Funny thing!

 From:  Michael Gibson
4775.4 In reply to 4775.3 
Hi Felix - so that really weird looking one is not just a display artifact - that's a bad object that has some problem in its trim curves.

It looks like your base object in this case is a self-intersecting object which folds back over top of itself in some areas, like here:

Objects that have pieces of themselves that fold back over top of themselves will not be able to be handled properly by the booleans - so it's really the input into the booleans in this case that is causing the problem.

The boolean is generating some kind of messed up edge structure when it attempts to figure out how to process the surface/surface intersection calculations in that area - basically when a surface collapses down and then sticks back through itself it no longer has a single consistent outside surface normal, the surface normal is chaotic and one little step away from one area it has a completely opposite normal - this plays havoc with intersection calculations.

> The other thing I don't understand is why there is such an appearing
> different degree of smoothness between the objects after a boolean operation
> (test1.png, left object was boolean union).

The mesh only works with the visible area of surfaces, so when you do a boolean the booleaned result will get meshed differently since with new trim curves on it the active area of the surface is different.

If the active area of the surface happens to just exactly divide down to pieces which are right at the angle tolerance then it will give a rougher appearance.

That particular part is just a display artifact and is something you should just ignore.

Since the display mesher is constantly generating new meshes every time you do any kind of editing, it's very important for it to work very quickly so that you don't spend extra time waiting every time you do a boolean or a fillet or any kind of edit. The tradeoff for not having extra interruptions on every editing operation is that in some particular cases it can give a somewhat rough display.

> For now, the only way to know for sure it's only a display artifact, we have
> to export and render I guess. It would be nice to be able to check this
> inside MOI.

You can just go through the steps of doing an export but then just look at the export mesh which MoI displays when it shows the Meshing options dialog, but then just cancel out and not actually write the file.

See this previous message for how to set up a shortcut key so that you don't have to enter in a filename and can just push 1 key to generate an export mesh and see it on screen:

- Michael