# [osg-users] How to scale rotations ?

J.P. Delport jpdelport at csir.co.za
Mon Jul 28 00:16:21 PDT 2008

```Hi,

I normally like to think about the heading, attitude and bank as just
rotations about certain axes. In osg you can make a quat using e.g.:

// angles in radians, yaw, pitch, roll
double y,p,r;

osg::Quat ori = osg::Quat(r, osg::Vec3(1,0,0),
p, osg::Vec3(0,1,0),
y, osg::Vec3(0,0,1));

Change the order/axes for your app. Try to do all the scaling using
quats. Either by multiplying them together, or changing the r,p,y values
in the code above.

jp

Janusz wrote:
> Dear all:
>
> Appreciate any answer on the topic:
>
> I am reading an orientation / rotation matrix info from a sensor, then
> visualizing the rotation of an object on screen with OSG. Given the
> matrix or the resulting quaternion I need to be able to scale the
> rotations independently, i.e.
>
> attitude_scale*attitude_angle
> bank_scale*bank_angle
>
> in order to be able to control them on its own or restrict the rotation
> to one angle only.
>
> I have written 2 functions. The first one converts a quaternion to the
> Euler angles, the other one does the opposite. In between the calls to
> the functions I am trying to scale the rotations or switch them on/off
> as needed.
>
> The results are not quite good, however, and I often get trapped in the
> famous "gimbal lock" as probably expected. :-)
>
> Q: Is there any other possibility to handle rotations on its own? Is
> there a way to do that without running the conversion, scaling, then
> converting back to quat ?
>
> All I have is the rotation matrix.
>
>
> Best regards,
> Janusz Goldasz
>
> --
> void getEulerFromQuat(osg::Quat q, double& heading, double& attitude,
> double& bank)
> {
>    double sqx = q.x()*q.x();     double sqy = q.y()*q.y();     double
> sqz = q.z()*q.z();
>
>    double t = q.x()*q.y() + q.z()*q.w();
>    if (t>0.49999)
>    {
>        heading = 2 * atan2(q.x(),q.w());
>        attitude = osg::PI_2;
>        bank = 0;
>    }
>    else if (t<-0.49999)
>    {
>        heading = -2 * atan2(q.x(),q.w());
>        attitude = - osg::PI_2;
>        bank = 0;
>    }
>    else
>    {
>        heading = atan2(2*q.y()*q.w()-2*q.x()*q.z() , 1 - 2*sqy - 2*sqz);
>        attitude = asin(2*t);
>        bank = atan2(2*q.x()*q.w()-2*q.y()*q.z() , 1 - 2*sqx - 2*sqz);
>    }
> }
>
>
>
>
> void getQuatFromEuler(double heading, double attitude, double bank,
> osg::Quat& q)
> {
> double c2 = cos(attitude/2);     double s2 = sin(attitude/2);     double
> c3 = cos(bank/2);     double s3 = sin(bank/2);
>    double c1c2 = c1*c2;    double s1s2 = s1*s2;
>
>    double w =c1c2*c3 - s1s2*s3;
>    double x =c1c2*s3 + s1s2*c3;
>    double y =s1*c2*c3 + c1*s2*s3;
>    double z =c1*s2*c3 - s1*c2*s3;
>
>    q = x; q = y;
>    q = z; q = w;
> }
>
> _______________________________________________
> osg-users mailing list
> osg-users at lists.openscenegraph.org
> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>

--
This message is subject to the CSIR's copyright terms and conditions, e-mail legal notice, and implemented Open Document Format (ODF) standard.
The full disclaimer details can be found at http://www.csir.co.za/disclaimer.html.

This message has been scanned for viruses and dangerous content by MailScanner,
and is believed to be clean.  MailScanner thanks Transtec Computers for their support.

```