Hello Michael and everyone,

I tried to search for discussion related to this issue but to no avail.

I was struggling with these artifacts showing up on transparent object in modo601/MODO801 which is originally exported from MoI V3.
It seems OK as long as it's opaque. (Thanks to smart meshing system in MoI. )
But once I'd assigned transparent material and set refractive index to other than 1.0(1.434 flourite) to make it look photorealistic,
these wavy artifacts sometimes became noticeable.

I did some tests to figure out what caused these problems.
Finally I've managed to get rid of them by unticking "LWO options/Scale output units to meters" and scaling it in item mode in modo to sit at the same position as it was in MoI.
(I set both units to millimeters. So I have to scale MoI object in modo.)

Even though most of the time the artifact could not be seen from different camera angle, shape or lighting set etc., I'm happy to share this solution with someone here having a hard time dealing with it.

And I would really appreciate it if Michael or someone here would take a look at this to see if this LWO option has internal problems.

Thanks in advance,

Hisashi

(I love MoI from Japan)

Hi Hisashi, so the "Scale output units to meters" option only controls scaling of objects and does not change anything about materials. But it's a scaling that is applied directly to vertices not to an object's transform so I guess it is similar to doing the scale while in vertex mode in Modo.

The moire artifacts you are showing there look like a type of either z-fighting or self shadowing artifact. These types of render artifacts can be caused by raytracing where when the ray is fired out the start of the ray is too close to the surface and it ends up hitting the same surface it originated from, or also if there is a duplicate surface or other surface very close by. There is usually a "bias" factor option that can be edited to avoid this.

Most likely when you do the scaling in Item mode, the bias factor is being scaled along with the object, that's why you see a difference when you have done the scaling separately.

You should be able to fix the problem with the MoI "Scale output units to Meters" if you also adjust that bias factor to be better suited to the size of the object, those particular types of render parameters like bias factors are sensitive to the numeric size of an object and may need to be adjusted if your objects are of some different size than what the default settings expected.

Hope that makes sense. I'm not all that closely familiar with Modo myself so I'm not sure exactly where you go to adjust the bias factor, you may want to post on the Luxology forum for help with that.

But I have just double checked the code to make certain that the "Scale output units to meters" option in MoI only controls a scale factor applied to vertex positions and that's all that it does, not any changes to materials. It's just that some types of rendering especially raytracing of shadows or transparent materials are sensitive to bias factors which are size dependent and may need to be adjusted for objects which have a different size than what the default values are set to work for.

It also may be easier to do your work in Modo at the scale that the default render settings are tuned for rather than one much larger or smaller.

- Michael

Hi Michael,

Thank you for quick reply and looking into this!

I did further research on this and some of discussions on The Foundry forum enlightened me. It turns out that this is caused by MODO and it seems to be one of the known issues that The Foundry is working on.
The problem is that the PIVOT of the MESH is automatically transformed immediately after MODO imported LWO from MoI. I'm not smart enough to explain why pivot position affects shading,
but all I have to do is to delete additional pivot transformation channel from item/channel list then the artifacts disappear (or cut MoI mesh and paste in new mesh layer works as well).

I believe MoI doesn't do any harm.
So I'm sorry to take your time, Michael.
I'm now very happy that I don't need to be afraid of modeling transparent objects in MoI since some of my modeling tasks is a lot easier in nurbs than subD.

Thanks,

Hisashi

Hi Hisashi, no problem - I'm glad that you found out what causes the difference and have a way to adjust it! I don't know either why the pivot location would influence shading. Hopefully they'll be able to tune that up in the future.

Thanks, - Michael