29746533
Guidance of Users in Interactive 3D-Visualisations of Material Flow Simulations
15975823
The randomized z-buffer algorithm: interactive rendering of highly complex scenes
We present a new output-sensitive rendering algorithm, the randomized z-buffer algorithm. It renders an image of an arbitrary three-dimensional scene consisting of triangular primitives by reconstruction from a dynamically chosen set of random surface sample points. This approach is independent of mesh connectivity and topology. The resulting rendering time grows only logarithmically with the numbers of triangles in the scene. We were able to render walkthroughs of scenes of up to 1014 triangles at interactive frame rates. Automatic identification of low detail scene components ensures that the rendering speed of the randomized z-buffer cannot drop below that of conventional z-buffer rendering. Experimental and analytical evidence is given that the image quality is comparable to that of common approaches like z-buffer rendering. The precomputed data structures employed by the randomized z-buffer allow for interactive dynamic updates of the scene. Their memory requirements grow only linearly with the number of triangles and allow for a scene graph based instantiation scheme to further reduce memory consumption.
14681345
The randomized sample tree: a data structure for interactive walkthroughs in externally stored virtual environments
We present a new data structure for rendering highly complex virtual environments of arbitrary topology. The special feature of our approach is that it allows an interactive navigation in very large scenes (30 GB/400 million polygons in our benchmark scenes) that cannot be stored in main memory, but only on a local or remote hard disk. Furthermore, it allows interactive rendering of substantially more complex scenes by instantiating objects.For the computation of an approximate image of the scene, a sampling technique is used. In the preprocessing, a so-called sample tree is built whose nodes contain randomly selected polygons from the scene. This tree only uses space that is linear in the number of polygons. In order to produce an image of the scene, the tree is traversed and polygons stored in the visited nodes are rendered. During the interactive walkthrough, parts of the sample tree are loaded from local or remote hard disk.We implemented our algorithm in a prototypical walkthrough system. Analysis and experiments show that the quality of our images is comparable to images computed by the conventional z-buffer algorithm regardless of the scene topology.
7434194
Multi-user support and motion planning of humans and humans driven vehicles in interactive 3D material flow simulations
The visualization of simulated production processes is used for their analysis. Huge plants are normally planned by a team. So a solution for many users who are modeling and interacting with a running model in an immersive 3D environment is required. We discuss an approach where several users work cooperatively on one simulation model. To optimize their work, the users need some guidance. For this we suggest small maps and arrows to guide the user to significant objects (machines). In many production scenarios, objects (forklifts, workers) are moving in an unguided fashion. In actual implementations these paths have to be modeled manually. In spite of taking these efforts, we are presenting an automated approach which is based on the 3D layout of the plant. If the user as part of the simulation is standing in the way of the object, the object stops in our approach (as hopefully in reality).
9204420
Partitioned neighborhood spanners of minimal outdegree
A geometric spanner with vertex set P IRD is a sparse approximation of the complete Euclidean graph determined by P. We introduce the notion of partitioned neighborhood graphs (PNGs), unifying and generalizing most constructions of spanners treated in literature. Two important parameters characterizing their properties are the outdegree k IN and the stretch factor f 1 describing the ‘quality’ of approximation. PNGs have been thuroughly investigated with respect to small values of f . We, on the other hand, present in this work results about feasable values of k — so to say the other extreme. The aim of minimizing this parameter rather than the first one arises from two observations: a) It determines the amount of space required for storing PNGs. b) Many algorithms employing a (previously constructed) spanner have running times depending on its outdegree. Our results include, for fixed dimensions D as well as asymptotically, upper and lower bounds on this optimal value of k. The upper bounds are constructive and yield efficient algorithms for actually computing the corresponding graphs. 1Partially supported by EU ESPRIT Long Term Research Project 20244 (ALCOM-IT) and DFG Grants Me872/7-1 and Me872/4-1
16340460
Bi-directional Coupling of Simulation Tools with a Walkthrough-System
Visualising is amethod used to help experiencing a nd understanding causal cohesions in simulation processes. For this purpose, tools for visualising are already implemented in prevalent simulation systems. The user creates his imulation model and generates a 3-dimensional (2,5-dimensional) visualising by means of the simulation system. This helps examining the process which makes it easier for the viewer to “understand” it. Simulatio n tools usually only provide the opportunity for a unidirectional visualising. In a 3-dimensional surr ounding the viewer can not implement an interaction with the simulation while the system is running. Though an interaction during the simulation run enables the user to gain a better un derstanding of causal cohesions. Solutions via HLA are sophisticated and therefore rather suited f or extensive projects. We present a distributed system consisting of a com mercial manufacturing simulation tool, a coupling module and a walkthrough system. The distr ibuted system in conjunctions with the coupling module guarantees generality and a wide field of applications of the walkthrough system. Further it guarantees flexibility and selection of the specialized graphics hardware for the walkthrough system. A further contribution of this paper is the solution of the time synchronisation problem caused by simulation tool and walkthrough s ystem.
