Hi,

I'm trying to export some NURBS into OBJ format to get smooth groups for nice rendering in external 3D app but i get completely flipped (inside out polygons) for side that is mirrored in MOI.
Object is symmetrical so that's why i used mirror instead making both sides separatelly. I tried "Flip" command in MOI but there is no visual change in MOI (surfaces are always facing camera) and even if i ignore that and run the command to choose objects i want to flip after export there is no difference my mirrored side is still inside out in polygons at OBJ export :(.

Please help.

Thanks

Hi,
>> but there is no visual change in MOI
Old topic ?
http://moi3d.com/forum/index.php?webtag=MOI&msg=7578.3

Hi Lewis, the easiest way to get objects to have a consistent outward pointing normal in polygon output is to make your objects be closed solids and not just open surfaces. Solids will have their normals automatically oriented towards the outside of the volume.

For your object that won't generate a different export after the Flip command, maybe there's something about the particular object's structure that may be interfering with things like if it has a degenerate surface in it. I'd need to see your object to know more, you can post it here or e-mail it to me at moi@moi3d.com if you want to keep it confidential.

I just tested the MoI flip command over here on a simple case of a plane and it seems to be working as expected. Note that MoI itself always shows both sides of surfaces so that's normal that you won't see any visual change to the object in MoI after doing a Flip on it. But the export should be affected by it. If it isn't happening in your case maybe it's a bug or maybe it's a problem with the geometry, I'd need to see it to know more.

- Michael

Eddi, it's same problem but different case this time 'coz i made it in MOI directly (previously i was getting model from client) and Mirror tool in MOI made that problem now.

Michael - thanks, i sent you model to e-mail.

Hi Lewis, so Flip in MoI will only work on an entire object, you can't flip just some faces inside of a joined object. That's why you aren't getting any changes when doing the Flip. In NURBS modeling the orientation of a face is automatically determined by its topological connection to neighboring faces. Then it's possible to flip the whole structure.

Thanks for sending the object - it looks like there are a couple areas that have slight overlaps instead of being cleanly joined, and maybe there are some degenerate faces there. A degenerate face is a face that is squished down such that it has no surface area, it can potentially mess up topological face traversal.

I'll examine your object more closely to see if I can tune it up and send it back to you.

To see the potential problem areas, set up a shortcut key for highlighting naked edges as described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6051.2

- Michael

Michael, would be great to have correct normals and flipped normals displayed with different colors, for instance flipped normals can be always displayed blue, or even better to have a toggle function to enable and disable this feature.

Thanks for checking Michael,

As for slight overlaps i did notice on the nose/tip of mesh that there is 2 surfaces overlapping each other slightly although i have no idea how is that even possible 'coz what i did is i made plane in center of X axis and i Boolean everything and then deleted one half and then mirrored good half. So i should have exact join in the middle and nothing should be problematic, maybe mirror tool have some tolerance/decimal point error and made that small overlap somehow?

Is there maybe tool something like "Set Value" tool in LightWave where i could select all edges on half of split model and set them to 0.000 in X axis so that i'm sure that prior to mirroroing there is no surfaces that are "shorter" or "longer" so then mirroring must be perfect in the middle ?

Hi Lewis, I don't know why your mirror was off, I'd need to see the model right before the mirror to be able to tell you what happened there.

Some pieces seem to be off by just a very small amount around 0.002 units, which can be problematic since it's right around the join tolerance.

You can't edit the control points of edges like you can in LightWave - edges are markers that live on surfaces, it's the "underlying surface" that you can edit control points for.

I think I've located one spot that may be causing the most trouble, I'll e-mail more info to you after I've seen if I can repair it.

- Michael

Great, thanks again.

Is there way how i could edit mirror/join tolerance somewhere in options? I've searched but can't find any adjustable tolerance settings there. I think increasing tolerance on mirror/merge might weld/join all those small gaps/overlaps i see here and potentially solve it all much easier than trying to sort small errors around open/naked edges.

Hi Lewis, there isn't any setting for modifying the join tolerance, it scales automatically depending on the size of your objects. But at "regular object size" like you've got here the join tolerance will be 0.005 units - any edges within that distance of each other will get joined. If you scale your object down by 1/10 it will still be at "regular object size" but with a smaller gap between edges, that's effectively the same as increasing join tolerance.

So one process you can try to force edges to join with a looser tolerance is to scale your object down by 1/10 or 1/100 in size then rejoin it by using Edit > Separate on it followed by Edit > Join and then scale back up again. To scale something quickly by 1/10 select it and run Transform > Scale. At the first prompt to pick the scale origin type 0 and push enter to specify 0,0,0 as the scale origin, then at the next prompt where it asks for a scale factor type 0.1 and push enter. To scale back up after the rejoin repeat that but use 10.0 as the scale factor.

I just sent you an e-mail showing the location of what I think is causing the most problems, it's a spot with a tiny edge in it that is making an improperly formed trimming boundary for the surrounding faces. I sent you a file where I've rebuilt the faces around that spot and it should now behave properly for you I think.

- Michael

Thanks Michael, i'll try scale trick to force better tolerance merging.