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Re: How se3 and ori is stored


Thanks Vaclav for the clear explanation.  Not to worry, renaming on Sunday night is a gd idea.  I believe everyone'll appreciate that u've thought about them.





> From: eudoxos@xxxxxxxx
> To: yade-users@xxxxxxxxxxxxxxxxxxx
> Date: Sun, 13 Dec 2009 21:28:34 +0100
> Subject: Re: [Yade-users] How se3 and ori is stored
> > Thanks, Vaclav. So, orientation is stored as [q0,q1,q2,q3] but
> > printed for the user as [ [axisX,axisY,axisZ],angle]. Now I
> > understand.
> > 
> > There is one more confusion. The following was from the archive. The
> > one in bold confuses me. Is se3 stored as [[X,Y,Z],[q0,q1,q2,q3]]? 
> Ah, ok. That is historical. XML serialization stores se3 as 7 floats (3
> for position, 3 for axis, 1 for angle) and till about last spring,
> python was (ab)using serialization to access attributes.
> You could still see this notation inside the xml files. With the advent
> of State, it is not State::se3 that is serialized (although it is what
> really holds the data), but rather pos and ori separately (which are
> merely references to se3::{position,orientation}); we wanted to get rid
> of se3, but it is more difficult than I thought, since quite often it is
> used to pass both position and orientation around; therefore it was kept
> in this way. I don't know of any se3 attribute that is serialized from
> the top of my head.
> In Python, se3 type doesn't exist at all, it is transparently converted
> from/to (Vector3,Quaternion) tuple.
> Cheers, Vaclav
> (PS as you might noted, I did some long-perpared renames a few moments
> back, hoping that Sunday night is the right moment; hope it doesn't
> conflict with what you do now.)
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