Thomas C. Hudson

VRPN: a device-independent, network-transparent VR peripheral system

The Virtual-Reality Peripheral Network (VRPN) system provides a device-independent and network-transparent interface to virtual-reality peripherals. VRPNs application of factoring by function and of layering in the context of devices produces an interface that is novel and powerful. VRPN also integrates a wide range of known advanced techniques into a publicly-available system. These techniques benefit both direct VRPN users and those who implement other applications that make use of VR peripherals.

Visibility culling using hierarchical occlusion maps

We present hierarchical occlusion maps (HOM) for visibility culling on complex models with high depth complexity. The culling algorithm uses an object space bounding volume hierarchy and a hierarchy of image space occlusion maps. Occlusion maps represent the aggregate of projections of the occluders onto the image plane. For each frame, the algorithm selects a small set of objects from the modelas occludersand renders them to form an initial occlusion map, from which a hierarchy of occlusion maps is built. The occlusion maps are used to cull away a portion of the model not visible from the current viewpoint. The algorithm is applicable to all models and makes no assumptions about the size, shape, or type of occluders. It supports approximate culling in which small holes in or among occluders can be ignored. The algorithm has been implemented on current graphics systems and has been applied to large models composed of hundreds of thousands of polygons. In practice, it achieves significant speedup in interactive walkthroughs of models with high depth complexity. CR

V-COLLIDE: accelerated collision detection for VRML

Collision detection is essential for many applications involving simulation, behavior and animation. However, it has been regarded as a computationallydemanding task and is often treated as an advanced feature. Most commonly used commercial CAD/CAM packages and high performance graphics libraries, such as SGI Performer, provide limited support for collision detection. As users continue to stretch the capabilities of VRML, collision detection will soon become an indispensable capability for many applications. In this paper, we present a system for accelerated and robust collision detection and describe its interface to VRML browsers. We demonstrate that it is possible to perform accurate collision detection at interactive rates in VRML environments composed of large numbers of complex moving objects. CR

MMR: an interactive massive model rendering system using geometric and image-based acceleration

We present a system for rendering very complex 3D models at interactive rates. We select a subset of the model as preferred viewpoints and partition the space into virtual cells. Each cell contains near geometry, rendered using levels of detail and visibility culling, and far geometry, rendered as a textured depth mesh. Our system automatically balances the screen-space errors resulting from geometric simplification with those from textureddepth-mesh distortion. We describe our prefetching and data management schemes, both crucial for models significantly larger than available system memory. We have successfully used our system to accelerate walkthroughs of a 13 million triangle model of a large coal-fired power plant and of a 1.7 million triangle architectural model. We demonstrate the walkthrough of a 1.3 GB power plant model with a 140 MB cache footprint.

In situ resistance measurements of strained carbon nanotubes

We investigate the response of multiwalled carbon nanotubes to mechanical strain applied with an atomic force microscope probe. We find in some samples, changes in the contact resistance dominate the measured resistance change. In others, strain large enough to fracture the tube can be applied without a significant change in the contact resistance. In this case, we observe that enough force is applied to break the tube without any change in resistance until the tube fails. We have also manipulated the ends of the broken tube back in contact with each other, re-establishing a finite resistance. We observe that, in this broken configuration, the resistance of the sample is tunable to values 15–350 kΩ greater than prior to breaking.

Beyond audio and video: multimedia networking support for distributed, immersive virtual environments

Like interactive audio/video applications, distributed virtual environments (DVEs) require continuous, low-latency delivery of media. While end-system media adaptations and network-based forwarding services have been developed to support audio/video applications, it remains an open question whether these mechanisms can be either directly applied or adapted to realize the requirements of DVEs. We present the results of a study on the use of audio/video media adaptations and router-based active queue managements (AQM) to support the data-flows generated by the UNC nanoManipulator-a DVE interface to a scanned-probe microscope. We present a delay-jitter management scheme used to support a haptic force-feedback tracking/pointing device used in the nanoManipulator and an AQM scheme based on buffer allocation in routers to reduce packet loss. The results of early experiments are promising and provide evidence that a sophisticated virtual environment interface can operate over the Internet to control a remote microscope in real-time.

Experiments in best-effort multimedia networking for a distributed virtual environment

Until there is greater consensus on proposals for realizing better-than-best-effort services on the Internet, developers of multimedia and distributed virtual environment applications must rely on best-effort media adaptations to ameliorate the effects of network congestion. We present the results of a study on the use of adaptations originally developed for audio and video applications for the data-flows generated by the UNC nanoManipulator. The nanoManipulator is a virtual environment interface to a scanned-probe microscope that has been used by scientists as a tool for basic research in the material and biological sciences. We are building a distributed version of the system for operation over the Internet and are investigating media adaptations for realizing application performance requirements. The results of early experiments with audio and video-centric media adaptations applied to the flows generated by a microscope and a haptic force feedback device are promising. A simple forward error correction scheme provides good recovery from packet loss and an elastic display-queue management scheme limits the impact of delay- jitter and results in more continuous playout of media samples. These preliminary results provide evidence that a sophisticated virtual environment interface can operate over modest distances over the Internet to control a remote microscope in real-time.

Managing collaboration in the nanoManipulator

We designed, developed, deployed, and evaluated the Collaborative nanoManipulator (CnM), a system supporting remote collaboration between users of the nanoManipulator interface to atomic force microscopes. To be accepted by users, the shared nanoManipulator application had to have the same high level of interactivity as the single user system and the application had to support a users ability to interleave working privately and working collaboratively. The paper describes the entire collaboration system, but focuses on the shared nanoManipulator application. Based on our experience developing the CnM, we present: a method of analyzing applications to characterize the requirements for sharing data between collaborating sites, examples of data structures that support collaboration, and guidelines for selecting appropriate synchronization and concurrency control schemes.

Enabling distributed collaborative science

CSCW’00, December 2-6, 2000, Philadelphia, PA. ACM 1-58113-222-0/00/0012. Enabling Distributed Collaborative Science Tom Hudson1, Diane Sonnenwald2, Kelly Maglaughlin2, Mary Whitton1, and Ronald Bergquist2 1Department of Computer Science 2School of Information and Library Science University of North Carolina, Chapel Hill University of North Carolina, Chapel Hill Campus Box 3175, Sitterson Hall Campus Box 3360, Manning Hall Chapel Hill, NC 27599-3175 Chapel Hill, NC 27599-3360 {hudson, whitton}@cs.unc.edu {dhs, maglk, bergr}@ils.unc.edu

Minimal marker sets to discriminate among seedlines

Raising seeds for biological experiments is prone to error; a careful experimenter will test in the lab to verify that plants are of the intended strain. Choosing a minimal set of tests that will discriminate between all known seedlines is an instance of Minimal Test Set, a NP-complete problem. Similar biological problems, such as minimizing the number of haplotype tag SNPs, require complex nondeterministic heuristics to solve in reasonable timeframes over modest datasets. However, selecting the minimal marker set to discriminate among seedlines is less complicated than other problems considered in the literature; we show that a simple heuristic approach works well in practice. Finding all minimal sets of tests to identify 91 Zea mays recombinant inbred lines would require months of CPU time; our heuristic gives a result less than twice the minimal possible size in under five seconds, with similar performance on Arabidopsis thaliana recombinant inbred lines.