Two‐Level Grids for Ray Tracing on GPUs

We investigate the use of two‐level nested grids as acceleration structure for ray tracing of dynamic scenes. We propose a massively parallel, sort‐based construction algorithm and show that the two‐level grid is one of the structures that is fastest to construct on modern graphics processors. The structure handles non‐uniform primitive distributions more robustly than the uniform grid and its traversal performance is comparable to those of other high quality acceleration structures used for dynamic scenes. We propose a cost model to determine the grid resolution and improve SIMD utilization during ray‐triangle intersection by employing a hybrid packetization strategy. The build times and ray traversal acceleration provide overall rendering performance superior to previous approaches for real time rendering of animated scenes on GPUs.     

Assessing the performance of a spectral reflectance estimation method based on a diffraction grating and a spectroradiometer

Constant improvements in digital cameras have made it possible to use these devices for colour acquisition and reproduction at an advanced level. It is known that a colour match for all observers when changing illumination can only be achieved by matching spectral data. Obtaining spectral data from digital camera RGB values could provide a new way of using the digital camera as a spectrophotometric tool or as a high‐quality colour‐capturing system that is required in more demanding applications. In the present study, two spectral reflectance estimation methods were examined – the Imai–Berns method (ImaiBerns) and the spectral‐sensitivity‐based method (SpecSens). The purpose of the research was to simplify the procedure of the SpecSens method by using a diffraction grating and a spectroradiometer instead of a monochromator, and to compare the results with those of the ImaiBerns approach. Obtained spectral reflectance estimates were evaluated using the root‐mean‐square error and ?E₀₀ metrics. Results of the research show that the ImaiBerns method was superior to SpecSens, most likely because the former method does not require knowledge of the camera spectral sensitivities, which often introduces errors into reflectance estimation calculations. Both methods were successful in predicting black, brownish, and dark patches, as indicated by a low root‐mean‐square error, as well as unsaturated pastel, pink, or skin colours, which produced low ?E₀₀ values. On the other hand, many of the patches with a low root‐mean‐square error also exhibited high ?E₀₀ values, while bright, nearly‐white patches were characterised by a high root‐mean‐square error.     

Technostress aus einer neurobiologischen Perspektive

Despite the positive impact of information and communication technology (ICT) on an individual, organizational, and societal level (e.g., increased access to information, as well as enhanced performance and productivity), both scientific research and anecdotal evidence indicate that human-machine interaction, both in a private and organizational context, may lead to notable stress perceptions in users. This type of stress is referred to as technostress. A review of the literature shows that most studies used questionnaires to investigate the nature, antecedents, and consequences of technostress. Despite the value of the vast amount of questionnaire-based technostress research, we draw upon a different conceptual perspective, namely neurobiology. Specifically, we report on a laboratory experiment in which we investigated the effects of system breakdown on changes in users?? levels of cortisol, which is a major stress hormone in humans. The results of our study show that cortisol levels increase significantly as a consequence of system breakdown in a human-computer interaction task. In demonstrating this effect, our study has major implications for ICT research, development, management, and health policy. We confirm the value of a category of research heretofore largely neglected in ICT-related disciplines (particularly in business and information systems engineering, BISE, as well as information systems research, ISR), and argue that future research investigating human-machine interactions should consider the neurobiological perspective as a valuable complement to traditional concepts.     

GPU Ray Tracing using Irregular Grids

We present a spatial index structure to accelerate ray tracing on GPUs. It is a flat, non‐hierarchical spatial subdivision of the scene into axis aligned cells of varying size. In order to construct it, we first nest an octree into each cell of a uniform grid. We then apply two optimization passes to increase ray traversal performance: First, we reduce the expected cost for ray traversal by merging cells together. This adapts the structure to complex primitive distributions, solving the “teapot in a stadium” problem. Second, we decouple the cell boundaries used during traversal for rays entering and exiting a given cell. This allows us to extend the exiting boundaries over adjacent cells that are either empty or do not contain additional primitives. Now, exiting rays can skip empty space and avoid repeating intersection tests. Finally, we demonstrate that in addition to the fast ray traversal performance, the structure can be rebuilt efficiently in parallel, allowing for ray tracing dynamic scenes.     

String‐Based Synthesis of Structured Shapes

We propose a novel method to synthesize geometric models from a given class of context‐aware structured shapes such as buildings and other man‐made objects. The central idea is to leverage powerful machine learning methods from the area of natural language processing for this task. To this end, we propose a technique that maps shapes to strings and vice versa, through an intermediate shape graph representation. We then convert procedurally generated shape repositories into text databases that, in turn, can be used to train a variational autoencoder. The autoencoder enables higher level shape manipulation and synthesis like, for example, interpolation and sampling via its continuous latent space. We provide project code and pre‐trained models.     

Damage classification of concrete structures. The state of the art report of RILEM Technical Committee 104-DCC activity

Resume Le comportementin situ des constructions en béton permet de déterminer leur état et leur durée de service. Il est essentiel de recommander les méthodes les meilleures et les plus économiques pour le diagnostic et la vérification des défauts, détériorations, réseaux de fissures, de la corrosion et d’autres caractéristiques du comportementin situ des constructions en béton de types et d’ages différents. Il conviendrait d’établir une relation entre les méthodes d’essai unifiées et la classification des dommages qui dépend des normes d’études, des méthodes de calcul, de la qualité des matériaux et de la technologie de la construction comme de l’influence de l’environnement sur le comportement, la durabilité et la longévité des structures.

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The papers published in this issue following the activity report of 104-DCC Committee drafted by Dr Javor are related to different aspects of the work of the Committee to be presented at the Bratislava Symposium which will be held on September 2–6, 1991. Discussion of the papers would be welcomed.     

Dual polarisation of microstrip reflectarray antenna

Dual polarisation of a microstrip reflectarray was demonstrated for the first time. A 16 element array of square microstrip patch antennas operating in the X-band was used to reflect the main beam 20" off broadside in both the E-plane and H-plane