| Re: [eigen] precision loss after conversion from rotation matrix to quaternion and back |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] precision loss after conversion from rotation matrix to quaternion and back
- From: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>
- Date: Mon, 14 May 2012 22:13:30 +0200
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Hi,
I guess this is because your initial matrix is not perfectly unitary.
You can orthogonalize it with, e.g.:
A = A.householderQr().householderQ();
cheers,
Gael.
On Mon, May 14, 2012 at 9:23 PM, Tobias Langner
<tobias.langner@xxxxxxxxxxxx> wrote:
> Hello all,
>
> So here is my problem:
>
> I have this rotation matrix (Scalar type double):
>
> 0.124564 -0.800873 0.584451
> -0.971925 0.0176983 0.231399
> -0.19596 -0.597765 -0.777352
>
> Then I convert it to a Quaternion (Scalar type double) using the
> constructor. The quaternion coefficients (x,y,z,w) are:
> 0.686334 -0.645749 0.14151 -0.302026
>
> Finally I convert the Quaternion back to a rotation matrix using the
> function toRotationMatrix(), which yields a slightly different matrix:
>
> 0.125967 -0.80092 0.584312
> -0.971878 0.0178409 0.231823
> -0.195821 -0.597341 -0.776092
> 0.686334 -0.645749 0.14151 -0.302026
>
> As you can see some numbers differ on the third significant digit, which
> cannot be explained by floating point rounding errors. So where does it come
> from? If I repeat the procedure the rotation matrix will not differ again..
> It changes only on the first forth-and-back conversion.
> I'd appreciate any help.
>
> Best regards,
>
> Tobias
>
>
>
>
>
>