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"... Abstract: In modern production facilities industrial robots and humans are supposed to share a common working area. To avoid collisions, the distances between objects need to be measured conservatively, which can be done by a camera network. To estimate these distances, unmodelled objects, e.g. an i ..."
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Abstract: In modern production facilities industrial robots and humans are supposed to share a common working area. To avoid collisions, the distances between objects need to be measured conservatively, which can be done by a camera network. To estimate these distances, unmodelled objects, e.g. an interacting human, need to be modelled and distinguished from premodelled objects, like workbenches or robots, by image processing such as the background subtraction method. The quality of such an approach massively depends on the position and orientation of each camera. Of particular interest in this context is the error minimisation of the above mentioned distance determined by image processing. Here, we formulate this minimisation as an abstract optimisation problem. Moreover, we state various aspects on the implementation, e.g. reasons for the selection of a suitable optimisation method, analyse the complexity of the proposed method and present a basic version used for extensive experiments.
Optimal Camera Placement to measure Distances Conservativly Regarding Static and Dynamic Obstacles, preprint (2011). Available at http://arxiv.org/abs/1105.3270
"... Abstract—In modern production facilities industrial robots and humans are supposed to interact sharing a common working area. In order to avoid collisions, the distances between objects need to be measured conservatively which can be done by a camera network. To estimate the acquired distance, unmod ..."
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Abstract—In modern production facilities industrial robots and humans are supposed to interact sharing a common working area. In order to avoid collisions, the distances between objects need to be measured conservatively which can be done by a camera network. To estimate the acquired distance, unmodelled objects, e.g., an interacting human, need to be modelled and distinguished from premodelled objects like workbenches or robots by image processing such as the background subtraction method. The quality of such an approach massively depends on the settings of the camera network, that is the positions and orientations of the individual cameras. Of particular interest in this context is the minimization of the error of the distance using the objects modelled by the background subtraction method instead of the real objects. Here, we show how this minimization can be formulated as an abstract optimization problem. Moreover, we state various aspects on the implementation as well as reasons for the selection of a suitable optimization method, analyze the complexity of the proposed method and present a basic version used for extensive experiments. Index Terms—Closed range photogrammetry, optimization, camera network, camera placement, error minimization I.
Thickening Freeform Surfaces for Solid Fabrication
"... Purpose: Given an intersectionfree mesh surface S, we introduce a method to thicken S into a solid H located at one side of S. By such a surfacetosolid conversion operation, industrial users are able to fabricate a designed (or reconstructed) surface by rapid prototyping. Design/methodology/appro ..."
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Purpose: Given an intersectionfree mesh surface S, we introduce a method to thicken S into a solid H located at one side of S. By such a surfacetosolid conversion operation, industrial users are able to fabricate a designed (or reconstructed) surface by rapid prototyping. Design/methodology/approach: In this paper, we first investigate an implicit representation of the thickened solid H according to an extension of signed distance function. After that, a partial surface reconstruction algorithm is proposed to generate the boundary surface ∂H of H, which remains the given surface S on the resultant surface. Finding: Experimental tests show that the thickening results generated by our method give nearly uniform thickness and meanwhile do not present shape approximation error at the region of input surface S. These two good properties are important to the industrial applications of solid fabrication. Research limitation/implications: The input polygonal model is assumed to be intersectionfree, where models containing selfintersection will lead to invalid thickening results. Originality/value: A novel robust operation to convert a freeform open surface into a solid by introducing no shape approximation error. A new implicit function that gives a compact mathematical representation, which can easily handle the topological change on the thickened solids. A new polygonization algorithm that generates faces for the boundary of thickened solid meanwhile retaining faces on the input open mesh.
Summary on Several Key Techniques in 3D Geological Modeling
, 2014
"... Several key techniques in 3D geological modeling including planar mesh generation, spatial interpolation, and surface intersection are summarized in this paper. Note that these techniques are generic and widely used in various applications but play a key role in 3D geological modeling.There are two ..."
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Several key techniques in 3D geological modeling including planar mesh generation, spatial interpolation, and surface intersection are summarized in this paper. Note that these techniques are generic and widely used in various applications but play a key role in 3D geological modeling.There are two essential procedures in 3D geological modeling: the first is the simulation of geological interfaces using geometric surfaces and the second is the building of geological objects by means of various geometric computations such as the intersection of surfaces. Discrete geometric surfaces that represent geological interfaces can be generated by creating planar meshes first and then spatially interpolating; those surfaces intersect and then form volumes that represent threedimensional geological objects such as rock bodies. In this paper, the most commonly used algorithms of the key techniques in 3D geological modeling are summarized.
Masatomo Inui Quad Pillars and Delta Pillars: Algorithms for Converting Dexel Models to Polyhedral Models
"... In the geometric simulation of multiaxis milling, a dexel representation solid model is frequently used. In this modeling method, the object shape is defined as a collection of vertical segments (dexels) based on a twodimensional regular square grid in the XY plane. In this paper, the authors pro ..."
