Reliability of a Real Time Optical Navigation Feedback System for Training Alpine Skiers Richard Kirby, Advanced Racing Computers Troy Flanagan, Director of Sport Science, USSA Alan Schönberger, Ski Studio

Introduction “When performance is measured performance improves and when performance is measured and reported the rate of performance improvement accelerates.” -- Thomas S. Monson New tool requires validation of reliability of data.

PROBLEM: DETERMINE RELIABILITY OF VLINK DATA

VLINK DEVICE

HOW IT WORKS Click here to play video

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vLink vs. GPS Standard GPS samples at 1 Hz. At 20m/s that is a sample every 20 meters. dGPS samples at 20 Hz or once every meter. vLink samples at 6500 Hz or once every 3 mm.

15.2 m/s 0.09° 16.0 m/s 0.52° 15.6 m/s 0.19° 16.3 m/s 0.21° 16.1 m/s 0.20° 16.0 m/s 0.07° 16.2 m/s 1.16° 15.5 m/s 1.12° 15.7 m/s 0.06° 16.0 m/s 0.03° 15.7 m/s 0.41° Inside ski came off edge too soon here… … causing Will to be thrown into air, becoming un-aerodynamic and loosing 0.6 m/s.

HOW CONFIDENT ARE WE THAT 16.9 M/S IS FASTER THAN 16.7 M/S AS MEASURED BY THE VLINK? Tracking Skiers with the vLink

Accuracy vs. Reliability Accurate and reliable Reliable, requires correction to be accurate Low reliability

Tests Accuracy –CNC Mill Test Reliability –Sled Test on Snow –Carpet Test

Mill Test CNC Mill Silica Paper to simulate snow surface Controlled Distance = 5 m N = 12 Mean = 5.00 meters SD = 8 mm Typical error = 0.22%

SLED TEST EXPERIMENT SETUP On snow

SLED TEST RELIABILITY RESULTS Typical error = 1.57% N = 35

Sled Test Issues Soft snow conditions made repeatability difficult. Sled frame unstable as snow softened. Data showed non-random errors - distances decreased consistently test after test. Questioned accuracy setup vs. data accuracy.

RELIABILITY STUDY 2

RELIABILITY STUDY RESULTS Typical Error = 0.37% N=35

CONCLUSIONS Due to the instability of the on-snow test fixture it is difficult to say what part of the error was the vLink and what part was the experimental setup. However, the measured typical on-snow error of 1.6% would suggest that one would typically be within 0.3m/s of the correct speed at GS speeds. However, the experimental setup needs to be improved for valid results. Carpet tests suggests that the resolution could be better than 0.1 m/s at a speeds of 20 m/s. Technology capable of 0.05 m/s resolution

Reliability of a Real Time Optical Navigation Feedback System for Training Alpine Skiers Richard Kirby, Advanced Racing Computers Troy Flanagan, Director of Sport Science, USSA Alan Schönberger, Ski Studio

Support Slides

Filtering Required on Snow

Filtering method Holes or pockets in snow

Filtering introduces error when between digital values Actual Speed Measured Speed Resolution