Professional 3D digital content creation tools, like Alias Maya or discreet 3ds max, offer only limited support for a team of artists to work on a 3D model collaboratively. We present a scene graph repository system that enables fine-grained collaboration on scenes built using standard 3D DCC tools by applying the concept of collaborative versions to a general attributed scene graph. Artists can work on the same scene in parallel without locking out each other. The artists’ changes to a scene are regularly merged to ensure that all artists can see each others progress and collaborate on current data. We introduce the concept of indirect changes and indirect conflicts to systematically inspect the effects that collaborative changes have on a scene. Inspecting indirect conflicts helps maintaining scene consistency by systematically looking for inconsistencies at the right

Professional 3D digital content creation tools, like Alias Maya or discreet 3ds max, offer only limited support for a team of artists to work on a 3D model collaboratively. We present a scene graph repository system that enables fine-grained collaboration on scenes built using standard 3D DCC tools by applying the concept of collaborative versions to a general attributed scene graph. Artists can work on the same scene in parallel without locking out each other. The artists' changes to a scene are regularly merged to ensure that all artists can see each others progress and collaborate on current data. We introduce the concept of indirect changes and indirect conflicts to systematically inspect the effects that collaborative changes have on a scene. Inspecting indirect conflicts helps maintaining scene consistency by systematically looking for inconsistencies at the right places.

In recent years, interactive ray tracing has become a reality, although mainly by using clustered workstations and sophisticated acceleration structures. On non-clustered computer architectures this is still not an easy task, especially when rendering animated scenes, even though the computation power of modern workstations is increasing rapidly. In this paper we propose known image-space rendering techniques to be used for accelerating ray tracing. Firstly, we describe a GPU-based visibility preprocessing algorithm to perform interactive ray casting by applying the standard depth testing capability of graphics processing units. This method - called object intersection buffer (OIB) - is particularly suitable for ray casting animated scenes, as it completely avoids the necessity of creating and updating any kind of spatial acceleration structures in order to achieve high frame rates. Then we integrate shadow rendering into our ray caster using the shadow mapping technique to avoid computationally expensive shadow rays. Then, we convert our GPU-based ray caster into a hybrid ray tracer by computing reflection and refraction rays on the CPU using a spatial acceleration structure. This allows us to exploit parallel rendering to increase the overall frame rate. Finally, we compare our implementations to each other and analyse their advantages and disadvantages in terms of visual quality and rendering performance.

Background: The Pulfrich stereoillusion occurs spontaneously in diseases inducing asymmetric visual pathway delays. Its influence on driving performance has never been investigated and was, therefore, assessed using a three-dimensional (3D) computer driving simulation. Methods: A 3D driving scenery of a road with obstacles was visualised on an autostereoscopic 3D display. Seven normal subjects drove at a speed of 6 m/s using a steering wheel and three angles of view of the scenery (0 degrees, 45 degrees to left, and 90 degrees to left) with different interocular delays (25 ms on the right, 25 ms on the left, and no delay). One subject drove the scenery at an angle of 90 degrees without delay and with a delay of 8 ms, 16 ms, and 25 ms on the right and left, respectively, at speeds of 6 m/s,12 m/s and 18 m/s. Results: Stereoillusion only influenced car position if the angle of view was 90 degrees (p < 0.05). At this angle, increasing car speeds were associated with larger car displacements (delay on right p < 0.001, on left p < 0.01) and smaller delays with smaller car displacements (p < 0.001). Conclusions: This study showed that Pulfrich phenomenon has an influence on car position only if the viewing angle is 90 degrees. No influence could be found if the driving direction corresponded to the visual axis of the driver. These findings are in agreement with reports of patients with spontaneous Pulfrich phenomenon who indicate that while driving, distances are only misjudged when looking sideways.

