Fully Wireless, Full Body 3-D Motion Capture for Improvisational Performances V. Lympourides Department of Music University of Edinburgh Edinburgh EH8 9DF, UK vl_artcode@yahoo.com D. K. Arvind Research Consortium in Speckled Computing School of Informatics University of Edinburgh Edinburgh EH8 9AB, UK dka@inf.ed.ac.uk Martin Parker Department of Music University of Edinburgh Edinburgh EH8 9DF, UK martin.parker@ed.ac.uk ABSTRACT This paper describes a framework for exploring the boundaries of interactive whole-body improvisational performances using the Orient-3 Wireless Motion Capture System in collaboration with composers and musicians. The requirements for improvisational performances are explored and the choice of the Orient-3 motion capture system is justified from among mechanical, acoustic, magnetic, optical and inertial motion capture methods. Categories and Subject Descriptors C.2 [Computer-Communication Networks]: Network Architecture and Design – Wireless Communication. H.5 [Information Interfaces and Presentation]: Multimedia Information Systems – Animations; User Interfaces – Input Devices. J.5 [Computer Applications]: Arts and Humanities – Performing arts (Dance and Music). General Terms Design, Experimentation, Human Factors, Measurement, Performance. Keywords Wireless Motion Capture, Full-body Motion Capture. 1. INTRODUCTION Motion capture is the recording of motion for either real-time or delayed analysis, and playback. Subsequent analysis of the data is used in a wide range of applications including clinical studies, i.e., gait analysis, sports science, i.e., biomechanical studies in skill acquisition, and computer animation. A number of classical motion capture methods ranging from mechanical, acoustic, magnetic, optical and intertial methods are described in Section 2. A full body, fully wireless, 3-D motion capture system is described in Section 3 and its choice for interactive improvisational performances is justified in Section 4, with early results and plans for future research described in the rest of the paper. 2. MOTION CAPTURE METHODS Classical motion capture techniques [2] are distinguished by the location of the sensors - either external to, or on the subject, and the nature of the transducers employed – mechanical, acoustic, magnetic, optical or inertial. Prosthetic or mechanical motion capture methods require the subject to wear an external structure or exoskeleton, and the posture is determined by detecting changes in the optical or electrical transducers at the joints. The main disadvantage is the cumbersome external structure, whereas the many advantages are the direct computation of rotation, simultaneous capture of multiple subjects without problems of occlusion, portability and relatively low cost. In the acoustic motion capture method, audio transmitters are attached to the performer and the external receivers measure the time to receive the signal, and compute the position of the transmitters using triangulation. As in the previous method, the principal advantage is the lack of occlusion in the case of multiple performers, whereas the many disadvantages include unwieldy wires, limited size of the capture area, reflections of sound compromise accuracy, and the low rate of transmission only supports limited number of transmitters. Magnetic motion capture method uses a large central magnetic transmitter to compute the position and orientation of the receivers attached to the person. The lack of occlusion is the principal advantage; disadvantages include the cabling which inhibits movements, interference from metal in the vicinity, and the limited capture volume. Optical motion capture (Vicon [3], Qualisys [4], Motion Capture [5]) is probably the most widely used method in which either passive reflective markers or active markers are attached to a performer, and a system of fixed cameras record the position of these markers. This approach allows the performer greater freedom of movement, and achieves faster sampling at a high resolution than the previous methods, in a capture area which is normally larger in comparison to the acoustic and magnetic methods. This method is by far the most expensive and suffers from problems of occlusion. Extensive post processing is required in order to locate and identify the markers and account for any crossovers. A typical optical motion capture session is both a time- consuming and expensive process with well-defined phases: planning, setting-up and calibration, capturing of performance, post-processing for the identification and location of markers, © The Author 2007. Published by the British Computer Society