[Sidefx-houdini-list] Quaternons and Lag CHOP

zhang xiao zhangxiao6776 at gmail.com
Thu Sep 1 17:44:13 EDT 2011


hi , Pablo, check out this thread, it has a spherical interpolation
setup for the quaternion, the reason i bring that up is the component
of quaternion is not the same as vector3 component.
http://forums.odforce.net/index.php?/topic/12707-learning-about-quaternions/

2011/9/1 Pablo Giménez <pablogipi at gmail.com>

> 2011/9/1 Edward Lam <edward at sidefx.com>
>
> > Have you tried changing the Method to "Lag Magnitude" ?
> >
> Thanks Edward.
> I tried it but I got the same result, so I guess the Lag is not detecting
> my
> vectors components channels.
> My rotation channels are in the next form: rot[xyzw]*.
> So I have one tuple of rot[xyzw] per point.
> I suppose the lag to be able to threat it as a vector it needs to process
> every tuple separately, I mean it needs to detect every tuple of channels.
> In the scope for th Lag CHOP I have put rot[xyzw]* to affect only rotations
> chennels.
> Looking at the help seems Lag Magnitude is designed to work with regular 3
> dimensional vectors, not sure if it designed to work with quaternions.
> In the case Lag is designed to work with 3 dimensional vectors and then it
> expects something like r[xyz]*. Then I have to split my quaternions in
> rotation axis and rotation angle and apply a Magnitude Lag to the r[xyz]*
> channels and the same lag but changing the mode to Lag Value to my angle*
> channels (being angle* the cahnnels with the rotation angle).
> About the spherical interpolation zhang mentioned, not sure if it is what I
> need to make a lag on my quaternions rotations.
>
> >
> > -Edward
> >
> >
> > On 01/09/2011 11:57 AM, Pablo Giménez wrote:
> >
> >> Hi all.
> >> I am having some weird problems trying to apply some CHOPs to quaternion
> >> channels.
> >> I have a quaternion rot attribute (vector4).
> >> I read it using a Geometry CHOP as rot[xyzw] channels.
> >> Then I apply a Lag CHOP ( I have similar problems using Spring). Most of
> >> the
> >> rotations for my points works all right, except some of them, some
> points
> >> randomly at some frames just flip.
> >> Like if I werent using quaternions and you get the typical rotations
> >> flipping due to euler angles limitations.
> >> If I pass through the channels and import my rot attribute again without
> >> any
> >> effect it works, but as soon I apply a lag it gives me this random
> >> rotation
> >> flipping.
> >> If I change  the lag parameters then the flipping happens in other
> points
> >> at
> >> different frames.
> >> Really weird.
> >> Has anybody tried to lag rotations using chops?
> >> Thanks.
> >>
> >>
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>
>
> --
> Un saludo
> Best Regards
> Pablo Giménez
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