Geometric Modeling is that field within Computer Science which is concerned with the efficient processing of geometric information on a computer. It combines techniques from Computer Science, Mathematics and Engineering and attracts researchers with different scientific backround. Application areas of Geometric Modeling include CAD/CAM, Computer Graphics, Medical Imaging and Scientific Visualization. The fourth Dagstuhl seminar on Geometric Modeling was attended by 56 participants from 15 different countries. Among these the leading experts of the field were present as well as a several young researchers who received financial support from the European TMR-programm. For the second time during a Dagstuhl seminar the John A. Gregory Memorial Award was awarded to the pioneers of the field of Geometric Modeling. The talks presented at the conference concerned the problem areas of

An algorithm Sweepplane is presented to be used as an auxiliary algorithm by space-sweep algorithms requiring a sweep plane in regular position, i.e., a sweep plane which never meets ≥2 event points at the same time. Sweepplane is an on-line algorithm which ensures that the regular position of the sweep plane is never destroyed by a new event point created during the sweep. If necessary, it dynamically replaces the actual sweep plane by a more suitable one, but always in such a way that the induced order of the event points already swept is maintained.

Medieval Burgundian tapestries belong to the most valuable treasures of historical museums, in particular of the Bern Historical Museum. Many of them are well preserved, but much of their color is highly faded. Thus their today's appearance is very different from the original one. This paper deals with the digital restoration of the appearance of such tapestries. Two methods are developed and examined, one using the back side of the tapestry, the other one using color clustering. Our main criteria are a convincing approximation of the expected appearance and - due to the large size of many of the tapestries - a high degree of automation.

We present algorithms for the efficient insertion and removal of constraints in Delaunay Triangulations. Constraints are considered to be points or any kind of polygonal lines. Degenerations such as edge overlapping, self-intersections or duplicated points are allowed and are automatically detected and fixed on line. As a result, a fully Dynamic Constrained Delaunay Triangulation is achieved, able to efficiently maintain a consistent triangulated representation of dynamic polygonal domains. Several applications in the fields of data visualization, reconstruction, geographic information systems and collision-free path planning are discussed.

M2S 1 is a Java application for creating virtual worlds based on road maps. A user scans an ordinary road map with a color scanner. M2S analyzes the image and produces a virtual world which is in accordance with the map. A rich user-interface lets the user edit and complete the generated 3D-model. A large number of properties can be set: from the background-image via the level of detail up to the algorithm to be used for a specific task. An included fly-through serves to explore and evaluate the result. The exporter tool of M2S currently supports VRML97 and Microsoft's X file format.

This paper presents a new architecture of a database system for the management of graphics objects. The motivation for designing this architecture is to improve the reuse of graphics objects and graphics functionality. This shall be achieved by a component-based approach that offers database facilities to existing graphics applications and allows graphics functionality of different origins to be integrated. The system shall also be easily accessible to remote users. Such a system has to cope with the large variety of data representations typically found in the graphics domain. The idea of the present approach is to store the data in its original form, without prior conversions, thus conserving the maximum information content. A special type model, separating semantics from implementation, ensures type safeness and, at the same time, provides the flexibility and extensibility needed to cope with multiple data representations. Software components enable seamless integration of the existing graphics operations offered by various software packages. The components, together with a composition mechanism, act as the data manipulation language of the architecture. The architecture to be presented has been implemented in a prototype system called GSCOPE, which is accessible via the Internet.

A Nef polyhedron is any set in ℝd which can be obtained by applying a finite number of Boolean set operations cpl and ∩ to finitely many (open) linear halfspaces. After resuming some fundamentals, it is shown in which sense several kinds of well-known polyhedra are special cases of Nef polyhedra. Then a number of representations of Nef polyhedra are presented and discussed, and algorithms for converting them into each other are given.

A Nef polyhedron is any set in ℝ d (d∈ ℕ0) which can be obtained by applying a finite number of Boolean set operations cpl and ∩ to (open) linear halfspaces. This paper summarizes the fundamentals of the theory of Nef polyhedra and illustrates them by means of simple 2D examples. The notions of Nef polyhedron, locally adjoined pyramid and face of a Nef polyhedron are carefully explained. Data structures for representing Nef polyhedra are discussed, and an implemented test-system is presented with the aid of a small application.