1,655 research outputs found
Renormalization techniques for quantum spin systems. Ground-state energies
Projection of the Hamiltonian of an antiferromagnetic lattice of spins , without external fields, onto a subspace of the total spinor space gives an approximation for the lowest eigenvalue of this Hamiltonian. Repeated projection results in a series expansion for this approximation. In each projection the form of the Hamiltonian is conserved. The formal structure of this projection technique shows a strong analogy with the Wilson theory or renormalization-group theory of phase transitions. Numerical results are given for linear chains and triangular lattice
A -adic RanSaC algorithm for stereo vision using Hensel lifting
A -adic variation of the Ran(dom) Sa(mple) C(onsensus) method for solving
the relative pose problem in stereo vision is developped. From two 2-adically
encoded images a random sample of five pairs of corresponding points is taken,
and the equations for the essential matrix are solved by lifting solutions
modulo 2 to the 2-adic integers. A recently devised -adic hierarchical
classification algorithm imitating the known LBG quantisation method classifies
the solutions for all the samples after having determined the number of
clusters using the known intra-inter validity of clusterings. In the successful
case, a cluster ranking will determine the cluster containing a 2-adic
approximation to the "true" solution of the problem.Comment: 15 pages; typos removed, abstract changed, computation error remove
3D exemplar-based image inpainting in electron microscopy
In electron microscopy (EM) a common problem is the non-availability of data, which causes artefacts in reconstructions. In this thesis the goal is to generate artificial data where missing in EM by using exemplar-based inpainting (EBI). We implement an accelerated 3D version tailored to applications in EM, which reduces reconstruction times from days to minutes. We develop intelligent sampling strategies to find optimal data as input for reconstruction methods. Further, we investigate approaches to reduce electron dose and acquisition time. Sparse sampling followed by inpainting is the most promising approach. As common evaluation measures may lead to misinterpretation of results in EM and falsify a subsequent analysis, we propose to use application driven metrics and demonstrate this in a segmentation task. A further application of our technique is the artificial generation of projections in tiltbased EM. EBI is used to generate missing projections, such that the full angular range is covered. Subsequent reconstructions are significantly enhanced in terms of resolution, which facilitates further analysis of samples. In conclusion, EBI proves promising when used as an additional data generation step to tackle the non-availability of data in EM, which is evaluated in selected applications. Enhancing adaptive sampling methods and refining EBI, especially considering the mutual influence, promotes higher throughput in EM using less electron dose while not lessening quality.Ein häufig vorkommendes Problem in der Elektronenmikroskopie (EM) ist die Nichtverfügbarkeit von Daten, was zu Artefakten in Rekonstruktionen führt. In dieser Arbeit ist es das Ziel fehlende Daten in der EM künstlich zu erzeugen, was durch Exemplar-basiertes Inpainting (EBI) realisiert wird. Wir implementieren eine auf EM zugeschnittene beschleunigte 3D Version, welche es ermöglicht, Rekonstruktionszeiten von Tagen auf Minuten zu reduzieren. Wir entwickeln intelligente Abtaststrategien, um optimale Datenpunkte für die Rekonstruktion zu erhalten. Ansätze zur Reduzierung von Elektronendosis und Aufnahmezeit werden untersucht. Unterabtastung gefolgt von Inpainting führt zu den besten Resultaten. Evaluationsmaße zur Beurteilung der Rekonstruktionsqualität helfen in der EM oft nicht und können zu falschen Schlüssen führen, weswegen anwendungsbasierte Metriken die bessere Wahl darstellen. Dies demonstrieren wir anhand eines Beispiels. Die künstliche Erzeugung von Projektionen in der neigungsbasierten Elektronentomographie ist eine weitere Anwendung. EBI wird verwendet um fehlende Projektionen zu generieren. Daraus resultierende Rekonstruktionen weisen eine deutlich erhöhte Auflösung auf. EBI ist ein vielversprechender Ansatz, um nicht verfügbare Daten in der EM zu generieren. Dies wird auf Basis verschiedener Anwendungen gezeigt und evaluiert. Adaptive Aufnahmestrategien und EBI können also zu einem höheren Durchsatz in der EM führen, ohne die Bildqualität merklich zu verschlechtern
Automatic segmentation and reconstruction of traffic accident scenarios from mobile laser scanning data
Virtual reconstruction of historic sites, planning of restorations and attachments of new building parts, as well as forest inventory are few examples of fields that benefit from the application of 3D surveying data. Originally using 2D photo based documentation and manual distance measurements, the 3D information obtained from multi camera and laser scanning systems realizes a noticeable improvement regarding the surveying times and the amount of generated 3D information. The 3D data allows a detailed post processing and better visualization of all relevant spatial information. Yet, for the extraction of the required information from the raw scan data and for the generation of useable visual output, time-consuming, complex user-based data processing is still required, using the commercially available 3D software tools.
