[Sidefx-houdini-list] clean transforms

Jeff Wagner jeff at sidefx.com
Fri May 28 13:40:56 EDT 2010


Absolutely!

I have answered this question a few times and already have a blog mostly 
done that covers Maya to Houdini constraints in all it's forms.


-jeff

Pablo Giménez wrote:
> 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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