Processing and interactive editing of huge point clouds from 3D scanners

This paper describes a new out-of-core multi-resolution data structure for real-time visualization, interactive editing and externally efficient processing of large point clouds. We describe an editing system that makes use of the novel data structure to provide interactive editing and preprocessing tools for large scanner data sets. Using the new data structure, we provide a complete tool chain for 3D scanner data processing, from data preprocessing and filtering to manual touch-up and real-time visualization. In particular, we describe an out-of-core outlier removal and bilateral geometry filtering algorithm, a toolset for interactive selection, painting, transformation, and filtering of huge out-of-core point-cloud data sets and a real-time rendering algorithm, which all use the same data structure as storage backend. The interactive tools work in real-time for small model modifications. For large scale editing operations, we employ a two-resolution approach where editing is planned in real-time and executed in an externally efficient offline computation afterwards. We evaluate our implementation on example data sets of sizes up to 63 GB, demonstrating that the proposed technique can be used effectively in real-world applications.     

Byte code level cross-compilation for developing web applications

JavaScript provides the technological foundation of Web 2.0 applications. AJAX (Asynchronous JavaScript And XML) applications have received wide-spread attention as a new way to develop highly interactive web applications. Breaking with the complete-page-reload paradigm of traditional web applications, AJAX applications rival desktop applications in their look-and-feel. But AJAX places a high burden on a web developer requiring extensive JavaScript knowledge as well as other advanced client-side technologies. In this paper, we introduce a technique that allows a developer to implement an application in Java or any.NET language and then automatically cross-compile it to an AJAX-enabled web application.     

Self-consistent gradient flow for shape optimization

We present a model for image segmentation and describe a gradient-descent method for level-set based shape optimization. It is commonly known that gradient-descent methods converge slowly due to zig–zag movement. This can also be observed for our problem, especially when sharp edges are present in the image. We interpret this in our specific context to gain a better understanding of the involved difficulties. One way to overcome slow convergence is the use of second-order methods. For our situation, they require derivatives of the potentially noisy image data and are thus undesirable. Hence, we propose a new method that can be interpreted as a self-consistent gradient flow and does not need any derivatives of the image data. It works very well in practice and leads to a far more efficient optimization algorithm. A related idea can also be used to describe the mean-curvature flow of a mean-convex surface. For this, we formulate a mean-curvature Eikonal equation, which allows a numerical propagation of the mean-curvature flow of a surface without explicit time stepping.     

Light scattering from filaments

Photorealistic visualization of a huge number of individual filaments like in the case of hair, fur, or knitwear is a challenging task: Explicit rendering approaches for simulating radiance transfer at a filament get totally impracticable with respect to rendering performance and it is also not obvious how to derive efficient scattering functions for different levels of (geometric) abstraction or how to deal with very complex scattering mechanisms. We present a novel uniform formalism for light scattering from filaments in terms of radiance, which we call the bidirectional fiber scattering distribution function (BFSDF). We show that previous specialized approaches, which have been developed in the context of hair rendering, can be seen as instances of the BFSDF. Similar to the role of the BSSRDF for surface scattering functions, the BFSDF can be seen as a general approach for light scattering from filaments, which is suitable for deriving approximations in a canonic and systematic way. For the frequent cases of distant light sources and observers, we deduce an efficient far field approximation (bidirectional curve scattering distribution function, BCSDF). We show that on the basis of the BFSDF, parameters for common rendering techniques can be estimated in a non-ad-hoc, but physically-based way     

Theoretical and Experimental Damage Prediction in Cold and Semi‐Hot Bulk Forming of Ductile Steels

