[osg-users] How to scale rotations ?
jpdelport at csir.co.za
Mon Jul 28 00:16:21 PDT 2008
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
osg::Quat ori = osg::Quat(r, osg::Vec3(1,0,0),
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.
> 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.
> heading_scale*heading_angle, heading_scale=<0,1>
> 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.
> Appreciate any answer/advice or pointing me in the right direction.
> 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;
> 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 c1 = cos(heading/2); double s1 = sin(heading/2);
> 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;
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