Re: "link with" expressions in rigging - good or not?

[Adam Sale <adamsale(at)shaw.ca>]

hey bernard.. this is a problem I've noted and reported a few times since v5 I believe.

it sees to happen only when linking shape weights to other controls.. setting relative values seems to only log a single value change for the curve for whatever reason. The key is there, but at the wrong value, so I always end up going in an fixing by hand or scripted solution. I thought for a while it was only myself having this issue, but I did get support to repro the problem about a year or two ago. Can't remember who its was though?

 

this problem doesn't happen to me on linking transforms..

 

other than that one annoyance, as Brad wrote, I use them all the time, and I'm never left out to dry...

 

Adam
----- Original Message -----
From: Bradley Gabe <withanar@gmail.com>
Date: Tuesday, September 25, 2007 2:00 pm
Subject: Re: "link with" expressions in rigging - good or not?
To: XSI@Softimage.COM

> Hi Bernard. "Link with" operations are entirely stable and
> reliable, and I
> have used them many times in many productions without incident.
>
> The thing that is potentially unstable are the local Euler
> results you get
> from a pose or orientation constraint. Constraints are applied
> at the global
> level and use quaternion math for the calculations. As the
> results are
> calculated and applied back to the local rotations, they may
> shift between
> quadrants. When you have a local rotation that relies on a
> consistent range
> of values, say between -180 and 180, this can destroy the
> relationship you
> thought you were getting, since local 360 is as good as 0 to the
> globalvalue. This applies to normal expressions as well as "link
> with" operations.
>
> The solution is, any nodes you are using for expressions or
> "link with" ops,
> make sure to set animation keyframes on the local rotation at
> 0,0,0. This
> will force the global constraints to always resolve in the same local
> quadrant, and thus you can rely on your relationships always
> performingproperly.
>
> FYI, I have notified Softimage about this issue many times. I
> have logged it
> as a bug and also via escalation. I don't know if it has a UDEV
> number or is
> being tracked. It may be one of those issues that's too deep to easily
> solve, and there is a known workaround, so it's low priority.
>
> -Brad
>
>
>
> On 9/25/07, Bernard Lebel <3dbernard@gmail.com> wrote:
> >
> > Hello,
> >
> > Not really a support question, but rather getting a feel people's
> > experience in general compared to my own.
> >
> >
> > We have a bunch of characters, that I have not rigged.
> > The modeler created some shapes.
> > The rigger created a cpset to control the shape weights, with nice
> > sliders.
> > The thing is that the relationship between the shape weights
> in the
> > mixer and the cpset parameters are not (=) expressions, but "link
> > with" expressions.
> >
> > Now, the problem we're continually having is that somehow the
> > relationship between the shape weights and the sliders break. It
> > doesn't look like it's broken (I've checked 100 times, every element
> > of the expressions is there and valid), but moving the sliders
> has no
> > effect anymore on the shape weights.
> >
> > In time I have written lengthy scripts to workaround this problem.
> > It's ugly but it works. However, even though it's no longer a
> > show-stopper, animators are keep reporting that they have to
> use my
> > scripts to repair the shapes. The typical case happens when the
> > animator exports the mixer and imports it back onto the model.
> >
> > We're not using reference models.
> >
> > Perhaps there is something wrong we did in the first place, I don't
> > know. I don't know all the details of the rig (it's extremely
> > elaborate). However nothing seems non-legit to me.
> >
> > Obviously, my faith in "link with" _expression_ has taken quite
> a toll
> > as a result. I could have fired this to support but we're not on
> > maintenance.
> >
> >
> >
> > So my question is this: how much use of "link with"
> expressions do you
> > make in rigging? Is my experience unique? What are the things
> to do
> > and not do when using those?
> >
> >
> >
> > Thanks!
> > Bernard
> > ---
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