[Sidefx-houdini-list] units in houdini

Luca Zappala luca at cinesite.co.uk
Tue Feb 6 13:07:44 EST 2007

Hi Jeff,

Thank you for the detailed reply; I take this could definitely be part 
of the 4# blog ! :-)
I'll be dealing mostly with particles so I'll have to be careful here.
I'll run some tests later on to see if pop forces respond proportionally 
to the global scale. When designing a similar system in another well 
known package with begins with M, (guess which one),
I found out that not all forces responded well to global scale changes. 
Actually two forces were not bound to the relative size at all. In other 
words it became a rather laborious job to accomodate for all the 
different forces behaviours when scaling :)


Jeff Wagner wrote:
> You should design your effects tools in such a way that you have a
> single global scale parameter that properly scales the effect up and
> down keeping both the behaviour and any shader patterns and other
> scale-dependent parts properly aligned.
> It is doable but requires some management as you build your effects
> tools. If this is for general consumption, it is worth it.
> In shaders that use procedural patterns, you can control globally within
> the shader how to control the scale up and down. Helps to use "rest"
> attributes. Same with SOPs.
> Particle sims are trickier but you can with trial and error get the same
> behaviour as you scale the environment that the sim is in.
> DOPs isn't so easy. You pretty much have to scale things down then up
> again going in to DOPs. Then again I haven't tried to build scalable
> sims in DOPs yet. I would imagine that RBD sims would be easier to work
> around than Cloth, wires, etc.
> -jeff
> On Fri, 2007-02-02 at 06:10 -0800, steven ong wrote:
>> Hi Luca,
>> A general rule of thumb is 1 m/unit in Houdini. When you read in
>> geometry from Maya, they will be hundreds of units in Houdini because
>> Maya is using 1cm/unit.
>> Unless the scale is so big that you get into precision errors, no need
>> to rescale either way, just work with the geometry as it is.
>> Cheers!
>> steven
>>> Hello,
>>> I'm planning to create a library of effects all based on the same
>>> scene
>>> scale to be used in different shots (wispy snow, snowstorm, rain etc.
>>> etc.).
>>> I receive the camera and the geometry cache in worldspace from maya
>>> for
>>> collisions emitters etc. etc.
>>> Is there a rule of thumb on what units use in houdini?
>>> Also do you rescale the maya assets down to a more convenient houdini
>>> scale, or do you do the other way around?
>>> thanks
>>> Luca
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