[ODE] quat to eulerXYZ

[Patrick Enoch]

So its impossible to convert the angular vel from one euler to the  
other?
or maybe someone has a patch so i can give the ang. vel. in quats?

Patrick


On 25. Jun 2005, at 18:11 Uhr, Bill Sellers wrote:


> Dear Patrick,
>
> You've just hit on the reason why most people don't use Euler  
> coordinates any more - they are discontinous so a 3D angle that is  
> very close to another 3D angle can have a very different Euler  
> coordinate. It all happens when one of the angles is close to 90  
> degrees. This (as you can imagine) leads to horrible instability  
> (and there's a mechanical analogue called gimbal lock if you are at  
> all interested). Matrix representations are similarly (but not as  
> catastrophically) unhelpful but Quaternions are nicely well behaved  
> (except for the bit where the negative of a quaternion equals the  
> positive).
>
> The joys of 3D rotations.
>
> Cheers
> Bill
>
> On Saturday, June 25, 2005, at 04:04  pm, Patrick Enoch wrote:
>
>
>
>> Hello all,
>>
>>
>> I am having problems with angular velocities. currently i am  
>> interfacing ODE to another program which uses eulerZXY.
>> so if i have a body with eulerZXY angular velocity, I need to  
>> convert it to ODEs eulerXYZ.
>> i am using quaternions as the interface, which looks like this:
>>
>> prog eulerZXY at time A and B -> quats at time A and B -> ODE  
>> eulerXYZ at time A and B
>> (angular velocity is difference between eulers divided by (B-A))
>>
>> BUT:
>> when converting quats -> eulerZXY there are jumps in the  
>> conversion. for example:
>>
>> euler ZXY (0,89,0) -> eulerXYZ (89,0,0)  (works fine)
>> euler ZXY (0,91,0) -> eulerXYZ (180,-91,180) (pretty far away from  
>> the above)
>> (values as far as i remember. but i think the prob is clear. the  
>> difference should be small, but the resulting
>> angular velocity is very big. conversion depends on into which  
>> quadrant the rotation points, its an
>> unsteady function. )
>>
>> anyone knows a quat -> euler converter, which i can tell to give  
>> me values "near" to another triple?
>>
>>
>> Patrick
>>
>> _______________________________________________
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>> http://q12.org/mailman/listinfo/ode
>>
>>
>>
> --
> Dr. Bill Sellers, Editor Primate Eye   Email: W.I.Sellers at lboro.ac.uk
> Department of Human Sciences           Tel:   UK (0) 1509 228228
> Loughborough University                Fax:   UK (0) 1509 223941
> Loughborough LE11 3TU UK               http://mac-huwis.lboro.ac.uk/ 
> ASL/
>
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>
>
>