[Sidefx-houdini-list] clean transforms

Pablo Giménez pablogipi at gmail.com
Fri May 28 13:19:02 EDT 2010


2010/5/28 Jeff Wagner <jeff at sidefx.com>

> I use pre-transforms quite often but in rigs only.
>
> I would not recommend that you channel reference any Transform channels
> on an object in a character hierarchy. Use Rivet Object or hscript
> expression functions (known as constraints in other apps):
>
Probably Off-Topic, but would eb great Jeff  to have an entry in the Old
School blog about  different ways to mimic constraints from other packages
in Houdini.
For me the best way is using chops and the in particualr the Object CHOP,
whixh grabs the real transform from an object an then apply it another
object.
 Blend OBJ is also useful but the problem with it is that it applyes all the
transform realted to the parent(s) of the blend object, and not in the space
of the target object.
I mean is like setting the pivopt of the transform in the BlenOBJ rather
than in the object that receive the transform, MAya for instance usually
works in this way.


> vtorigin()[0], vtorigin[1], vtorigin()[2] to grab x, y and z translates
> vrorigin()...
> origin()...
>
> These will return the real world position relative to any other object
> in the network regardless of pre-transforms.
>
> One reason why pre-transforms exist is that in heavy rigs with thousands
> of nodes, using nulls just to locate other objects does indeed have a
> memory overhead (something like 15k...) so using pre-tranforms reduces
> the memory footprint and efficiency to a degree.
>
> Pre-transforms don't make much sense outside of char and prop rigs as
> Alex mentioned.
>
>
> One issue in all of this is if you somehow introduce non-proportional
> scales buried in a pre-transform. That really can screw you up something
> good in any rig in any software. I have a tool where I select two
> objects and it returns the transforms to get from one to the other. It
> flags any objects that have a non-prop scale in the pre-transform or the
> scale parms.
>
>
> -jeff
>
> Alex Lim wrote:
> > Hi,
> >
> > Other people might have a different opinion on this, but IMHO, yes and
> no.
> >
> > Yes, I think you may get into trouble if you zero'd an Object out
> > somewhere in the world space, but then later you perform additional
> > transform operation there, you may not notice (initially) that there are
> > cleaned transform in that node. So if you or someone else do a lot of
> > referencing to that Object chain, there is a little danger that when
> > your hierarchy get complicated, you will be spending a lot of time
> > figuring out why the numbers don't match up just because you used some
> > expressions that may not take into account pre-transform.
> >
> > I rarely see pre-transform on FX and lighting setups. Mostly on rigging,
> > it seems. Which made sense because you'd probably want to give animators
> > a clean, zero'd parameter rig to work with.
> >
> >
> >
> >
> > No, pre-transform can still be extracted regardless, either by
> > combination of objpretransform() and explodematrix() or other expression
> > functions. It is a useful thing.
> >
> >
> > IMHO, you should be able to work without cleaning transform in Houdini
> > tho. But if you have to, just make sure things are well labeled/noted
> > and you should be okay. :)
> >
> >
> > HTH,
> > Alex
> >
> >
> >
> >
> > On 5/28/2010 8:00 AM, James Rutherford wrote:
> >
> >> Probably a dumb question but will get into a future problem if I clean
> transforms on chain root nulls on a rig I'm working on.
> >> Jim Rutherford
> >>
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-- 
Un saludo
Best Regards
Pablo Giménez



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