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John M. Stevens
09-30-1995, 08:38 AM
> Date: Fri, 29 Sep 1995 11:05:53 SAST-2
> From: "Van Geems, B, Barbara, Ms"
> Subject: Re: Labelling of Co-ord axes
So the comments I
> am making on the subject of coordinate axes is from my working point
> of view and do not represent any right or wrong answers - especially
> as I have only recently begun the learning curve of biomechanics.

> the x-axis runs from left to right along the "flight-line" /
> baseline, i.e. the axis is horizontal increasing to the right,
> the y-axis is vertical, increasing upward,
> the z-axis is increasing positively toward one.
I hope this does not confuse the debate further on setting up
> coordinate axes standards.
> Barbara van Geems
> Department of Biomedical Engineering
> University of Cape Town Medical School

It would seem that the coordinate system you are used to is the same
system we were all trained in since early algebra. Therefore, it is,
I would propose, a universally accepted basic scientific system. Unless
I have woefully misunderstood the debate (please correct me if I am
wrong), the question seems to be in what anatomical position the
human body is to be represented in this coordinate system, i.e. is
the body to be upright (as we commonly represent it) or recumbant (as
in the CT scanner or in autopsy).

There is no logical reason why one position would be superior
to the other. But as a physician who uses biomechanical information about
my patients, I do see the majority of my patients in the upright posture.
And while I recognize the scientific need to represent motion along
these three axes, I have little need for it in practice since, regardless of
posture, I deal with flexion, extension, and translation of joints in
discussing problems with patients.

Discussing biomechanics and publishing findings between specialists
in that area should logically be done using an XYZ coordinate
system, but the folks that really use (or should be using) the
results of that information are the physicians, physical therapists,
and others directly involved in the practical application of the
research data. To adopt a coordinate system as a standard although
it is not in accord with the universal XYZ algebraic standard and not
harmonious with the typical upright posture of the human body will
only add to confusion in the translation of information from
researchers to the end-users, i.e. physicians. (For those who perform
their research on recumbant bodies, as in the CT scanner, it is a
simple matter to redefine the label on an axis to be compatible with
an upright presentation.)

John M Stevens (jstevens@texas.net)