[Sidefx-houdini-list] units in houdini

Michael Goldfarb goldfarb at corefa.com
Fri Feb 2 12:35:55 EST 2007

save it for the blog Jeff...sheesh...


Jeff Wagner wrote:
> I would assume that a Houdini unit is whatever you want it to be and
> build your tools accordingly. Steven refers to the units that are
> critical to DOPs when he mentions that a unit = 1 metre. Yes it is in
> the Preferences and was added for DOPs but that's all. A nice guideline
> but certainly not gospel.
> A houdini unit is whatever you want it to be. 
> Nothing is guaranteed with universal units. Units are cheated all the
> time. Many times in many facilities modelling many props with all kinds
> of different modelling tools, I have observed modellers delivering
> props, characters and sets in vastly different scales/units on the same
> job. It's a fact of life. Drives some TD's nuts. Others take it in
> stride and build the support needed and move on. 
> Tweaking scales of props, sets and other parts of a scene is an on-going
> issue. Units are also changed if the scene is too large or too small so
> you can work with it. Steven also mentioned this.
> 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.
>>>I'm planning to create a library of effects all based on the same
>>>scale to be used in different shots (wispy snow, snowstorm, rain etc.
>>>I receive the camera and the geometry cache in worldspace from maya
>>>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?
>>>Sidefx-houdini-list mailing list
>>>Sidefx-houdini-list at sidefx.com
>>Sidefx-houdini-list mailing list
>>Sidefx-houdini-list at sidefx.com

Michael Goldfarb                            email: goldfarb at corefa.com
c.o.r.e. digital pictures                        http://www.coredp.com
"Unless you're an astronaut, secret agent, vampire hunter,
or all three, you're probably a sellout; screw you."
- Maddox 2003

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