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RE: [V8i VBA] Finding Tangent Vector of point on an element

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Afternoon Jon,

[quote user="Jon Summers"]

I confirm that the VBA method EvaluatePointTangent doesn't work as expected.  The computed point does not correspond to parameter u except when u = 0 and u = 1.  At intermediate points the computed point is at a greater distance along the B-spline than expected.

[/quote]

That's good that you found the same as me but bad that the function doesn't work as you believe it should. I guess this leaves me with 2 questions:

  1. Are you familiar with any other Point3D functions which might yield the necessary information? I vaguely recall a post from DanPaul mentioning EvaluatePointFrame and I tried testing it but I am not sure how to make use of the Frenet Frame.
  2. Is there any alternative non-bspline methods that would can calculate the perpendicular CCW rotation?

[quote user="Jon Summers"]

The computed tangent, by the way, is not a point.  It's a direction vector.  A Point3d is a convenient receptacle for the values, not to be taken literally.

[/quote]
Thanks for clearing that up. Its been 20 years since I last learned vectors so I've spent some time this morning getting familiar with them again.

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