≳ 104), grace can reduce ray tracing run times by up to two orders of magnitude compared to extant CPU solutions developed within the astrophysics community, and by a factor of a few compared to a state-of-the-art solution. taranis is shown to produce expected results in a suite of de facto cosmological radiative transfer tests cases. For some cases, it currently out-performs a serial, CPU-based alternative by a factor of a few. Unfortunately, for the most realistic test its performance is extremely poor, making the current taranis code unsuitable for cosmological radiative transfer. The primary reason for this failing is found to be a small minority of particles which always dominate the timestep criteria. Several plausible routes to mitigate this problem, while retaining parallelism, are put forward