3,148 research outputs found
Sensor system and related models to determine irregular shaped 3-D objects
This work comprises several parts, the initial part o f which is a review o f the techniques
in use at present for measuring shape and characterising products. The major work
details a ring sensor system, which consists o f a large number o f transmitters and
receivers alternately arranged on the circumference o f a metal annulus. Using a modified
polar co-ordinate system and trigonometric functions, two enveloping spirals o f an
object can be determined. One or both spirals can then be used for further data analysis.
Each spiral consists o f intersections between enveloping chords and parts o f the chords.
The area surrounding the object is segmented and properties such as volume and axis
measurements can be determined. A mode! was developed to simulate artificial objects
o f various shapes. Simulation tests were carried out to determine the limits o f the system
concerning position within the ring, shape and speed o f the object and resolution o f the
ring. A ring was manufactured for actual tests, which were carried out mainly on
potatoes to confirm the possible use in practice and to show the relative merits compared
with existing systems. Interesting side issues are introduced, such as the low number of
primary data, possibilities of further reduction using differential coding, and the
consumption time of the algorithms. Finally, a model for the simulation o f more than
one object in the ring at the same time is introduced and a possible way o f separation is
investigated
Doctor of Philosophy
dissertationWhile boundary representations, such as nonuniform rational B-spline (NURBS) surfaces, have traditionally well served the needs of the modeling community, they have not seen widespread adoption among the wider engineering discipline. There is a common perception that NURBS are slow to evaluate and complex to implement. Whereas computer-aided design commonly deals with surfaces, the engineering community must deal with materials that have thickness. Traditional visualization techniques have avoided NURBS, and there has been little cross-talk between the rich spline approximation community and the larger engineering field. Recently there has been a strong desire to marry the modeling and analysis phases of the iterative design cycle, be it in car design, turbulent flow simulation around an airfoil, or lighting design. Research has demonstrated that employing a single representation throughout the cycle has key advantages. Furthermore, novel manufacturing techniques employing heterogeneous materials require the introduction of volumetric modeling representations. There is little question that fields such as scientific visualization and mechanical engineering could benefit from the powerful approximation properties of splines. In this dissertation, we remove several hurdles to the application of NURBS to problems in engineering and demonstrate how their unique properties can be leveraged to solve problems of interest
Lazy visibility evaluation for exact soft shadows
PrĂ©sentation invitĂ©e de l'article du mĂȘme nom publiĂ© en 2012 dans la revue Computer Graphics Forum.International audienceThis paper presents a novel approach to compute high quality and noise-free soft shadows using exact visibility computations. This work relies on a theoretical framework allowing to group lines according to the geometry they intersect. From this study, we derive a new algorithm encoding lazily the visibility from a polygon. Contrary to previous works on from-polygon visibility, our approach is very robust and straightforward to implement. We apply this algorithm to solve exactly and efficiently the visibility of an area light source from any point in a scene. As a consequence, results are not sensitive to noise, contrary to soft shadows methods based on area light source sampling. We demonstrate the reliability of our approach on different scenes and configurations
Appearance Preserving Rendering of Out-of-Core Polygon and NURBS Models
In Computer Aided Design (CAD) trimmed NURBS surfaces are widely used due to their flexibility. For rendering and simulation however, piecewise linear representations of these objects are required. A relatively new field in CAD is the analysis of long-term strain tests. After such a test the object is scanned with a 3d laser scanner for further processing on a PC. In all these areas of CAD the number of primitives as well as their complexity has grown constantly in the recent years. This growth is exceeding the increase of processor speed and memory size by far and posing the need for fast out-of-core algorithms. This thesis describes a processing pipeline from the input data in the form of triangular or trimmed NURBS models until the interactive rendering of these models at high visual quality. After discussing the motivation for this work and introducing basic concepts on complex polygon and NURBS models, the second part of this thesis starts with a review of existing simplification and tessellation algorithms. Additionally, an improved stitching algorithm to generate a consistent model after tessellation of a trimmed NURBS model is presented. Since surfaces need to be modified interactively during the design phase, a novel trimmed NURBS rendering algorithm is presented. This algorithm removes the bottleneck of generating and transmitting a new tessellation to the graphics card after each modification of a surface by evaluating and trimming the surface on the GPU. To achieve high visual quality, the appearance of a surface can be preserved using texture mapping. Therefore, a texture mapping algorithm for trimmed NURBS surfaces is presented. To reduce the memory requirements for the textures, the algorithm is modified to generate compressed normal maps to preserve the shading of the original surface. Since texturing is only possible, when a parametric mapping of the surface - requiring additional memory - is available, a new simplification and tessellation error measure is introduced that preserves the appearance of the original surface by controlling the deviation of normal vectors. The preservation of normals and possibly other surface attributes allows interactive visualization for quality control applications (e.g. isophotes and reflection lines). In the last part out-of-core techniques for processing and rendering of gigabyte-sized polygonal and trimmed NURBS models are presented. Then the modifications necessary to support streaming of simplified geometry from a central server are discussed and finally and LOD selection algorithm to support interactive rendering of hard and soft shadows is described
