[SciPy-User] The different results given by scipy and https://quaternions.online/ when converting Euler angles to Quaternion representation.

[Hongyi Zhao]

On Wed, Oct 28, 2020 at 4:29 PM Guillaume Gay <guillaume at damcb.com> wrote:
>
> Hi, Hongyi,
>
>
> This seems to have to do first with extrinsic vs intrinsic order, (the
> website seems to assume intrinsic angles). Thus with "XYZ" as first
> argument, the result are still different but that difference is
> consistent (which is not the case for e.g. `r = R.from_euler('xyz', [30,
> 45, 30], degrees=True)` which gives different values all together on
> your website / with scipy.
>
>
> r = R.from_euler('XYZ', [90, 45, 30], degrees=True)
>
> r.as_quat()
>
> array([0.70105738, 0.09229596, 0.43045933, 0.56098553])

I also find another website located at
<https://www.onlineconversion.com/quaternions.htm> for doing the
similar job. The results given by this website is as follows for the
Euler angles in degrees [90, 45, 30]:

0.560985526796931
0.43045933457687935
-0.560985526796931
0.43045933457687935

As you can see, this result is different from the ones obtained by
both extrinsic and intrinsic order of scipy shown as following:

extrinsic: [0.7010573846499779, 0.5609855267969309,
0.4304593345768794, -0.09229595564125723]
intrinsic: [0.560985526796931, 0.7010573846499778,
0.09229595564125731, 0.43045933457687935]


The codes used by me is as following:

from scipy.spatial.transform import Rotation as R
from squaternion import Quaternion

euler_angle = [90, 45, 30]

q = Quaternion.from_euler(euler_angle[0], euler_angle[1],
euler_angle[2], degrees=True)

extrinsic_r = R.from_euler('xyz', euler_angle[:], degrees=True)
intrinsic_r = R.from_euler('XYZ', euler_angle[:], degrees=True)

extrinsic_quat = extrinsic_r.as_quat()
intrinsic_quat = intrinsic_r.as_quat()

sq_quat = []
sq_quat.extend([q.w, q.x, q.y, q.z])

ex_quat = [extrinsic_quat[3]]
ex_quat.extend(extrinsic_quat[:3])

in_quat = [intrinsic_quat[3]]
in_quat.extend(intrinsic_quat[:3])

print(sq_quat)
print(ex_quat)
print(in_quat)


Regards,
HY

>
> the result is now a permutation away from what the website says.
>
>
> I'd test with 'obvious' cases to get to the bottom of that, but I mostly
> think one should trust scipy to do "the right thing" as it has had more
> scrutiny than the website.
>
>
> Hope this helps
>
>
> Le 27/10/2020 à 14:19, Hongyi Zhao a écrit :
> > Hi,
> >
> > I try to convert between Euler angle and Quaternion representations.
> > But I obtained different results when using scipy and the online
> > converter (https://quaternions.online/). See following for detailed
> > info:
> >
> > The results obtained from scipy:
> >
> > In [14]: from scipy.spatial.transform import Rotation as R
> >
> > In [15]: r = R.from_euler('xyz', [90, 45, 30], degrees=True)
> > In [17]: r.as_quat()
> > Out[17]: array([ 0.56098553,  0.43045933, -0.09229596,  0.70105738])
> >
> > The results given by the online converter (https://quaternions.online/):
> >
> >   w: 0.561
> >   x: 0.701
> >   y: 0.092
> >   z: 0.430
> >
> > Any hints for this problem will be highly appreciated?
> >
> > Regards,
> > HY
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-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao at gmail.com>
Theory and Simulation of Materials, Xingtai Polytechnic College
NO. 552 North Gangtie Road, Xingtai, China