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Hello BIOMCH-L readers,
I am working in gait biomechanics and am writing code to fill in missing
data from streams of 3-dimensional co-ordinate data. Our system generates
0 values in the co-ordinate file when a marker is out of camera-system
view. Thus far I have tried polynomial curve fitting of varying orders
based on datapoints prior to the missing value, and extrapolating the
value. This method only met with limited success as the movement in
different axes has behaviour of different (polynomial curve) orders. If
the gap of missing markers is too large, the extrapolated point estimation
diverges greatly, depending on the order of the polynomial fit.
The second method I have tried is to fit a cubic spline to datapoints
prior to the missing point in question. This is met with limited success.
Questions:
1. Most, if not all interpolation procedures that I know of require
equally spaced data; thus if there is a gap in ones dataset, a polynomial
curve or spline cannot be fit to the dataset! Could anyone confirm this
statement?
2. I would like to know from individuals that use movement data (gait and
others), what types of extrapolation or curve-fitting procedures are
commonly being used.
3. Does anyone know of a 3-dimensional spline technique whereby one can
utilize all x,y,z co-ordinate data to extrapolate the next point(s)!
I will post a follow-up with replies.
Thanks
Alan Morris
Research Engineer - Gait Laboratory
Bloorview MacMillan Centre
350 Rumsey Road
Toronto, Ontario
CANADA
M4G-1R8
Tel (416) 425-6220 x3508
Fax (416) 425-1634
email morrisa@ecf.utoronto.ca
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I am working in gait biomechanics and am writing code to fill in missing
data from streams of 3-dimensional co-ordinate data. Our system generates
0 values in the co-ordinate file when a marker is out of camera-system
view. Thus far I have tried polynomial curve fitting of varying orders
based on datapoints prior to the missing value, and extrapolating the
value. This method only met with limited success as the movement in
different axes has behaviour of different (polynomial curve) orders. If
the gap of missing markers is too large, the extrapolated point estimation
diverges greatly, depending on the order of the polynomial fit.
The second method I have tried is to fit a cubic spline to datapoints
prior to the missing point in question. This is met with limited success.
Questions:
1. Most, if not all interpolation procedures that I know of require
equally spaced data; thus if there is a gap in ones dataset, a polynomial
curve or spline cannot be fit to the dataset! Could anyone confirm this
statement?
2. I would like to know from individuals that use movement data (gait and
others), what types of extrapolation or curve-fitting procedures are
commonly being used.
3. Does anyone know of a 3-dimensional spline technique whereby one can
utilize all x,y,z co-ordinate data to extrapolate the next point(s)!
I will post a follow-up with replies.
Thanks
Alan Morris
Research Engineer - Gait Laboratory
Bloorview MacMillan Centre
350 Rumsey Road
Toronto, Ontario
CANADA
M4G-1R8
Tel (416) 425-6220 x3508
Fax (416) 425-1634
email morrisa@ecf.utoronto.ca
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To unsubscribe send UNSUBSCRIBE BIOMCH-L to LISTSERV@nic.surfnet.nl
For more information: http://www.kin.ucalgary.ca/isb/biomch-l.html
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