In this context, the automatic object recognition from 3D point cloud and depth data has been discussed in many different works. The developed tools and methods however, usually only focus on a certain kind of object or the detection of learned invariant surface shapes. Although the resulting methods are applicable for certain practices of data segmentation, they are not necessarily suitable for arbitrary tasks due to the varying requirements of the different fields of research.
This thesis presents a more widespread solution for automatic scene reconstruction from 3D point clouds, targeting street scenarios, specifically for the task of traffic accident scene analysis and documentation. The data, obtained by sampling the scene using a mobile scanning system is evaluated, segmented, and finally used to generate detailed 3D information of the scanned environment.
To realize this aim, this work adapts and validates various existing approaches on laser scan segmentation regarding the application on accident relevant scene information, including road surfaces and markings, vehicles, walls, trees and other salient objects. The approaches are therefore evaluated regarding their suitability and limitations for the given tasks, as well as for possibilities concerning the combined application together with other procedures. The obtained knowledge is used for the development of new algorithms and procedures to allow a satisfying segmentation and reconstruction of the scene, corresponding to the available sampling densities and precisions.
Besides the segmentation of the point cloud data, this thesis presents different visualization and reconstruction methods to achieve a wider range of possible applications of the developed system for data export and utilization in different third party software tools
Acceleration Techniques for Photo Realistic Computer Generated Integral Images
The research work presented in this thesis has approached the task of accelerating the
generation of photo-realistic integral images produced by integral ray tracing.
Ray tracing algorithm is a computationally exhaustive algorithm, which spawns one ray
or more through each pixel of the pixels forming the image, into the space containing
the scene. Ray tracing integral images consumes more processing time than normal
images. The unique characteristics of the 3D integral camera model has been analysed
and it has been shown that different coherency aspects than normal ray tracing can be
investigated in order to accelerate the generation of photo-realistic integral images.
The image-space coherence has been analysed describing the relation between rays and
projected shadows in the scene rendered. Shadow cache algorithm has been adapted in
order to minimise shadow intersection tests in integral ray tracing. Shadow intersection
tests make the majority of the intersection tests in ray tracing. Novel pixel-tracing
styles are developed uniquely for integral ray tracing to improve the image-space
coherence and the performance of the shadow cache algorithm. Acceleration of the
photo-realistic integral images generation using the image-space coherence information
between shadows and rays in integral ray tracing has been achieved with up to 41 % of
time saving. Also, it has been proven that applying the new styles of pixel-tracing does
not affect of the scalability of integral ray tracing running over parallel computers.
The novel integral reprojection algorithm has been developed uniquely through
geometrical analysis of the generation of integral image in order to use the tempo-spatial
coherence information within the integral frames. A new derivation of integral
projection matrix for projecting points through an axial model of a lenticular lens has
been established. Rapid generation of 3D photo-realistic integral frames has been
achieved with a speed four times faster than the normal generation
A code excited linear predictive coder: using a moments algorithm
A speech coding algorithm was developed which was based on a new method of selecting the excitation signal from a codebook of residual error sequences. The residual error sequences in the codebook were generated from 512 frames of real speech signals. L.P.C. inverse filtering was used to obtain the residual signal.
Each residual error signal was assigned an index. The index was generated using a moments algorithm. These indices were stored on a Graded Binary Tree. A Binary Search was then used to select the correct index. The use of a Graded Binary Tree in the coding algorithm reduced the search time.
The algorithm faithfully reproduced the original speech when the test residual error signal was chosen from the training data. When the test residual error signal was outside the training data, synthetic speech of a recognisable quality was produced.
Finally, the fundamentals of speech coders are discussed in detail and various developments are suggested
VISIO-HAPTIC DEFORMABLE MODEL FOR HAPTIC DOMINANT PALPATION SIMULATOR
Vision and haptic are two most important modalities in a medical simulation. While
visual cues assist one to see his actions when performing a medical procedure, haptic
cues enable feeling the object being manipulated during the interaction. Despite their
importance in a computer simulation, the combination of both modalities has not been
adequately assessed, especially that in a haptic dominant environment. Thus, resulting
in poor emphasis in resource allocation management in terms of effort spent in
rendering the two modalities for simulators with realistic real-time interactions.
Addressing this problem requires an investigation on whether a single modality
(haptic) or a combination of both visual and haptic could be better for learning skills
in a haptic dominant environment such as in a palpation simulator. However, before
such an investigation could take place one main technical implementation issue in
visio-haptic rendering needs to be addresse
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