[Sidefx-houdini-list] Quaternons and Lag CHOP
pablogipi at gmail.com
Thu Sep 1 14:00:19 EDT 2011
2011/9/1 Edward Lam <edward at sidefx.com>
> Have you tried changing the Method to "Lag Magnitude" ?
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
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.
> 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
>> 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
>> 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
>> effect it works, but as soon I apply a lag it gives me this random
>> If I change the lag parameters then the flipping happens in other points
>> different frames.
>> Really weird.
>> Has anybody tried to lag rotations using chops?
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