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Topic: Euler Angle Order convertion
Replies: 3   Last Post: Jun 25, 2009 2:33 PM

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Dave Rudolf

Posts: 37
Registered: 10/3/05
Re: Euler Angle Order convertion
Posted: Jun 25, 2009 2:33 PM
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Anyone else have problems getting Ken Shoemake's code working? Eberly's formulas work fine, though I like the way Shoemake has packaged things, and how it handles a non-static ("rotating") frame of reference -- if only I could get it to work. It seems to be decomposing the rotations in the wrong order. Here's my simple test case that breaks:

// Create a rotation of 90 degrees about a diagonal axis
Quat q = AxisAngle( Vector( 1, 1, 1 ), M_PI * 0.5 );

// Convert to ZXY euler angles with static frame
int enc = EulOrdZXYs;
EulerAngles ea = Eul_FromQuat( q, enc );

// Generate quaternions for each indivudual axes
Quat qx = AxisAngle( Vector( 1, 0, 0 ), ea.x );
Quat qy = AxisAngle( Vector( 0, 1, 0 ), ea.y );
Quat qz = AxisAngle( Vector( 0, 0, 1 ), ea.z );

// Combine the individual rotations
const Quat qAct = qy * qx * qz;

If I print out the the expected quaternion and the actual one, I get two different rotations:

q (0.707107 0.408248 0.408248 0.408248)
qAct (0.707107 0.523699 -0.243049 0.408248)

However, if I combine the individual rotations in ZYX order, it all works fine:

q (0.707107 0.408248 0.408248 0.408248)
qAct (0.707107 0.408248 0.408248 0.408248)

I presume Shoemake's code actually does work, since lots of people cite it. So, any thoughts as to what I might be doing wrong?

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