Bulk forging is among the most important manufacturing methods in metal forming, due to its wide applicability from some ounces to several tons of steel in a high diversity of shapes and forming conditions. Economical constraints demand for further optimisation and cost‐effective production. This requires the application of suitable finite elements simulation software, in order to support the already digitalised construction processes. Ductile damage is one of the most severe problems to arise during the production sequences, not only in cold but also in semi‐hot forging operations. Mathematical approaches exist for the modelling and simulation of ductile fracture in steel. In this paper some widespread used damage models are introduced and discussed. Their damage prediction quality has been verified by experiments, the tensile test and the collar specimen upsetting with several different steels under cold and semi‐hot forging conditions. The methods for the experimental fracture detection are introduced as well. In cold forging the passive ultrasonic testing with integrated statistical filtering algorithms is used. As this method is not applicable to semi‐hot forging experiments, optical fracture detection by means of a high‐speed camera is used instead. A very interesting material behaviour of the steels tested has been identified in the semi‐hot upsetting of collar specimen. For every steel a distinct temperature crossover interval exists, in which the forging process abruptly changes from damaged to undamaged state. This interval amounts to some degrees Celsius only for each of the seven materials investigated. Among the damage models proposed, the Model of Effective Stresses by Lemaitre is chosen for the application to a cold and a semi‐hot forging operation. These industrial processes of an axle end (cold) and a journal bearing (semi‐hot) are susceptible to damage for reasons to be discussed in this paper. It will be shown that the internal fracture of the axle end (chevrons) and the surface fissures of the journal bearing can be predicted with high accuracy. Moreover, the application of the damage model in the finite element software MSC.SuperForm 2004 offers a promising approach for process optimisation. Several possibilities could be tested for their suitability of reducing the calculated damage: geometry variation of the forming tools, process annealing, different materials. The use of damage models in finite element simulation can be regarded as a further step towards an optimal process design.     

Aufbau einer Versuchsanlage zur katalytischen Spaltung des 9,10‐Dihydroxystearinsäuremethylesters mit Luftsauerstoff

The development of new catalysts for the oxidation of chemical compounds with oxygen as cheap and environmentally oxidant is an important topic of the current research. Due to the risk of the formation of potentially explosive gas mixtures aerobic oxidation reactions have to be performed with consideration of the explosion prevention. A safety concept for aerobic oxidation reactions and the construction of an experimental plant is presented. The oxidative cleavage of methyl 9,10‐dihydroxystearate to azelaic acid methyl ester and pelargonic acid was investigated as a model reaction.     

System-specific static code analyses: a case study in the complex embedded systems domain

In this paper, we are exploring the approach to utilize system-specific static analyses of code with the goal to improve software quality for specific software systems. Specialized analyses, tailored for a particular system, make it possible to take advantage of system/domain knowledge that is not available to more generic analyses. Furthermore, analyses can be selected and/or developed in order to best meet the challenges and specific issues of the system at hand. As a result, such analyses can be used as a complement to more generic code analysis tools because they are likely to have a better impact on (business) concerns such as improving certain software quality attributes and reducing certain classes of failures. We present a case study of a large, industrial embedded system, giving examples of what kinds of analyses could be realized and demonstrate the feasibility of implementing such analyses. We synthesize lessons learned based on our case study and provide recommendations on how to realize system-specific analyses and how to get them adopted by industry.     

Fracture Toughness of Advanced Structural Ceramics: Applying ASTM C1421

The three methods of determining the quasi‐static Mode I fracture toughness (K_Ic) (surface crack in flexure—SC, single‐edge precracked beam—PB, and chevron‐notched beam—VB) found in ASTM C1421 were applied to a variety of advanced ceramic materials. All three methods produced valid and comparable K_Ic values for the Al₂O₃, SiC, Si₃N₄, and SiAlON ceramics examined. However, not all methods could successfully be applied to B₄C, ZrO₂, and WC ceramics due to a variety of material factors. The coarse‐grained microstructure of one B₄C hindered the ability to observe and measure the precracks generated in the SC and PB methods while the transformation toughening in the ZrO₂ prevented the formation of the SC and PB precracks and thus made it impossible to use either method on this ceramic. The high strength and elastic modulus of the WC made it impossible to achieve stable crack growth using the VB method because the specimen stored a tremendous amount of energy prior to fracture. Even though these methods have passed the rigors of the standardization process there are still some issues to be resolved when the methods are applied to certain classes of ceramics. It is recommended that, when appropriate, at least two of these methods be employed to determine the K_Ic, especially when a new or unfamiliar ceramic is being evaluated.