[Sidefx-houdini-list] clean transforms

Robert Kelly isstuff at gmail.com
Fri May 28 12:08:28 EDT 2010


3d artists need to pass a test to get a licence to non-uniform scale

On 28 May 2010 09:01, Jeff Wagner <jeff at sidefx.com> wrote:
> 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):
>
> 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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