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We present experiments on latency and its compensation methods in a virtual reality application using a head-motion display (HMD) and a 3D-head tracker. Our purpose is to compare, both in simulation and in a real task, four tracker prediction methods: the grey system theory-based prediction, Kalman filtering, a simple linear extrapolation, and the basic method without prediction. Typical motion trajectories of the four methods in simulation are plotted, and jitter effects are examined. Kalman filtering was found to have the largest jitter among the four. An experiment is also presented to simulate a real-world application: following a tour guide in a walkthrough of a building. An improvement of 120% was observed.

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In this paper we propose a novel prediction method for the head motion using Grey System theory, where a 6D tracker is attached to an HMD on a user's head in virtual reality applications. Our prediction method using Grey System Model can greatly reduce the latency by at least one half and reduce image jittering. A system latency below 100 ms or even 50 ins can be achieved, even though without prediction the latency is around 200 ms. Using 6 points in prediction with Grey System Model is currently the best in tracker prediction as we tried from 2 points to 10 points. In order to measure the latency, we also propose a way to measure it in an HMD system precisely and conveniently. During the process, we have implemented four different prototypes respectively on a PC486, a SUN SparcStation10, an SGI IndigoR4000, and a high performance computer image generator. The computation complexity of our prediction method is relatively low and therefore real time requirement is easily met.

In this paper, we present the architecture of a new multimedia E-mail system, which has been successfully developed in the Communication and Multimedia Laboratory of National Taiwan University. This prototype E-mail system is fully compatible with traditional Internet E-mails in that the multimedia emails can be sent through Internet. For allowing one to compose multimedia emails, the system provides various editors for editing video, audio, image, graphics, and multilingual (English and Chinese) text. It is currently implemented on SUN Workstations with X-windows and OpenLook as its standard graphical user interface. In order to display video, the workstation are equipped with either an add-on video board or a software-based Codecs. Since its development, the system have been widely used in the National Taiwan University. Experience of users showed that the system is convenient to use and is indeed fully compatible with the traditional Internet E-mails.