Matthias Ferch schrieb:
Matthias Ferch schrieb:
Andreas Goebel schrieb:
Matthias Ferch schrieb:
in my app, the user can enter 3 angles in degrees (float AngleX,
AngleY, AngleZ) in text controls to set the rotation of a
PositionAttitudeTransform. the entered values are then processed
like this:
float qx = (AngleX*PI)/180.0f;
float qy = (AngleY*PI)/180.0f;
float qz = (AngleX*PI)/180.0f;
MeshTransform->setAttitude( Quat(qx, Vec3(1.0f, 0.0f, 0.0f), qy,
Vec3(0.0f, 0.0f, 1.0f), -qz, Vec3(0.0f, 1.0f, 0.0f)) );
the user can alternativly simply rotate the
PositionAttitudeTransform with the mouse. so i need to get the
updated rotation values to update my text controls. my question is
now, how can i extract these values back from the transform (in
degrees)? yeah i suck at maths :D
thanks in advance!
_______________________________________________
Hi,
it´s not that easy and no shame to ask.
I have the nice book "Geometric toosl for computer graphics", and
there is the following solution:
- convert the quat to a matrix. Lets assume your matrix is r00, r01,
r02 (first row), r10, r11, r12 (second row) and so on (convert this
to your needs)
thetaY = asin(r02);
if (thetaY < PI/2.0) {
if (thetaY > -PI /2.0) {
thetaX = atan2(-r12, r22);
thetaZ = atan2(-r01, r00);
} else{
//solution is not unique!
thetaX = -atan2(r10, r11);
thetaZ = 0;
}
}else{
thetaX = atan2(r10, r11);
thetaZ = 0;
}
atan2 is defined in math.h
Please let me know if it works. You will have to calculate back the
values do degrees, of yourse. The solution is not unique, and I
don´t know if you have the ordering x, y, z.
Regards,
Andreas
oha ok, thank you! one problem though, i created a matrix from the
quat, but how can i access the members of a matrix in osg? the []
operator is not defined..
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ok, i got it like this now:
osg::Quat attitude =
parent_data->MeshTransform->getAttitude();
osg::Matrix matrix = osg::Matrix( attitude );
float r02 = matrix(0, 2);
float r12 = matrix(1, 2);
float r22 = matrix(2, 2);
float r01 = matrix(0, 1);
float r00 = matrix(0, 0);
float r10 = matrix(1, 0);
float r11 = matrix(1, 1);
float thetaX, thetaY, thetaZ;
thetaY = asin( r02 );
if( thetaY < PI/2.0 )
{
if( thetaY > -PI/2.0 )
{
thetaX = atan2( -r12, r22 );
thetaZ = atan2( -r01, r00 );
}
else
{
thetaX = -atan2( r10, r11 );
thetaZ = 0;
}
}
else
{
thetaX = atan2( r10, r11 );
thetaZ = 0;
}
VectorX->SetValue( -(thetaX*180.0f)/PI ); // why do
i need a minus here?
VectorY->SetValue( -(thetaZ*180.0f)/PI );
VectorZ->SetValue( (thetaY*180.0f)/PI );)
It looks well, except that I would use float& or use the matrix directly.
does this look reasonable? well, it works correctly, if i enter values
for VectorX and VectorY, but keep VectorZ = 0.0f. it also works if I
enter a value for VectorZ, but keep VectorX = 0.0 and VectorZ = 0.0.
but as soon as enter values for VectorZ and either ValueX or ValueY,
the values are not given back correctly. trotzdem vielen dank schonmal :P
As I said, the values of thetaX, thetaY and thetaZ are not uniquely
determined (eindeutig definiert) by the rotation. So you might get back
different values from what you entered, but it should be the same rotation.
Regards und viele Grüße,
Andreas
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--
Andreas Goebel
Visit http://www.raumgeometrie.de to take a look at
Archimedes Geo3D, a program for dynamic geometry
in three dimensions!
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