Hi Oscar,
In Simulink R2024b, I notice that in the ‘6DoF (Quaternion)’ block in Aerospace blockset, the quaternion representation ( q ) is not directly available. It had to be calculated by transforming the Euler angle output ( 
) of the ‘6DoF (Quaternion)’ block using the ‘Rotation Angles to Quaternion’ block.
) of the ‘6DoF (Quaternion)’ block using the ‘Rotation Angles to Quaternion’ block. Whereas in R2025a, the Euler angle to quaternion transformation has been inbuilt into 6DoF (Quaternion) block with the quaternion representation provided as output at ( q ) port.
I too have observed the jump in the quaternion representation when transforming Euler angles explicitly in the R2024b version, whereas the output ( q ) in R2025a version seems continuous.
There is a mathematical reason behind the jump, that is, the quaternion representation of a rotation is not unique. Both quaternions ( q ) and ( -q ) produce the same rotation matrix or have the same effect when rotating a vector. This is called the 'double cover' property of the quaternions. Now, depending on how a transformation algorithm handles the non-uniqueness in representation, the quaternion output may be continuous or may have discontinuities. Nevertheless, both outputs are correct and represent the same rotation.
The ‘Look under mask’ functionality for 6DoF (Quaternion) block is disabled for me as well in R2025a version. Hence, I don’t know the exact details of how the discontinuity is being resolved in R2025a.
For more information on the 'double cover' property, refer the below link.
Additionally, you can reach out to MATLAB Technical support on the below link. https://supportcases.mathworks.com/mwsupport/s/casetypeselection?language=en_US&c__caseParameter=productusage&s_tid=srlp_product
