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The team of Artis, LLC and the Harvard Prevention Research Center is under contract to the Centers for Disease Control and Prevention (CDC) to develop and test a system that measures human physical activity in an arbitrary area. The Smartmat system is comprised of hundreds of sensors for measuring pedestrian activity, a GPS for location of the device itself, a SmartMedia interface for data capture, a serial port interface, and a network management system that accumulates analog signals, performs analog to digital conversion, communicates digital data via an I 2C network using a specially designed protocol and compresses data before storing. The data are then processed by a microcontroller to translate sensor responses into pressure change boundaries, footfalls and ultimately paths permitting a pedestrian to be counted and their direction of travel recorded.
The analysis software performs several steps to compute a path from a series of footfalls. The paths are then counted and reported. The program first expands compressed data received from the data accumulator, isolates individual footprints, filters out high frequency noise, computes the print direction and speed, connects prints into paths, displays a summary of the results, and, optionally, writes an animated GIF image.
For single subjects (N=39), the False Alarm Rate (FAR – a measure of false positives) was 5.13%, and the Probability of Acquisition (PA – the probability of sensing a subject) was 100%. For multiple subjects crossing the Smartmat at a given time (N=108), FAR was 0.00% and PA was 91.74%, indicating that the Smartmat had a tendency to over-count single subjects and under-count multiple subjects. When no subjects were using the mat (e.g. it was turned on but nobody permitted to pass over it), it correctly reported zero counts. Finally, Smartmat rejected a non-human subject, a dog. The cumulative error rate (for all subjects) was 5.44%. This met the CDC goal set for the project, and Artis is proceeding with Phase II where the goal is a FAR of 1% and PA of 99%.
Highlights anticipated by Smartmat include:
- Automatic, no human observation required.
- Low cost compared with other surveillance means.
- Easy to set up and relocate.
- Resembles industrial carpet in appearance.
- Ruggedized and battery operable for outdoors use.
- Comes packaged with sophisticated traffic pattern analysis software.
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