For solving the upvector problem, I've found the best approach is to
construct the upvector by using the previous frame's orientation as
reference. You can then apply various fudges to prevent the y unit vector of
the orientation matrix going too low or negative, and hence avoid it from
flipping. So it's almost like applying rotational forces to the particle to
keep it the right way up.
This does mean that you'll need to write an event to control the orientation
of your particles on every frame, so it takes a bit more work.
-----Original Message-----
From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of
Bradley Gabe
Sent: 20 June 2006 21:44
To: XSI(at)Softimage.COM
Subject: Re: Flipping birds
I don't think there's an "easy" way to do this at present, so be prepared to
do a little scripting.
Here's how I've handled this in the past:
1- For each particle, plot a path. (Do this by selecting your particles and
running Animate>Plot>Curve). Each curve will have a point per frame.
2- Use a trajectory constraint per bird to each path. This will ensure their
position per frame matches from the particle animation, as opposed to path
percentage.
3- Use the direction and up vector from the trajectory. If this doesn't
work, you have plenty of options to visualize the trajectory from here in
case of emergency. You could duplicate all your trajectories, create lofts,
and animate surface constraints... for example.
Hope this helps
-Brad
> I'm doing a flock of birds using particles and instances. however, I
> get some birds that are flipping (upside down) because of certain
> particle rotations. How can I keep them all from flipping? Is there an
> easy way to do this?
>
>
>
> Thanks!
>
>
>
> Martin Belleau
> FX Director
> Skuad Studios
> T:(514)844.3990
> C:(514)799.3990
>
>
>
>
---
Unsubscribe? Mail Majordomo(at)Softimage.COM with the following text in body:
unsubscribe xsi
---
Unsubscribe? Mail Majordomo(at)Softimage.COM with the following text in body:
unsubscribe xsi
