Another question:

How can I flip the surface normal in MoI? I haven't found this neither in the manual nor when searching the forum.

I get Rhino-Objects from someone else, convert them to polygons (obj) with MoI and then render them in XSI. But every now and then, the surface normals are inverted. Since I need to use the imported normals from MoI to get renderings without seams in XSI, I can not simply flip the polys in XSI.

Thank you!

Thomas Helzle

Hi Tommy, there currently isn't any way within MoI to flip the normals, there just isn't hardly anything within MoI itself right now that is sensitive to it.

If you can make a finished solid out of your object instead of an open surface, the normals should get oriented towards the "outside" automatically.

I really expected a polygon modeler to be able to handle flipping a mesh object correctly though. Instead of throwing out the vertex normals, XSI should just flip the normals as well as flipping the polygons. Is there any way you can submit a bug report to get this fixed up in XSI?

I do want to add a way to control flipping at export time from MoI in a future version though.

Until then it may be possible to use double-sided materials or something for these objects?

- Michael

Hi Michael,

no, XSI does it correctly IMO.

Since I need to use the "user defined normals" from MoI in XSI, it uses those very strictly.
Normal normals can be flipped easily in XSI, but not user normals AFAIK - which makes kind of sense.

There is a plugin to edit user normals for XSI, which includes the inversion of the normal direction, but it is rather old and I couldn't get it to work on the already existing normals from MOI. (Anybody knows how to make that possible? The docs are no longer available for that tool in Netview)

For normal objects this wouldn't be much of a problem - as you said it would be possible to just use doublesided materials. But in this case I am doing glass/water renderings for bottle-designs and the surface normal has to point in the right direction for the Inside/Outside based glass refraction and reflection calculations to work correctly.

I will try closing the surface completely and see if that helps. That sounds like it could work (the bottles are open on the top where the cap covers them).

EDIT: Closing the bottles at the top worked! Thank you so much for the fast help!

EDIT2: I spoke too early. It seems that of 3 bottles in the scene, 2 are correct and one is wrong - and which one seems to be random...

I think this is a very important thing to have inside of MoI though - not only on export.

Thank you very much!

Thomas

Hi Tommy,

> no, XSI does it correctly IMO.

I thought the way it was doing it was causing a problem for you?

It is understandable that under a general edit operation such as moving a single point of the mesh around, that they would throw out the pre-calculated vertex normals for that since it is difficult to figure out how to re-orient them to adapt to the subtle change in shape.

However, for other operations that do not change the shape they should try to keep any custom vertex normals in place.

For example, moving or rotating the entire object - they should not discard precalculated normals in this case.

Flipping is the same kind of thing, flipping does not change the shape so it is easy to keep the precalculated normals in this case, just multiply them by -1 to flip their direction as well.

The problem is that XSI is treating flipping as a kind of "custom edit operation" when it is actually a "vertex normal preserving edit operation".

It would be great if they would fix this up in XSI - if they did you would not have run across a problem in this case.

I didn't really worry about flipping initially since I thought any advanced polygon modeler would be able to handle flipping without causing any problems since it is such a basic operation, but it turns out that is not the case. Actually Cinema4D has the same problem as well.


> EDIT2: I spoke too early. It seems that of 3 bottles in the scene, 2 are correct and
> one is wrong - and which one seems to be random...

Can you please send the model files to me at moi@moi3d.com, I'll take a look and see what's wrong.

My guess would be that the bottle didn't get quite fully sealed into a solid?

- Michael

Hi Michael,

I think this is a typical problem of perspective... ;-)
If I would ask Softimage to "fix" this, they would say something like: "How on earth can a 3D-Modelling Software have no way to flip surface normals" but this time targeted at MoI ;-)

User Normals are something I NEVER ever use in any other software, be it Lightwave, Cinema or XSI, with the latter being the most advanced. There is little need for this when you do normal polygon modelling. So from my (and propably Softimages) view, this is something rare and special.
I don't know how user normals are treated when you edit or deform the model, but this is a massive challenge to do right IMO as well.

So I guess it is me writing a script for XSI to invert the imported user normals for now.

But since this is a typical problem, especially when importing IGES files where normals are often completely wrong, a way to view and flip Normals in MoI is important.

Sorry, those bottles are under NDA, so I can't send them to you.
I "fixed" it by exporting them several times and grab the bottles with the correct normals from the different exports.

Cheers!

Thomas

Hi Tommy, I guess the difference is that MoI does not particularly have any operation within its own functioning that really depends on the normal direction right now.

However, XSI's rendering function does behave differently depending on the normal direction... So that makes a lot of sense for them to have a flip function as part of their toolbox. It would be nice if their flip function wouldn't discard this important model data though.


> There is little need for this when you do normal polygon modelling.

True, but it seems like rendering is a pretty big function of XSI as well... Isn't that what you are using it for in this case? For rendering CAD data having accurate vertex normals is a really significant thing.


> I don't know how user normals are treated when you edit or deform the
> model, but this is a massive challenge to do right IMO as well.

It is for a fully general edit like tweaking a single point. But for a full-object rigid body transformation like move, rotate, scale, mirror or flip, it is really easy.

At any rate, I do want to add the ability to flip inside MoI in the future it just won't be a part of version 1.0 .

- Michael

Michael, so far I found workable solutions and workarounds for all my problems with MoI thanks to your help, so all is well.
Your knowledge and help here on the forum are worth much more than some features, so please do as you see fit for your development.

Thank you so much!

Thomas

Hi Thomas, thanks! And I'm glad that you have been able to work around those problems.

It helps me a lot to hear about the problems here on the forum because that generally helps me figure out what to work on to make improvements, although sometimes it will take a little while before I can get it implemented.

So thanks very much for your feedback and for sharing your cool renderings too!

- Michael