Hi!

I have one weird problem with moi exports (probably not MOI fault but main app where mesh is created (Solidworks) but happens to me often so i need to find solution)
Is there a way how to see where is surface (polygon normals) directed ?
I often get some parts of mesh after export to OBJ fliped inwards unless i use doouble sidded materials. Flipping in my 3D app (LightWave) is not good in this case since Vertex normal is changed then and shading is wrong at rendertime. So I'm trying to see how could i "flip" them in the MOI beofore Export ? Is there a way to see surfaces as single sided so i can notice which ones are flipped/backwards and flip them somehow in MOI ?

Thanks

Hi Lewis - the easiest way to avoid worrying about flipped normals is to just use a double sided render material like you mentioned. Or another way that works easily is if you form your object into a completely closed solid volume, that will have normals oriented towards the outside of the volume.

If you have a surface or set of joined surfaces that does not make a solid volume, it is ambiguous which side of it is considered the positive surface normal. There is not currently any tool in MoI set up to visualize which side is the positive side, mostly because there isn't really anything in MoI itself that is sensitive to that. I had assumed earlier that if a program was sensitive to it, that they would also include tools to flip it if needed but yes unfortuantely often times there are bugs with just simple flipping where they don't flip vertex normals as well. I would think you should report that as a bug and see if they will fix it, it should not be a difficult thing to flip vertex normals at the same time as flipping polygons.

Although there isn't a way to visualize in Moi which side is the positive normal side, there is a Flip command that you can use to flip an open surface to the opposite direction:
http://moi3d.com/3.0/docs/moi_command_reference10.htm#flip

So if you do know which ones need flipping use the Flip command on them.

The other thing which can help a lot is if you make sure to join surfaces that are adjacent to one another even if you can't get them into a closed solid. That's because joined surfaces will at least have a consistent normal direction across the whole structure and it will be easier to deal with larger chunks of surfaces that act as one rather than a whole bunch of totally separate individual surfaces.

In the future I do want to add an option for displaying one side only or probably drawing backfaces in a fixed color like red but currently there isn't anything for that, sorry.

- Michael

>>Although there isn't a way to visualize in Moi which side is the positive normal side

Not directly but....

This trick works only with single surface, not joined, so you need to copy a one single surface from your joined object. (if you have joined object)

Click command >CPlane< and move the crosshairs along the "edge" and see what happens and cancel command..... File attached....

Other command that use normal's is>Shell< but notice, again single surface.

First method is easy....

Thanks for ....

Thanks for answers guys. I'll check those options. I've not modeled the mesh and i'ts modeled as is i.e. no time for changes/fixes nor do i have contact to initial perosn who made it but i've noticed that in past several times on some meshes from Solidworks and ProE.

As for double sided materials well that works for most of cases BUT in this particular case when at renderign fliped normals need to be emissive (glowing light) then it's not renderign in Octane so i need to make way to flip it to positive direction to be able to make them emitt light.

cheers