This article describes the development of LiteFoot, an interactive floor space that tracks dancer's steps, converting human motion into auditory and visual display. The system can also record steps for further analysis for use in dance research programmes, choreographic experimentation and training.

Introduction
In early 1997 a team of researchers at the University of Limerick started to discuss the prospects of recording traditional Irish dance electronically and also how an electronic recording device could potentially be made to add to, or enhance, performance through sound and visual representations of dance. If such a system could be created, it would potentially allow researchers in ethnochoreology to record and analyse the subtle movements of master dancers as well as allowing modern dancers to explore possibilities with a dancer making his or her own music in real-time.

We were inspired by performers like Laurie Anderson who already in 1983 'butchered' a drum-machine and stitched the sensor pads into a jacket. The output from the drum-machine was normally digitised sounds of drums, but Laurie had the sounds changed into heartbeats, breath, etc. Drum-machines also have MIDI interfaces which implies that the output can also be used for controlling other synthesizers. Other sources of inspiration were systems like Ascension Technology Corporation's MotionStar Wireless which is a set of up to 20 position sensors fitted on a performer. Data from the sensors can be transmitted through high-speed telemetry, recorded and converted into coordinates. The main drawback with MotionStar is that it is quite expensive. It is also slightly invasive as the dancer's body has to be fitted with sensors and a back-pack with radio and batteries for the telemetry. A number of dance oriented systems exists, such as the PodoBoard which was developed to facilitate a form of seated dance known as clackage that normally takes place on a small wooden floor. The PodoBoard provides an accurate set of co-ordinates for the position of feet contact with the floor, which is a matrix of 25 millimetres square aluminium tiles. The floor's reaction to footsteps is extremely fast but the dancer has to wear shoes with metal contacts. The system relies on good electrical connection between shoe and floor. A different solution was developed by Pinkston, with force sensors arranged in strips. The resolution of the system is approximately 152 millimetres. Although it is a useful floor, the sensor technology is relatively expensive. The system is designed to detect the events of footsteps, not the precise co-ordinates. It might be possible, by using orthogonal, overlapping strips to calculate positions, but as the floor size increases it is likely to be impractical.

Figure 1: Sensor principle

Another possible solution is Paradiso's Magic Carpet which is using a technology based on a
mat inlaid with cables that are insulated with a material that responds to compression and
bending by producing a change in capacitance. The cables are multiplexed and scanned 60 times
per second. The floor is very sensitive to foot pressure. It was designed to allow people in
public spaces to create and manipulate a sound environment. There are a number of aspects that
again make it less useful as a medium for recording, dance. Firstly, the resolution of the floor is
100 millimetres which is a relatively coarse resolution when considering the translation of steps
into a choreographic representation. The rate of detection also has difficulties to cope with for example Irish traditional dance where steps can be as rapid as 30 per second. The system scans the periphery of the total area hence the Magic Carpet has difficulties locating the steps of more than one foot at once, i.e. that one foot can 'shadow' another. All these designs have in common that their output can be recorded and/or control a MIDI synthesizer. Having, reviewed the existing systems we found that existing systems were either expensive, invasive or not fulfilling, the requirements.

Designing LiteFoot
A number of issues had to be covered, both users' requirements and technical requirements versus constraints such as budget and a definite deadline - UL's 25th anniversary (in 1997). The following requirements were identified as key elements for this design:

· The floor should be able to respond at a rate corresponding, to at least 30 steps per second.
· The floor should have a reasonable spatial resolution (44 millimetres)
· The floor should be able to track multiple feet and dancers.

Figure 2: System Architecture

The LiteFoot prototype is a 1.76 meter square and 10 centimetres high floor element, filled with a matrix of 1,936 optical proximity sensors. Each sensor has an infra-red light-emitting diode and a phototransistor. When an object comes close to the sensor, approximately 6 millimetres, the light from the diode is reflected back and 'seen' by the transistor. When you stand on the floor the spatial locations of your feet are detected. An accelerometer detects the total impact force of the feet, providing a third dimension. The floor has an embedded micro-controller that scans all sensors 100 times per second. If any change occurred since last scan, a message is sent via a serial high-speed connection to a PC running two special application programs, 'TipTapToe' and 'FootWare'. The former handles the serial communications and the latter interprets the received data and converts it into computer controlled sounds and graphics. The fundamental principles underlying the LiteFoot software are that the software enables simultaneous modes of independent use, i.e. performance and recording to take place concurrently. Arbitrary mappings between the data coming from the floor and representations can be defined by the user. The visual representation has, so far, been a direct mapping of location to displayed groups of pixels, with the colour controlled by the impact force. For the auditory representation, the incoming data-stream controls the MIDI synthesizer of a standard sound card, with various musical scales in one dimension (X) and various sets of 'instruments' in another dimension (Y). The impact force has been mapped to, for example, loudness (Z).