An Unsupervised Method for Estimating the Global Horizontal Irradiance from Photovoltaic Power Measurements
In this paper, we present a method to determine the global horizontal
irradiance (GHI) from the power measurements of one or more PV systems, located
in the same neighborhood. The method is completely unsupervised and is based on
a physical model of a PV plant. The precise assessment of solar irradiance is
pivotal for the forecast of the electric power generated by photovoltaic (PV)
plants. However, on-ground measurements are expensive and are generally not
performed for small and medium-sized PV plants. Satellite-based services
represent a valid alternative to on site measurements, but their space-time
resolution is limited. Results from two case studies located in Switzerland are
presented. The performance of the proposed method at assessing GHI is compared
with that of free and commercial satellite services. Our results show that the
presented method is generally better than satellite-based services, especially
at high temporal resolutions
Shadow Techniques for Interactive and Real-Time Applications
Shadows provide important visual cues for the relative position of objects in threedimensional space. For interactive and real-time applications, e.g. in virtual reality systems or games, the shadow computation needs to be extremely fast, usually synchronized with the displays refresh rate. Using dynamic scenes with many, movable light sources, shadow computation is therefore often the main bottleneck in a rendering system. In this thesis we will discuss this problem in detail: Originating from Williams shadow maps and Crows shadow volumes, we will present hardware accelerated shadow techniques that are able to generate shadows of high-quality while still being fast enough to be used in real-time or interactive applications. We will show algorithms for the computation of hard shadows as well as for the more complex problem of approximating soft shadows caused by area light sources.Schatten sind wichtige visuelle Merkmale die ĂŒber die relative Position eines Objektes in einem drei-dimensionalen Raum Aufschluss geben. Die Schattenberechnung muss fĂŒr interaktive und Echtzeit-Anwendungen, wie z.B. Virtual Reality Systeme oder in Spielen, extrem schnell erfolgen, idealerweise synchronisiert mit der Bildwiederholfrequenz. Im Fall von dynamischen Szenen mit vielen, beweglichen Lichtquellen, ist die Berechnung von Schatten oftmals der zeitkritischste Teil innerhalb eines Rendering-Systems.
In dieser Dissertation behandeln wir genau dieses Problem im Detail. Ausgehend
vonWilliams\u27; Shadow Maps und Crow\u27;s Shadow Volumes werden Hardwarebeschleunigte
Schattentechniken vorgestellt, die Schatten von hoher QualitÀt erzeugen
können, aber trotzdem so effizient sind, dass sie fĂŒr Echtzeit- und interaktive
Anwendungen eingesetzt werden können. Wir werden sowohl Algorithmen zur
Berechnung harter Schatten beschreiben, als auch das schwierigere Problem der
Approximation von sanften Schatten, wie sie z.B. bei FlÀchenlichtquellen entstehen, behandeln
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Real-time spatial modeling to detect and track resources on construction sites
For more than 10 years the U.S. construction industry has experienced over 1,000
fatalities annually. Many fatalities may have been prevented had the individuals and
equipment involved been more aware of and alert to the physical state of the environment
around them. Awareness may be improved by automatic 3D (three-dimensional) sensing
and modeling of the job site environment in real-time. Existing 3D modeling approaches
based on range scanning techniques are capable of modeling static objects only, and thus
cannot model in real-time dynamic objects in an environment comprised of moving
humans, equipment, and materials. Emerging prototype 3D video range cameras offer
another alternative by facilitating affordable, wide field of view, automated static and
dynamic object detection and tracking at frame rates better than 1Hz (real-time).
This dissertation presents an imperical work and methodology to rapidly create a
spatial model of construction sites and in particular to detect, model, and track the position, dimension, direction, and velocity of static and moving project resources in real-time, based on range data obtained from a three-dimensional video range camera in a
static or moving position. Existing construction site 3D modeling approaches based on
optical range sensing technologies (laser scanners, rangefinders, etc.) and 3D modeling
approaches (dense, sparse, etc.) that offered potential solutions for this research are
reviewed. The choice of an emerging sensing tool and preliminary experiments with this
prototype sensing technology are discussed. These findings led to the development of a
range data processing algorithm based on three-dimensional occupancy grids which is
demonstrated in detail. Testing and validation of the proposed algorithms have been
conducted to quantify the performance of sensor and algorithm through extensive
experimentation involving static and moving objects. Experiments in indoor laboratory
and outdoor construction environments have been conducted with construction resources
such as humans, equipment, materials, or structures to verify the accuracy of the
occupancy grid modeling approach. Results show that modeling objects and measuring
their position, dimension, direction, and speed had an accuracy level compatible to the
requirements of active safety features for construction. Results demonstrate that video
rate 3D data acquisition and analysis of construction environments can support effective
detection, tracking, and convex hull modeling of objects. Exploiting rapidly generated
three-dimensional models for improved visualization, communications, and process
control has inherent value, broad application, and potential impact, e.g. as-built vs. as-planned comparison, condition assessment, maintenance, operations, and construction
activities control. In combination with effective management practices, this sensing
approach has the potential to assist equipment operators to avoid incidents that result in
reduce human injury, death, or collateral damage on construction sites.Civil, Architectural, and Environmental Engineerin
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