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Subject: Re: Find instant axis of rotation
Date: Thu, 29 Oct 2009 10:43:03 +0000 (UTC)
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Dear Henning Olsson!

> p0=[-199.177	399.997	172.887]';
> q0 = [-199.177	-400.003	172.872]';
> r0 = [-2479.583	244.996	225.422]';
> %points after
> p1 = [-199.056	399.997	172.048]';
> q1 = [-199.056	-400.003	172.034]';
> r1 = [-2479.425	244.996	226.179]';

What values do you expect?
I get:
  Angle: 0.000699
  Translation: -0.000261
  Helical axis: [-0.00178, 0.999998, 2.792e-5]
  Origin of axis: [-1397.32, -2.4959, -04475]
This set of values is not unique, e.g. all points on the axis can be used as origin. I've defined the point with the minimal distance to the global origin.

Please be aware, that the rotational angle of your example is tiny and rounding errors can dominate the result! There is no difference between a rotation around a point far away and a pure translation...

Jan