# [Bf-committers] Curve normal calculation

Giuseppe Canino jojospino at hotmail.com
Thu May 24 22:43:13 CEST 2007

```Hi,I think that user defined normal could be very useful,maybe it could be
cool if this vector can be used in python for scripting stuff(animating the
vector over time).I hope you can succeed in this,I need that for my hair
modelling techiniques
bye
Renderdemon

>From: "Ben Batt" <benbatt at gmail.com>
>Reply-To: bf-blender developers <bf-committers at blender.org>
>To: bf-committers at blender.org
>Subject: [Bf-committers] Curve normal calculation
>Date: Fri, 25 May 2007 03:29:12 +1000
>
>Hi all,
>I'm currently working on fixing curve normal calculation in Blender
>(to eliminate the curve twisting problem) using the torsion minimizing
>method outlined in:
>http://www.cs.auckland.ac.nz/~burkhard/Lectures/715S2C_2006/CalculationOfReferenceFrames.pdf
>(basically you choose a starting normal and then iterate along the
>curve in small steps, rotating the normal by the rotation from the old
>tangent to the new tangent at each step). I'm fairly happy with the
>results so far:
>http://i201.photobucket.com/albums/aa206/artificer_blender/curvenormals01.png
>
>This works reasonably well, but the issue of choosing a starting
>normal remains. The current method I'm using is just to choose a
>normal that is perpendicular to the tangent at the start of the curve,
>and as close to the positive Z axis ("up") as possible. If the
>starting tangent is vertical, the normal is set to be the positive X
>axis. This is not really an optimal solution, so I'd like to find a
>better one.
>
>One possibility I thought of was to give each curve a preferred normal
>specified as a vector, and allow the user to rotate this vector
>arbitrarily. The starting normal would then be the vector closest to
>the preferred normal while still being perpendicular to the starting
>tangent.
>
>discuss this problem?
>
>Thanks,
>Artificer
>
>
>
>
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>
>
>

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