View Full Version : Data filtering and differentiation

Robert Newton
02-02-1993, 04:55 AM
Dear fellow networkers,

I am developing a research project which involves the use of a rotary encoder
to provide displacement data to a resolution of 0.5 mm in 3.0 m at a frequency
of 500 Hz. I wish to derive velocity and acceleration data and have been using
a Butterworth filter for smoothing and differentiation of kinematic data which
is essentially parabolic in path. I would be most appreciative of any help
that can be provided as to:

1. Is the Butterworth a suitable filter or is there a better
alternative? I believe I have implemented a 4th order Recursive Butterworth?

2. Can anyone tell me what coefficients I should use for the terms in
the filter to produce a given cutoff frequency or is there a reference which
would list such information?

3. Can anyone direct me to a good review on data filtering in
biomechanics? In particular I need information on the actual
smoothing/differentiation algorithms. Code examples in C, Fortran etc would be
very helpful.

4. I would appreciate it if anyone could email me sample source code
of any smoothing/differentiation routines.

Thankyou in advance for any assistance that you can provide. It is
greatly appreciated.
Robert Newton Internet: rnewton@loki.une.oz.au
Lecturer in Biomechanics ACSnet: rnewton@loki.une.oz
University of NewEngland,
Northern Rivers Phone: +61 (066) 203762
P.O. Box 157
Lismore NSW Australia