Hi Felix,

> Is it the same for sweeps, lofts, etc? I know, I'm a
> very curious guy and I figure that if some operations
> are more like math function and others are more of an
> iterative type, the result of these ops. may differ in relative
> quality.

Loft is something that's calculated directly, but Sweep does go through an iterative fitting process, in a way the sweep is kind of like an automated loft that cooks up a bunch of profiles starting with a small number and measuring how accurate the result is and adding more profiles until the generated shape hugs the rail curves to a small enough distance.

But the error of such iterative functions is checked, in MoI the refinement will continue until the result is accurate to within 0.001 units.


> For example, I notice the 1 rail sweep I used seem to
> proceed by strait line segment to approximate the curve
> part of the rail.

Well these iterative methods actually produce curve output, the curve just gets more control points in it as it gets more refined.

The only way you should be seeing straight line segments in your sweep is if your rail curve is actually made up of straight line segments instead of being a curved shape itself.

Can you please post an attachment with the 3DM model file of your sweep so I can take a look at it and see what you are referring to?


> <...> or would it preferable to use another operation if possible of course.

Well, which tool is best really depends on the situation a lot - it would help a lot if you would post the model file to give some more specific context to what you are describing.


> I use a join operation on all the surfaces of my shape and
> MOI reports it's a joined surface and not a solid as I would
> have expected. Would it be better to use a Boolean union instead?

Well, that again depends on what particular problem you're running into - do you possibly have a surface missing leaving an open hole in the model? If so then for a situation like that you need to model a surface that fills in that hole and then join that in as well in order to make a fully closed skin. If you could post the 3DM model file that has your non-solid joined piece in it, that would help me to give you some more specific advice.

Boolean union (and the booleans in general) are more oriented towards intersecting objects with one another and removing some material from them. So for example if you have 2 cubes that are partially pushed through each other you would want to use boolean union which will intersect them and remove the area that is on the interior.

If you have a set of surfaces that all touch each other at common edges, where no material needs to be removed from anything then that's when Join is the right tool and not boolean union, although boolean union will often work the same for that, it will just try to do a lot of additional work to intersect things as well though.


> Another observation, the rails I used are made in 2 parts,
> a strait line and a some spline I would believe joined together.
> When I select the original rail it's all selected but when I try
> to select the edge of the sweep surface, Moi select only a single
> part at a time. This behavior makes me curious to understand
> what's going on.

Could you please post the model file so I could load it up and take a look at it?

If you have a rail curve that has sharp corners in it and is also not a planar shape, then that can cause the sweep to be made in individual sections along each smooth piece in between the sharp corners and you can end up with several disjoint objects from the sweep in that kind of a case.

If you have sharp corners in your rail and all the rail segments are on a single shared plane, then it will do corner mitering to make it all one piece.

But if you can post the model file that would help me to see what you're running into - it's really pretty hard for me to guess just by a written description because there are quite a lot of different things that can cause different results to be generated...

- Michael