Hi PaQ,

> Shading artefact :P there is no reflection on this one, so
> the line here are coming from Octane trying to smooth
> the whole stuff.

Well a box is a nice simple case to work with, so that's actually good...

Getting artifacts with welding turned on like this probably means that the faces in Octane are using a shared vertex normal even though in the OBJ file each of those faces only shares a 3D point location and has separate non-shared vertex normals.

Is it possible to recreate this problem with an export created from scratch in Modo?

Try making a simple 6-faced cube in Modo, make sure you have it welded so there are only 8 vertices for the cube (so like if you moved just one corner vertex all the faces move and not just one face like it would with stacked up individual vertices), then export that to an OBJ file.

Does the one exported from Modo also have the same artifact when read into Octane? Maybe post the Modo-generated OBJ cube here so I can look at it and verify that Modo wrote a welded OBJ file and did not do something like unweld it at export time only.


> That was the first trick we used ... but of course turning
> welding off introduce a lot of other problems, like discontinuity
> on every smooth surfaces.

Well, it would only have that kind of an effect with creating discontinuities on smooth surfaces if it is creating vertex normals itself rather than using the ones from the file.

If the vertex normals from the file were actually being used, turning welding off would have no effect on shading at all.

But when normals are created by an "averaging adjacent face normals" method, that's when welding can have an impact because non-welded polygons will not be considered to be adjacent...


So it really really looks like the vertex normals in the OBJ file are not being used...


Phil, is there any way to turn on a debug display to visualize the vertex normals within the Octane display?

That would probably help a lot if that could be set up, that way it would be a lot easier to point to one specific vertex normal and say "Look at that one, it is not right, it should be pointing like this instead" ...


> My main problem here is to explain it to Radiance, as he
> doesn't seems to understand the problem. From his pov,
> there is something special in MoI, whatever I can show.

Well, it should be possible to show him the same problem from other programs as well, since other CAD programs will produce similar structured things with vertex normals set up as well.

But maybe an easy first step would be to see if you can repeat the welded cube artifact problem from something created only in Modo.

- Michael