17113954
INTEGRATING ANTHROPOLOGICAL APPROACHES TO THE STUDY OF CULTURE: THE “HARD” AND THE “SOFT”
Much anthropological interest in methods derived from the natural sciences has been motivated by a search for tools with which to describe ethnographic settings in more “rigorous” terms. These have generally failed, and these failures are due to implicit conventions in anthropology regarding what to observe and how. I suggest that natural science methods were developed as a result of a process that aimed to solve problems that are generally different from those that social scientists pursue and that social scientists need to take the underlying ideas and rebuild them for their own purposes if they want to import them. Likewise, most qualitative anthropologists are also guilty of inappropriate borrowing, in particular in their importation of postmodern philosophy from literary criticism rather than adapting these ideas from the source in a manner more suited to the discipline. I examine some the conditions that would be necessary to integrate the various fractions of the anthropological community within a flexible but common framework. I conclude that anthropology must include a major qualitative perspective and, in response to this, suggest that if we are to formalize our study we must adopt some new conventions. These include a broadening of analysis beyond causality to include interpretive reasoning within a common framework, the addition of deontic operators to our basic formal framework, and an emphasis on declarative semantics over procedural semantics. We end by briefly describing some speculative work using Information Theory as a basis for quantitatively evaluating qualitative descriptions, models, and analysis.
15236721
Bounds on secret key exchange using a random deal of cards
We present a general model for communication among a “team” of players overheard by a passive eavesdropper, Eve, in which all players including Eve are given private inputs that may be correlated. We define and explore secret key exchange in this model. Our secrecy requirements are information-theoretic and hold even if Eve is computationally unlimited. In particular, we consider the situation in which the team players are dealt hands of cards of prespecified sizes from a known deck of distinct cards. We explore when the team players can use the information contained in their hands to determine a value that each team player knows exactly but Eve cannot guess.
62681368
Lambda-calculus schemata
A lambda-calculus schema is an expression of the lambda calculus augmented by uninterpreted constant and operator symbols. It is an abstraction of programming languages such as LISP which permit functions to be passed to and returned from other functions. When given an interpretation for its constant and operator symbols, certain schemata, calledlambda abstractions, naturally define partial functions over the domain of interpretation. Two implementation strategies are considered: the retention strategy in which all variable bindings are retained until no longer needed (implying the use of some sort of garbage-collected store) and the deletion strategy, modeled after the usual stack implementation of ALGOL 60, in which variable bindings are destroyed when control leaves the procedure (or block) in which they were created. Not all lambda abstractions evaluate correctly under the deletion strategy. Nevertheless, both strategies are equally powerful in the sense that any lambda abstraction can be mechanically translated into another that evaluates correctly under the deletion strategy and defines the same partial function over the domain of interpretation as the original. Proof is by translation into continuation-passing style.
6874024
Optimal Layout of Edge-weighted Forests
The layout problem for trees with weighted edges is motivated by the design of very-large-scale integrated circuits. Some of the nodes are fixed and the object is to position the remainder so that the total weighted edge cost is minimized. The cost of each edge is the product of its weight and its length under some appropriate norm. Optimization for planar layouts is shown to be NP-hard. If crossings are permitted, then optimal layouts under the L1 norm can be efficiently computed. Suitable algorithms and data structures are presented, and explicit exact cost functions are given for two classes of weighted complete binary trees.
1648746
Experience in early and late software engineering project courses
We report on the experience we gained in different software engineering project courses at our department. A student who is specialized in software engineering has to complete, besides lectures on software engineering and related fields, two project courses: an "early" basic project course, and a "late" complex project course. For both of them we developed leveled teaching approaches considering the different knowledge and skills of beginners and "advanced" students, respectively. The paper describes, discusses and evaluates these approaches.