[ODE] Naive Pitch/Roll/Yaw rotation questions

[john rieffel]

Thanks!

Gabriel's advice was particularly useful.   The difficulty with
"letting the physics take care of it" is that my object is disabled,
and doesn't interact with the environment other than moving around 
(it's not really an airplane, it's more like a print-head, or LOGO
turtle, if you must know).  I need it to move through discrete
portions of the space, and to send it roll/pitch/yaw commands.

Here's what I've got for Yaw:

// make the local rotation
dQuaternion localQ;  
dQFromAxisAndAngle(localQ,0,1,0,rot_angle*M_PI/180);

//get the global rotation
const dReal *globalQ = dBodyGetQuaternion(turtle.body);
dQuaternion newQ;

//multiply them and set the result as the new body quaternion
dQMultiply0(newQ,globalQ,localQ);
dBodySetQuaternion(turtle.body,newQ);

And for pitch, the only change is to the localQ:

dQFromAxisAndAngle(localQ,1,0,0,rot_angle*M_PI/180);

and for roll:

dQFromAxisAndAngle(localQ,0,0,1,rot_angle*M_PI/180);

This seems to work great!  Again, thanks gabriel!

Now - howabout the inverse problem, of sorts: given an object's
quaternion, how do I find which global axis is currently the object's
"local" roll axis?

Thanks!
jr







On Tue, 15 Mar 2005 18:48:48 +0100, Anders Olofsson
<anders.olofsson at biologigrand.ac> wrote:
> Let the physics take care of rotation, dont call dBodySetRotation more than to
> initialize your bodies. Roughly speaking, if you for example want to roll your
> aircraft add an "up" force on one wing and a "down" force on the other
> wing. Thats
> what I do anyway.
> 
> --Anders Olofsson
> 
> At 17:25 2005-03-15, john rieffel wrote:
> >I'm comfortable using dBodySetRotation and dRFromAxisAndAngle in order
> >to rotate bodies in the global reference frame, but I'm stumped about
> >how to rotate objects relative to their own frame of reference.  I'm
> >sure that it's a simple matter of quaternion arithmetic, but it eludes
> >me.(kicking myself for never having taken any aero/astro classes, or
> >graphics classes for that matter).
> >
> >Imagine, for instance that my body is an airplane - I'd like it be
> >able to get it to pitch/yaw/roll.  To make things even easier, I only
> >ever want it to pitch/roll/yaw over a 90 degree angle.   For instance,
> >if the object's current roll axis is the "z" axis, and its yaw axis is
> >the "y" axis, then I want a +90 degree yaw to place its roll axis on
> >the x axis.
> >
> >thanks,
> >jr
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>