07-20-1998, 03:11 PM
Gideon has asked for comments on his synchronisation method so here goes.

I first used the idea of employing the digitised data to synchronise two 16 mm
cameras in 1982. The method used a single point on the body (the left ankle)
to synchronise near the beginning and end of a movement on trampoline.
Details are in:-

Yeadon, M.R. 1984. The mechanics of twisting somersaults. PhD dissertation.
Loughborough University.

Subsequently I used two methods based on the data of all digitised points
on the body near the beginning and end of a jump to synchronise ski jumping
at the Calgary Olympics. I have used this method in a number of studies
of gymnastics dismounts but it is first described in:-

Yeadon, M.R. 1989. A method for obtaining three-dimensional data on ski
jumping using pan and tilt cameras. International Journal of Sport
Biomechanics 5, 2, 238-247.

Using all the digitised points on the body for all video fields (or film
frames) is an improvement over the methods which synchronise only at
the start and end of a movement. It is indeed possible to obtain RMS sync
errors of less than half a millisecond providing some points have
substantial velocity components perpendicular to the plane parallel to
the camera axes. Details will eventually be given in the paper below
when and if it is accepted.

Yeadon, M.R. and King, M.A. (submitted) A method for synchronising
digitised video data. Journal of Biomechanics.

M.R. (Fred) Yeadon

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