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In the geometric simulation of multiaxis milling, a dexel representation solid model is frequently used. In this modeling method, the object shape is defined as a collection of vertical segments (dexels) based on a twodimensional regular square grid in the XY plane. In this paper, the authors propose the quad pillars algorithm and its enhanced version named the delta pillars algorithm for converting a dexel model to an equivalent polyhedral stereolithography (STL) model. These algorithms define a series of vertical pillar shapes for each square cell of the grid to represent the object shape as a bundle of pillars. The final polyhedral model is obtained by performing a simplified Boolean union operation of the pillar shapes. Unlike prior methods, the proposed algorithms are simple and fast and are guaranteed to generate a watertight polyhedral model without holes, gaps, or Tjunctions. An experimental system is implemented and conversion tests are performed. The system converted a dexel model based on a highresolution grid to a polyhedral model in a practical amount of time.
About the Lecturers
"... Animating detailed liquid surfaces has continually been a challenge for computer graphics researchers and visual effects artists. Over the past few years, a strong trend has emerged among researchers in this field towards meshbased surface tracking in order to synthesize extremely detailed liquid s ..."
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Animating detailed liquid surfaces has continually been a challenge for computer graphics researchers and visual effects artists. Over the past few years, a strong trend has emerged among researchers in this field towards meshbased surface tracking in order to synthesize extremely detailed liquid surfaces as efficiently as possible. This course will provide attendees with a solid understanding of the steps necessary to create a fluid simulator with a meshbased liquid surface. The course will begin with an overview of several existing liquid surface tracking techniques, discussing the pros and cons of each method. We will then provide instructions and a simple demonstration on how to embed a triangle mesh into a finitedifferencebased fluid simulator. Once this groundwork has been laid, the next section of the course will stress the importance of surface quality and review techniques for maintaining a high quality triangle mesh. Afterward, we will describe several methods for allowing the liquid surface to merge together or break apart. The final section of this course showcase the benefits and further applications of a meshbased liquid surface, highlighting stateoftheart methods for tracking colors and textures, maintaining liquid volume, preserving small surface features, and simulating realistic surface tension waves.
Hierarchical Distancebased Aggregation
, 2014
"... Approximation is one of the key techniques used in manipulating geometric objects. Aggregation is a form of approximation that joins objects that are likely to be grouped together as a single unit. This can improve efficiency, reduce complexity and generate levels of detail, and has application in ..."
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Approximation is one of the key techniques used in manipulating geometric objects. Aggregation is a form of approximation that joins objects that are likely to be grouped together as a single unit. This can improve efficiency, reduce complexity and generate levels of detail, and has application in rendering, cartography and molecular structure design. In this work, we present a general framework to aggregate nearby objects together. The proximity of the objects is determined based on distances between them. Grouped objects are approximated into shapes similar to alpha shapes. This reduces volume as compared to convex hull approximation. However, typical alpha shape approximation, which uses a constant alpha value, fails to adapt to nonuniform inputs. To address this, we use a function to adaptively determine the value of alpha based on the properties of the objects to be aggregated. Varying the threshold distance that determines the group of nearby objects, we can create a hierarchy of aggregation for any environment. We evaluate our method using two dimensional objects. The quality of the aggregated objects is evaluated using shape metrics including area, perimeter and circularity and is compared with convex hull and alpha shape approximations. Our method produces aggregates which are closer to the original objects than alpha shapes and convex hulls. We also demonstrate how the levels in aggregation can be used to solve motion planning problems more efficiently in complex environments. We have also extended our implementation to three dimensional objects with results similar to two dimensional environments. 1
The Visual Computer manuscript No. (will be inserted by the editor)
"... Abstract In this paper, we propose a hardware accelerated PDE (partial differential equation) solver based on the lattice Boltzmann model (LBM). The LBM is initially designed to solve fluid dynamics by constructing simplified microscopic kinetic models. As an explicit numerical scheme with only loca ..."
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Abstract In this paper, we propose a hardware accelerated PDE (partial differential equation) solver based on the lattice Boltzmann model (LBM). The LBM is initially designed to solve fluid dynamics by constructing simplified microscopic kinetic models. As an explicit numerical scheme with only local operations, it has the advantage of being easy to implement and especially suitable for graphics hardware (GPU) acceleration. Beyond the NavierStokes equation of fluid mechanics, a typical LBM can be modified to solve the parabolic diffusion equation, which is further used to solve the elliptic Laplace and Poisson equations with a diffusion process. These PDEs are widely used in modeling and manipulating images, surfaces and volumetric data sets. Therefore, the LBM scheme can be used as an GPUbased numerical solver to provide a fast and convenient alternative to traditional implicit iterative solvers. We apply this method to several examples in volume smoothing, surface fairing and image editing, achieving outstanding performance on contemporary graphics hardware. It has the great potential to be used as a general GPU computing framework for efficiently solving PDEs in image processing, computer graphics and visualization.