Nils Jensen

An efficient system for collaboration in tele-immersive environments

The paper describes the development of a high-performance system for visualizing complex scientific models in real-time. The architecure of the system is a client/server model, in which the simulator generates lists of 3D graphics objects in parallel to the simulation, from where they are sent to a streaming server. The server transfers the 3D objects to viewer clients. Clients communicate over a second connection with each other, which adds the ability to perform collaborative tasks. An application related to computational fluid dynamics is specified where such a tele-immersive system can be used. The approach differs to other solutions because it offers a large set of graphics primitives for visualization, and it is optimized for distributed, heterogenous environments.

Covase: Collaborative Visualization for Constructivist Learning

The paper specifies CoVASE, a software for teachers to create and view networked learning environments (VE). Students carry out virtual experiments in CoVASE, at the same time and different places. ...

Design and Psychophysical Study of Volume Compression for Haptic Rendering

The paper specifies a novel coder/decoder that compresses sequences of 3D texture data to support the haptic rendering of animated volumes. Lossy compression gives 25% of the original size. Lossy compression and clipping gives 3% but requires the renderer to query for new data when the point of contact moves. We evaluated the codec by means of rendering volumes on a 3-DOF Phantom 1.5A that simulated viscosity for each texture element. In this setting, we studied the impact of information loss in controlled experiments. We validated that our codec preserves haptic perception. An area of application is the development of network-distributed virtual environments that generate visual and haptic feedback

Efficient 1-pass prediction for volume compression

The aim is to compress and decompress structured volume graphics in a lossless way. Lossless compression is necessary when the original scans must be preserved. Algorithms must deliver a fair compression ratio, have low run-time and space complexity, and work numerically robust. We have developed PR0 to meet the goals. PR0 traces runs of voxels in 3D and compensates for noise in the least significant bits by way of using differential pulse-code modulation (DPCM). PR0 reduces data to 46% of the original size at best, and 54% on average. A combination of PR0 and Worst-Zip (Zip with weakest compression enabled) gives reductions of 34% at best, and 45% on average. The combination takes the same or less time than Best-Zip, and gives 13%, respectively 5%, better results. To conduct the tests, we have written a non-optimised, sequential prototype of PR0, processed CT and MRI scans of different size and content, and measured speed and compression ratio.

Using Conceptual Structures in the Design of Computer-Based Assessment Software

This paper discusses the use of conceptual structures in the design of computer-based assessment (CBA) tools for e-assessment of programming exercises. In STEM (science, technology, engineering and maths) subjects, universities often observe high dropout and failure rates among the first year students. There are a number of research initiatives that investigate the use of interactive teaching methods and e-learning technologies for improving STEM education. This paper presents a conceptual model of programming exercises and discusses more generally how conceptual structures can be employed for the implementation of CBA tools.