4,764 research outputs found
Spatio-angular Minimum-variance Tomographic Controller for Multi-Object Adaptive Optics systems
Multi-object astronomical adaptive-optics (MOAO) is now a mature wide-field
observation mode to enlarge the adaptive-optics-corrected field in a few
specific locations over tens of arc-minutes.
The work-scope provided by open-loop tomography and pupil conjugation is
amenable to a spatio-angular Linear-Quadratic Gaussian (SA-LQG) formulation
aiming to provide enhanced correction across the field with improved
performance over static reconstruction methods and less stringent computational
complexity scaling laws.
Starting from our previous work [1], we use stochastic time-progression
models coupled to approximate sparse measurement operators to outline a
suitable SA-LQG formulation capable of delivering near optimal correction.
Under the spatio-angular framework the wave-fronts are never explicitly
estimated in the volume,providing considerable computational savings on
10m-class telescopes and beyond.
We find that for Raven, a 10m-class MOAO system with two science channels,
the SA-LQG improves the limiting magnitude by two stellar magnitudes when both
Strehl-ratio and Ensquared-energy are used as figures of merit. The
sky-coverage is therefore improved by a factor of 5.Comment: 30 pages, 7 figures, submitted to Applied Optic
An implementation of ray tracing algorithm for the multiprocessor machines
Ray Tracing is an algorithm for generating photo-realistic pictures of the 3D scenes, given scene description, lighting condition and viewing parameters as inputs. The algorithm is inherently convenient for parallelization and the simplest parallelization scheme is for the shared-memory parallel machines (multiprocessors). This paper presents two implementations of the algorithm developed by the authors for alike machines, one using the POSIX threads API and another one using the OpenMP API. The paper also presents results of rendering some test scenes using these implementations and discusses our parallel algorithm version efficiency
Hardware acceleration of photon mapping
PhD ThesisThe quest for realism in computer-generated graphics has yielded a range of algorithmic
techniques, the most advanced of which are capable of rendering images at close to photorealistic
quality. Due to the realism available, it is now commonplace that computer graphics are used in
the creation of movie sequences, architectural renderings, medical imagery and product
visualisations.
This work concentrates on the photon mapping algorithm [1, 2], a physically based global
illumination rendering algorithm. Photon mapping excels in producing highly realistic, physically
accurate images.
A drawback to photon mapping however is its rendering times, which can be significantly longer
than other, albeit less realistic, algorithms. Not surprisingly, this increase in execution time is
associated with a high computational cost. This computation is usually performed using the
general purpose central processing unit (CPU) of a personal computer (PC), with the algorithm
implemented as a software routine. Other options available for processing these algorithms
include desktop PC graphics processing units (GPUs) and custom designed acceleration hardware
devices.
GPUs tend to be efficient when dealing with less realistic rendering solutions such as rasterisation,
however with their recent drive towards increased programmability they can also be used to
process more realistic algorithms. A drawback to the use of GPUs is that these algorithms often
have to be reworked to make optimal use of the limited resources available.
There are very few custom hardware devices available for acceleration of the photon mapping
algorithm. Ray-tracing is the predecessor to photon mapping, and although not capable of
producing the same physical accuracy and therefore realism, there are similarities between the
algorithms. There have been several hardware prototypes, and at least one commercial offering,
created with the goal of accelerating ray-trace rendering [3]. However, properties making many of
these proposals suitable for the acceleration of ray-tracing are not shared by photon mapping.
There are even fewer proposals for acceleration of the additional functions found only in photon
mapping.
All of these approaches to algorithm acceleration offer limited scalability. GPUs are inherently
difficult to scale, while many of the custom hardware devices available thus far make use of large
processing elements and complex acceleration data structures.
In this work we make use of three novel approaches in the design of highly scalable specialised
hardware structures for the acceleration of the photon mapping algorithm. Increased scalability is
gained through:
ā¢ The use of a brute-force approach in place of the commonly used smart approach, thus
eliminating much data pre-processing, complex data structures and large processing units
often required.
ā¢ The use of Logarithmic Number System (LNS) arithmetic computation, which facilitates a
reduction in processing area requirement.
ā¢ A novel redesign of the photon inclusion test, used within the photon search method of
the photon mapping algorithm. This allows an intelligent memory structure to be used for
the search.
The design uses two hardware structures, both of which accelerate one core rendering function.
Renderings produced using field programmable gate array (FPGA) based prototypes are presented,
along with details of 90nm synthesised versions of the designs which show that close to an orderof-
magnitude speedup over a software implementation is possible. Due to the scalable nature of
the design, it is likely that any advantage can be maintained in the face of improving processor
speeds.