LiteFoot in Action
The LiteFoot premiere was in September 1997 in a performance in the University Concert Hall at LTL. Both traditional Irish dance an improvised modern dance was performed and several members of the audience reported the performance to be aesthetically and perceptually engaging. In January 1998 LiteFoot appeared in 'The Late Late Show' as an example of new art and technology. We had to rewrite some of the software, as the lighting, in RTE's television studio was so bright that we could not use the reflected infra-red light from the built-in light-emitting diodes. The modified version of the software was instead 'looking,' at the shadow of the dancer in this particular performance.
Since then it has been demonstrated several times, including an international workshop on dance at the University of Limerick (Trath na gCos) and in an interactive exhibition in Limerick City (Infusion - a National Review of Live Art). We have also tried to use LiteFoot as a sound sculpture, in a submission to the Prix Ars Electronica 98 in Austria. Sheets of tinfoil were suspended from the ceiling, brushing against the LiteFoot floor. The slightest breeze (for example from a person passing) would make the tinfoil move, resulting in sounds and graphics. The graphics were projected on the tinfoil.

Figure 3: Mapping performance to sound and graphics

From the comments from users, the following future applications have been suggested:

· Training, - a dance teacher can not only tell a student to 'do as you see me doing' but also, at the same time, 'do as you hear me doing'. Training modes could be both direct or differential (to make differences between teacher and student visible and audible).

· Performance - Enabling persons to have the motion of their feet converted into musical structures opens up a number of new possibilities in performing arts. A dancer can produce his or her own accompaniment, and the system can make very small and subtle movements visible and audible.

· Play - In the Infusion exhibition mentioned above, the LiteFoot system was exhibited as an interactive installation. It was much appreciated by children who could just by walking, jumping and crawling. on it, produce sounds and visuals controlled by their actions.

Continued Research
With the existing, LiteFoot prototype, we can now evaluate its use to define the requirements for a second Generation of LiteFoot. Several final year projects in the Department of Computer Science and Information Systems at UL have extended our software libraries. We are currently recruiting two Ph.D. students to work on enhanced sensors, integration and processing of the different data streams. There are many possibilities to be explored, for example, to use other kinds of mappings. Instead of direct mappings, orchestrations and sound, music or video sequences with parametric control could be mapped to areas of the floor. When several persons are active on the floor simultaneously, the level of 'collaborative harmony' could be mapped to tonal harmony and temporal structures. From the input data, higher order products could be integrated or derived, to allow for example the acceleration of a movement to be mapped to properties of sounds and graphics. As a play space, LiteFoot seems to be highly engaging and there are also a number of possibilities to be evaluated with for example disabled people who might be able to extend their action range through training with different forms of auditory and visual feedback.

Figure 4: Possible future architecture based on student's Final Year Projects

Acknowledgements
The LiteFoot team is an expanding interdisciplinary group and it is almost impossible to list all contributors to this project. The core of the group, so far, is Dr. Niall Griffith (CSIS), Dr. Liam Bannon (IDC/CSIS) and Dr. Catherine Foley (IWMC). I also would like to thank Prof. Kevin Ryan for his financial support and the Department of CSIS for financial support and the loan of equipment during, the development.

Bibliography
E. Johnstone, "A MIDI foot controller - The PodoBoard," Proceedings of International Computer Music Conference, San Francisco, 199 1.

H. Leopoldseder, C. Schöpf (Editors), "Cyberarts 98 - International Compendium Prix Ars
Electronica", Springer-Verlag, Wien New York, 1998.

R. Pinkston, J. Kerkhoff, and M. McQuilken, "A Touch sensitive Dance Floor/MIDI Controller,"
Proceedings of International Computer Music Conference, San Francisco, 1995.

J. Paradiso, C. Abler, K. Hsiao, and M. Reynolds, "The Magic Carpet: Physical Sensing for Immersive Environments," Proceedings of CHI'97, Atlanta, GA, USA, 1997.

HOMEpage OF THE BRAVE: Laurie Anderson, http://www.cc.gatech.edu/~jimmyd/laurie-anderson/
LiteFoot Homepage, http://www.ul.ie/~pal/litefoot/

Biography
Mikael Fernström works as Research Officer in the Interaction Design Centre at UL and also as a lecturer in the CSIS department. In addition, he is also working on his Ph.D. - Ecological Sound Design - and is involved in the European project Infopolis 2, concerned with Information Systems for Public transport Passengers. His research interests include Computer Science, Human-Computer Interaction (HCI), Electronics, Sound, Music, Multimedia, History and Archaeology. Mikael's home page can be found at http://www.ul.ie/~cscw/mikael.html

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