Re: Question about PmPose in posemath.h

["Till Franitza" <xfa-at-isw.uni-stuttgart.de>]

Hallo!
Quaternions have nothing to do with roll,pitch yaw or euler angles!
They have to do with euler Parameters. Search for quaternions in the
internet. Quaternions have several advantages over angle representations.
They express the Orientation of an object by an axis of rotation and a
rotation about that axis. Eyler angles 0,0,0 all transform into Quaternions
1,0,0,0 quat.s is for normalization. The norm is 1. The whole derivation is
really complicated and i must admit that i do not fully understand it.
But i can USE quaternions. To transform from quat to rotation matrix you
have to use pmQuattorot or something. It is also used in genhexkins.c at the
beginning of the forward trafo.
Till
-----Ursprüngliche Nachricht-----
Von: Eding, Bert <b.eding-at-Nyquist.com>
An: Multiple recipients of list <emc-at-nist.gov>
Datum: Dienstag, 29. August 2000 09:26
Betreff: Question about PmPose in posemath.h


>
>
>I guess this question is for a Fred to answer.
>Lately I am diving, at least trying to, in Kinematics.
>My question is about the definition of the PmPose structure, it is defined
>as:
>
>typedef struct
>{
>  PmCartesian tran;
>  PmQuaternion rot;
>
>} PmPose;
>
>while PmQuaternion and PmCartesian are defined as:
>
>typedef struct
>{
>  double s, x, y, z;
>
>} PmQuaternion;
>
>typedef struct
>{
>  double x, y, z;
>
>} PmCartesian;
>
>
>My question 1):
>Is the order of rotations defined by the "s" value or how is this done?
>
>I expect that the PmPose is entended to unique define a robots position,
>I have an understanding problem with the definition of the rotation.
>It is clear that the order of rotation is important,
>rotate x, then y is different from rotating y and then x.
>
>The reason that I ask is that in another mathe library that I have the pose
>is
>defined as:
>
>typedef struct
>{ 
> VECTOR pos; 
> ORI ori; 
>} POSE;
>
>Here VECTOR is the same as PmCartesian, but ORI is defined as:
>typedef struct 
>{ 
> double e[3][3]; 
>} ORI;
>
>Here ORI is 
the rotation matrix, here I understand that the
>POSE structure does unique define the robots position, I do not understand
>this
>with the PmPose from the RCS-lib.
>
>
>My question 2):
>How can I convert from the PmQuaternion to a rotation matrix?
>
>Thanks in advance
>Bert Eding
>
>
>
>