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Measuring a water vortex
like this one presents significant
difficulty, for a number of reasons,
chief amongst which is
obviously the pronounced ripple. The
errors worsen as the
vortex narrows. Nevertheless - with some
good will - we may
see a general conformityto a NULL path curve, and
to a
straight subNULL path curve.
Measurement here is even more problematic, as the ripple
is really a large wobble, which we may see from the severe
displacement of the axis, and there are many lesser ripples,
so we fit to the whole widths - the diameters - which combines
and averages the two profiles, to reduce the impact of all
these spuria.
The result is quite a good fit to path curves—in which the ripples
nevertheless remain quite visible.
These two show attempts to match the “double helix” ripples
and left profiles. Black spirals are “plan views” of spirohelices.
