[Rock-dev] RigidBodyState detecting invalid orientations

[Alexander Duda]

On 07/02/2012 09:08 AM, Felix Rehrmann wrote:
> Hi all,
>
> I would like to propose to have a seperate function like 
> isUnitQuaternion or similiar.
>
> One says that the rotation is not set,often because only position data 
> are transmitted.
> The other one is to check only the quaternion, which can also be 
> non-unit for numeric reasons.
Do you have a real use case for non-unit quaternions? I would favour to 
use unit quaternions for all base types as convention to remove another 
source of errors. In that case I would add the check insight isValidValue

Alex

>
> The user then would have the possiblity to decide what he wants to 
> know. Furthermore
> this function could have the accuracy as argument: bool 
> isUnitQuaternion (double accuracy = 1e-6).
> I would guess it could be hard to find a fixed value here. I would 
> consider some deviation from 1.0
> fine for further computation (e.g. like 0.9999something ).
>
> So long!
>     Felix
>
>
> Am 29.06.2012 18:43, schrieb Janosch Machowinski:
>> Uhm,
>>
>> fabs(ori.squaredNorm() -1) < 1e-6
>>
>> Just as an idea ;-)
>> Greetings
>>     Janosch
>>
>> On 29.06.2012 17:58, Javier Hidalgo Carrió wrote:
>>> On 06/29/2012 05:20 PM, Alexander Duda wrote:
>>>> On 06/29/2012 05:02 PM, Javier Hidalgo Carrió wrote:
>>>>> +1
>>>>> Since Orientation is a Eigen::Quaternion we could even use the 
>>>>> norm() method.
>>>>>
>>>>> Javier.
>>>>>
>>>>> Scalar 
>>>>> <http://eigen.tuxfamily.org/dox/classEigen_1_1QuaternionBase.html#a844358c46408e878e60c4026c52eb1e9> 
>>>>> norm 	( 	
>>>>> 	) 	const|[inline]|
>>>>>
>>>>> *Returns:*
>>>>>     the norm of the quaternion's coefficients 
>>>>>
>>>>> *See also:*
>>>>>     QuaternionBase::squaredNorm()
>>>>>     <http://eigen.tuxfamily.org/dox/classEigen_1_1QuaternionBase.html#a8699d72c996ca6cb4673e810fe3a616c>,
>>>>>     MatrixBase::norm()
>>>>>     <http://eigen.tuxfamily.org/dox/classEigen_1_1MatrixBase.html#a0be1b433c65ce9d92c81a4718daf54e5>
>>>>>
>>>>>
>>>>>
>>>> I think you do not gain so much from this functions as you will get 
>>>> a scalar which you have to sum anyway. Do you know if there is a 
>>>> function which checks if the quaternion is valid?
>>>>
>>> I don't know any valid method. Having no-normalized quaternion is 
>>> sometimes common (e.g, passing a quaternion through a EKF) and 
>>> normalization needs to be done.
>>>> fabs(ori.w()*ori.w()+ori.x()*ori.x()+ori.y()*ori.y()+ori.z()*ori.z()-1.0) 
>>>> < 1e-6
>>>>
>>> What should be the error threshold to define if a quaternion is 
>>> valid or not? Perhaps norm() does some round to 1.00...
>>>> Alex
>>>>> On 06/29/2012 04:53 PM, Alexander Duda wrote:
>>>>>> Hi,
>>>>>>
>>>>>> the base type samples::RigidBodyState has a function to check if the
>>>>>> orientation is valid.
>>>>>> At the moment it only checks if the values of the quaternion
>>>>>> representing the orientation are different to NaN.
>>>>>>
>>>>>> I propose that we also add a check that the quaternion is an unit
>>>>>> quaternion because otherwise wrongly initialised orientations might lead
>>>>>> to strange transformation matrices and vanishing objects in OSG.
>>>>>>
>>>>>> Any opinions?
>>>>>>
>>>>>> Alex
>>>>>>
>>>>>>           static bool isValidValue(base::Orientation const&  ori)
>>>>>>           {
>>>>>>               return !base::isNaN(ori.w())&&
>>>>>>                   !base::isNaN(ori.x())&&
>>>>>>                   !base::isNaN(ori.y())&&
>>>>>>                   !base::isNaN(ori.z())&&
>>>>>>
>>>>>> ori.w()*ori.w()+ori.x()*ori.x()+ori.y()*ori.y()+ori.z()*ori.z()-1e6<  1;
>>>>>>           }
>>>>>>
>>>>>
>>>>>
>>>
-- 
Dipl.-Ing. Alexander Duda
Unterwasserrobotik

DFKI Bremen
Robotics Innovation Center
Robert-Hooke-Straße 5
28359 Bremen, Germany

Phone: +49 (0)421 178-456620
Fax:   +49 (0)421 178-454150
E-Mail: alexander.duda at dfki.de

Weitere Informationen: http://www.dfki.de/robotik
-----------------------------------------------------------------------
Deutsches Forschungszentrum fuer Kuenstliche Intelligenz GmbH
Firmensitz: Trippstadter Straße 122, D-67663 Kaiserslautern
Geschaeftsfuehrung: Prof. Dr. Dr. h.c. mult. Wolfgang Wahlster
(Vorsitzender) Dr. Walter Olthoff
Vorsitzender des Aufsichtsrats: Prof. Dr. h.c. Hans A. Aukes
Amtsgericht Kaiserslautern, HRB 2313
Sitz der Gesellschaft: Kaiserslautern (HRB 2313)
USt-Id.Nr.:    DE 148646973
Steuernummer:  19/673/0060/3

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.dfki.de/pipermail/rock-dev/attachments/20120702/e466ace4/attachment-0001.htm