A simple question from a newbie

[didier13]

hi all,

i have a simple question regarding unit in ICE. What are the base unit system?
for examples:
- a mass of 1 is equal to 1 kg?
- a speed of 1 is 1 m/s ?

etc..

thanks for your responses
Didier

[Tekano]

Hi Didier,

Are you tlaking about ICE, Rigid Bodies or Syflex? they all have their own defaults, I think Syflex cares more about precise kg and scene units than the others but really Softimage units can be whatever units you want them to be. Start with a simple convention like 1 mass = 1 kg and 1 unit = 1 metre and take it from there. if your scene is tiny then you may need to go 1 unit = 10cm , make the units to be whatever is suitable for you to use.

[Leo]

Hi Didier,

Are you tlaking about ICE, Rigid Bodies or Syflex? they all have their own defaults, I think Syflex cares more about precise kg and scene units than the others but really Softimage units can be whatever units you want them to be. Start with a simple convention like 1 mass = 1 kg and 1 unit = 1 metre and take it from there. if your scene is tiny then you may need to go 1 unit = 10cm , make the units to be whatever is suitable for you to use.

This is only half true, as a lot of the shaders in XSI calculate with 1 meter being equal to 10 SI units. Therefore it is usually a good idea to keep it at that, since it will cause the least issues later on in the post-simulation part of the project.

[didier13]

thanks for your responses. I was speaking about ICE. If i've understood well, it's like a "relative unit system" and you have to established references if you want to work like a real base physic system?
have you already compare this "1 to 10 ratio" to a "real" simple physic law?

thanks
Didier

[Tekano]

I'm really not sure which shaders Leo mentioned, perhaps the SSS or Physical sky shaders.... but yes its relative ratios, we do not do many commercials with 'live action' where I work, but this one it was a mix between Stop Motion, Live Action and CG and so for once we actually had live footage to work to as reference. I found that both ICE & syflex matched perfectly once the camera was tracked correctly and the gravity / scene scales were set up correctly to the shot. So I would not worry if I were you didier13, its all relative anyways - you may have to take into account air friction and object densities etc so its an imprecise science and I won't tell anyone if you have to use a gravity 0f 9.7 instead of 9.8 m/s ;)

http://www.youtube.com/user/STUDIOAKA#p ... NyhFLD3fsU
heres the commercial anyways- the confetti is ICE and the paper rings are Syflex. oh and the jack in the box spring is ICE too!

[Hirazi Blue]

The whole units dilemma can be confusing. The SI-devs have always maintained
(all the following quotes are from the 2012 User's Guide, the highlights are mine, obviously)

It is an arbitrary, relative value that can be anything you want

However, when working with Lagoa

When you emit Lagoa particles, the emitter object is the region in which the particle volume is initially contained and calculated. This region is divided up into Softimage units, and each unit is subdivided into cells. Each unit represents a fixed space of 10 cm and cannot be changed.

When working with Syflex

The Syflex ICE compounds and nodes are tuned so that 1 Softimage unit is equal to 10 cm

When working with Rigid Bodies

Both the PhysX and ODE dynamics engines have been tuned so that 1 Softimage unit is equal to 10 cm

So "1 Softimage unit equals 10 cm" seems a safe-enough bet (but you can vary it according to taste/necessity)
;)

[didier13]

I'm really not sure which shaders Leo mentioned, perhaps the SSS or Physical sky shaders.... but yes its relative ratios, we do not do many commercials with 'live action' where I work, but this one it was a mix between Stop Motion, Live Action and CG and so for once we actually had live footage to work to as reference. I found that both ICE & syflex matched perfectly once the camera was tracked correctly and the gravity / scene scales were set up correctly to the shot. So I would not worry if I were you didier13, its all relative anyways - you may have to take into account air friction and object densities etc so its an imprecise science and I won't tell anyone if you have to use a gravity 0f 9.7 instead of 9.8 m/s ;)

http://www.youtube.com/user/STUDIOAKA#p ... NyhFLD3fsU
heres the commercial anyways- the confetti is ICE and the paper rings are Syflex. oh and the jack in the box spring is ICE too!

Thanks Tekano,
you're right. Working in a relative ratios must match most of the needs in cg... i've just to take an habit to work this way ( For sure, 9.7 m/s instead of 9.8 m/s doesn't matter very much ;) )

[didier13]

The whole units dilemma can be confusing. The SI-devs have always maintained
(all the following quotes are from the 2012 User's Guide, the highlights are mine, obviously)

It is an arbitrary, relative value that can be anything you want

However, when working with Lagoa

When you emit Lagoa particles, the emitter object is the region in which the particle volume is initially contained and calculated. This region is divided up into Softimage units, and each unit is subdivided into cells. Each unit represents a fixed space of 10 cm and cannot be changed.

When working with Syflex

The Syflex ICE compounds and nodes are tuned so that 1 Softimage unit is equal to 10 cm

When working with Rigid Bodies

Both the PhysX and ODE dynamics engines have been tuned so that 1 Softimage unit is equal to 10 cm

So "1 Softimage unit equals 10 cm" seems a safe-enough bet (but you can vary it according to taste/necessity)
;)

Thanks for theses references, Hirazi Blue. It's good to hear that you have think about this relative unit sytem. I'll take care of this now.