Significantly, due to the brute-force approach adopted, it is possible to eliminate an often-used
software acceleration method. This means that the device can interface almost directly to a frontend
modelling package, minimising much of the pre-processing required by most other proposals
QuickCSG: Fast Arbitrary Boolean Combinations of N Solids
QuickCSG computes the result for general N-polyhedron boolean expressions
without an intermediate tree of solids. We propose a vertex-centric view of the
problem, which simplifies the identification of final geometric contributions,
and facilitates its spatial decomposition. The problem is then cast in a single
KD-tree exploration, geared toward the result by early pruning of any region of
space not contributing to the final surface. We assume strong regularity
properties on the input meshes and that they are in general position. This
simplifying assumption, in combination with our vertex-centric approach,
improves the speed of the approach. Complemented with a task-stealing
parallelization, the algorithm achieves breakthrough performance, one to two
orders of magnitude speedups with respect to state-of-the-art CPU algorithms,
on boolean operations over two to dozens of polyhedra. The algorithm also
outperforms GPU implementations with approximate discretizations, while
producing an output without redundant facets. Despite the restrictive
assumptions on the input, we show the usefulness of QuickCSG for applications
with large CSG problems and strong temporal constraints, e.g. modeling for 3D
printers, reconstruction from visual hulls and collision detection
Doctor of Philosophy
dissertationThis dissertation explores three key facets of software algorithms for custom hardware ray tracing: primitive intersection, shading, and acceleration structure construction. For the first, primitive intersection, we show how nearly all of the existing direct three-dimensional (3D) ray-triangle intersection tests are mathematically equivalent. Based on this, a genetic algorithm can automatically tune a ray-triangle intersection test for maximum speed on a particular architecture. We also analyze the components of the intersection test to determine how much floating point precision is required and design a numerically robust intersection algorithm. Next, for shading, we deconstruct Perlin noise into its basic parts and show how these can be modified to produce a gradient noise algorithm that improves the visual appearance. This improved algorithm serves as the basis for a hardware noise unit. Lastly, we show how an existing bounding volume hierarchy can be postprocessed using tree rotations to further reduce the expected cost to traverse a ray through it. This postprocessing also serves as the basis for an efficient update algorithm for animated geometry. Together, these contributions should improve the efficiency of both software- and hardware-based ray tracers
QuickCSG: Fast Arbitrary Boolean Combinations of N Solids
QuickCSG computes the result for general N-polyhedron boolean expressions
without an intermediate tree of solids. We propose a vertex-centric view of the
problem, which simplifies the identification of final geometric contributions,
and facilitates its spatial decomposition. The problem is then cast in a single
KD-tree exploration, geared toward the result by early pruning of any region of
space not contributing to the final surface. We assume strong regularity
properties on the input meshes and that they are in general position. This
simplifying assumption, in combination with our vertex-centric approach,
improves the speed of the approach. Complemented with a task-stealing
parallelization, the algorithm achieves breakthrough performance, one to two
orders of magnitude speedups with respect to state-of-the-art CPU algorithms,
on boolean operations over two to dozens of polyhedra. The algorithm also
outperforms GPU implementations with approximate discretizations, while
producing an output without redundant facets. Despite the restrictive
assumptions on the input, we show the usefulness of QuickCSG for applications
with large CSG problems and strong temporal constraints, e.g. modeling for 3D
printers, reconstruction from visual hulls and collision detection
Developing serious games for cultural heritage: a state-of-the-art review
Although the widespread use of gaming for leisure purposes has been well documented, the use of games to support cultural heritage purposes, such as historical teaching and learning, or for enhancing museum visits, has been less well considered. The state-of-the-art in serious game technology is identical to that of the state-of-the-art in entertainment games technology. As a result, the field of serious heritage games concerns itself with recent advances in computer games, real-time computer graphics, virtual and augmented reality and artificial intelligence. On the other hand, the main strengths of serious gaming applications may be generalised as being in the areas of communication, visual expression of information, collaboration mechanisms, interactivity and entertainment. In this report, we will focus on the state-of-the-art with respect to the theories, methods and technologies used in serious heritage games. We provide an overview of existing literature of relevance to the domain, discuss the strengths and weaknesses of the described methods and point out unsolved problems and challenges. In addition, several case studies illustrating the application of methods and technologies used in cultural heritage are presented
Image Sampling with Quasicrystals
We investigate the use of quasicrystals in image sampling. Quasicrystals
produce space-filling, non-periodic point sets that are uniformly discrete and
relatively dense, thereby ensuring the sample sites are evenly spread out
throughout the sampled image. Their self-similar structure can be attractive
for creating sampling patterns endowed with a decorative symmetry. We present a
brief general overview of the algebraic theory of cut-and-project quasicrystals
based on the geometry of the golden ratio. To assess the practical utility of
quasicrystal sampling, we evaluate the visual effects of a variety of
non-adaptive image sampling strategies on photorealistic image reconstruction
and non-photorealistic image rendering used in multiresolution image
representations. For computer visualization of point sets used in image
sampling, we introduce a mosaic rendering technique.Comment: For a full resolution version of this paper, along with supplementary
materials, please visit at
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