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I would like to determine Euler angles according to the following example.

My example:

I have the three vectors in an original set of axes:

r1e = {-0.517853, 0., -0.759239}
r2e = {-0.517853, 0., 0.759239}
r3e = {0.0647316, 0., 0.}

And after expressing them in a new reference frame they obtain the following components:

rt1e={0.310733, -0.358839, -0.786917}
rt2e={0.690333, 0.298661, 0.527983}
rt3e={-0.0625667, 0.00376111, 0.0161833}

In reality, I know the Euler angles to be $(30,60,120)$ degrees. How can I get Mathetmatica to give me this?

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  • $\begingroup$ Have you tried EulerAngles? $\endgroup$
    – Henrik Schumacher
    Commented Jan 6, 2019 at 18:09
  • $\begingroup$ That command won't work, as the rotation matrix itself is not known. Only the two vectors. $\endgroup$
    – Spherical Cow
    Commented Jan 6, 2019 at 18:10
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    $\begingroup$ In general, a rotation matrix is not uniquely defined by the action on a single vector... $\endgroup$
    – Henrik Schumacher
    Commented Jan 6, 2019 at 18:12
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    $\begingroup$ What I tried to say: If you prescribe a pair $u$ and $v$ of same length $\neq 0$ in $\mathbb{R}^3$, then there will be a one-parameter family of rotations (and thus a one-parameter family of Euler angles) that map $u$ to $v$. So, it is as it is: Your problem is underdetermined. $\endgroup$
    – Henrik Schumacher
    Commented Jan 6, 2019 at 18:18
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    $\begingroup$ "I actually have 3 vectors" - by this, do you mean the three vectors before and after being transformed by some rotation matrix? If so, please look at FindGeometricTransform[], which can be used with EulerAngles[]. $\endgroup$
    – J. M.'s missing motivation ♦
    Commented Jan 6, 2019 at 18:29

1 Answer 1

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As noted, you can use FindGeometricTransform[] in tandem with EulerAngles[]:

r = {{-0.517853, 0., -0.759239}, {-0.517853, 0., 0.759239}, {0.0647316, 0., 0.}};
rt = {{0.310733, -0.358839, -0.786917}, {0.690333, 0.298661, 0.527983},
      {-0.0625667, 0.00376111, 0.0161833}};

fg = FindGeometricTransform[r, rt];

EulerAngles[Drop[TransformationMatrix[Last[fg]], -1, -1]]/°
   {60.0048, 30.0019, 120.}
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