[Bf-funboard] Euler for animator, Quaternions for Blender

[Robert Wenzlaff (AB8TD)]

On Tuesday 15 May 2007 20:47, Roger wrote:
> I'm probably way off track and apologise for this  but could a user defined
> axis bordered by a yaw circle.
> be set up for a particular object or bone to be rotated around, then the
> roll, pitch and yaw could be relative to the user defined axis instead of
> x,y,z axes then be referred to as roll, pitch and yaw.
> Gimbal lock then couldn't exist.
>   A user defined axis could only have pitch and yaw regardless of
> orientation and it's centre of pitch could be user defined anywhere along
> the axis, the object to which it is applied would have roll.
> I dont know if I am explaining this sufficiently, apologies for that.

Those local angles have to be measured against something.
An object doesn't have an inherent "level flight" condition w/o knowing where 
the XY plane is.  A "user defined axis" is just some combination of the 
global axises.

You may be able to avoid the singularity in your objects frame of reference, 
but Blender needs to know where the object is in global space.

If you choose the global X axis as your reference, pitch 90 degrees, roll 90 
degrees, and pitch -90 degrees. That is the same as a yaw of 90 degrees.  
Given 2 endpoints, Blender has to guess the points in between.  For regular 
objects, Blender uses Eulers and chooses the shortest path.  This is almost 
always correct and easy to fix if not (add another key).  

With bones, their interactions and constraints make it not so easy to find 
the "right" path from Rotation A to Rotation B.  Quats internally make some 
of the calculations easier, too.  But it's easier to convert back-and-forth 
and use tricks to solve the sticky bits than it is for the user to edit the 
Quats directly.

-- 
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Robert Wenzlaff  rwenzlaff at soylent-green.com

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