title : Edges crease marks on .obj exports

Hello, is there any infos about how edge creases are marked on .obj exported models.

Is there an angle threshold at which edges are marked ? is there a workaround to export, trim, or select only theses hard edges in MoI ?

I just try to understand how to handle the exported polys. Maybe I'm missing something about NGons.

thx

Edit : forgot to title the thread. cant change it.

Hi delic I updated the title for you.

For MoI's .obj export edge creasing is handled by vertex normals that are stored in the .obj file, which control the shading of the polygons.

So there is no angle threshold set - usually an angle threshold mechanism is used when vertex normals are being created by averaging together face normals of adjacent polygon faces. With MoI's export the vertex normals instead come from the original NURBS surface. For an edge crease the polygons on either side of the crease will have their own distinct vertex normals.

This is again a big difference from a polygon modeling program - when you create geometry in MoI the stuff you create are actual smooth spine surfaces, which is rather different than polygon mesh geometry that's made up of all flat pieces. MoI's geometry will display whatever the actual geometry is defining, it will show smooth if the surfaces are actually smooth to each other, or display creased if there is an actual crease between the surfaces. It does not work like a polygon mesh environment where it's faking a smooth look between flat pieces that meet under some angle threshold.


> Is there an angle threshold at which edges are marked ? is there a workaround to
> export, trim, or select only theses hard edges in MoI ?

Sorry I don't quite understand this question - MoI can only export .obj data, not import it back in again so it's not able to select any of those polygon edges at all... Basically once you export to .obj files the data is transformed into a different type of 3D object, made up of flat polygon pieces rather than NURBS surfaces.


But basically if you want things to look smooth they have to be constructed to be actually smooth to each other, using tools like Fillet or Blend that construct surfaces which are continuous with their neighbors.

- Michael

Ok, thanks Michael, it's clear.

My question was about this case : I wonder why the edge mark stops before the end. Which does on the other end. But I guess it depends on how I generated these surface, two networks here, from two trimmed curves. At first I expected the mark would reach both end lines.
Joining these surfaces shouldn't change them, maybe it's the welding of obj exporter.

Hi delic - things like that happen because of localized refinement in the mesh, the way the mesher works is it starts with a somewhat rougher uniformly spaced mesh and then subdivides any areas of that rough mesh where normals are further apart than the angle tolerance that you pick. If the surface is curved in different amounts on either side of a sharp crease it's possible for some refinement to be added more on one side than the other and you'll see stuff like that.

So it's just sort of a normal side effect from how meshing works in general - being able to add localized density just to areas that are more highly curved allows the mesh to have more density just in more tightly curved areas. If there were no levels of shifts in subdivisions (which would then continue edge loops as you are looking for) it would become very difficult to capture small curved details in things with a uniformly divided mesh.

Overall MoI's mesher is more oriented around making a mesh that is going to render well with a lower polygon count, it's not focused on trying to make sub-d smoothing friendly topology and so it's not trying to do things like make long edge loops like you may be used to if you have been focused on doing sub-d modeling.

- Michael

Thanks a lot Michael, again the answer is very clear.

I must say that the exported meshes are really good for rendering.