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Rendering with Arnold in Houdini and Solaris using the HtoA plug-in.
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Houdini scene scale for rendering Maya animated assets in Houdini

Message 1 of 4
2623 Views, 3 Replies

Houdini scene scale for rendering Maya animated assets in Houdini

Hi everyone...

We have a bit of a mind fudge on this one with scene scale sensitive parameters.

We work in Maya for animating some 2 meters characters with hair sims that are done in Houdini. But also, the final rendering and set dressing scenes are in Houdini as well. Using Heightfields, vegetation scattering, noise driven Vex deformations, etc.

Like many of you, we use 10 cm per Unit scaling in Maya. Normally, Houdini artists would scale down to 0.1 the maya assets, do their sim work, and scale the result back up for rendering in Maya. Yup Houdini is 1 meter per unit.

But while doing the lookDev in Houdini and using Htoa, an artist noticed how much hard it was to control the SSS. Especially using random walk but also displacements. Even with a very low SSS radius like 0.00001 the SSS was not scaling down anymore still giving a larger result. It was not possible to get the SSS small enough for the classic behind the ears effect per example.

So he tried removing the 0.1 scaling parent NULL and then Arnold was working as usual like in Maya with simillar parameters he was used to and with enough precision to narrow down the look he was looking for. But the character was now 20 meters high in Houdini.

Does anyone have any insights on this to share?

So far, the only thing we can think of, is to scale the resulting environment and fxs x10 for rendering with a giant character that plays nicely in Arnold. Sounds weird I know.

I know there is a render unit / scene scaling factor parameter in Mtoa in Maya and I think that could be very helpfull for our case. But I dont find it in the render settings in Houdini.

Thanks everyone for any toughts you can share!


Message 2 of 4
in reply to: slylebeau

So my understanding is that Arnold is 1 unit = 1 unit whatever the dcc you use. In Maya it's 1 cm and in Houdini its 1 meter. So trying to achieve a skin look in a "Meters context", you really need very small parameters for dermal, epidermal and subdermal layers SSS radiuses to acheive a look since this would be in a millimeter fashion.. And this even if the asset was scaled down by a 10x factor.

Message 3 of 4
in reply to: slylebeau

Another thing....

I think it could work with scaling the env and fxs x10.... But I fear about floating point precision artifacts if the whole thing get's too big and too far away from the origin. 😞

Message 4 of 4
in reply to: slylebeau

Hello, have you found the options on how to scale scenes in houdini?

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