Hi Burr,

> One of the questions was regarding "sweep1 picture". if you look at
> the profiles and how they stand up then look at the resulting sweep,
> you'll see the smaller polygon rotated 45 degrees.

Actually that is also caused by the auto-place mechanism getting used. The auto-place can be kind of arbitrary about which direction it decides is the "up" direction when it automatically moves things into place, I think right now it may not quite work as expected if your profiles are drawn in a different view than the Top view.

If you move your shapes up to get auto-place turned off, you should also see that strange rotation disappear at same time as well.

There definitely does need to be some work to make auto-place have a more expected "up" direction when it kicks in, but probably your best bet for now would be to move those profiles up so that mode is not kicking in at all for this thing.


> I think I read in another thread there is a selection during sweep
> that is called "twist" that is doing this.

There is a twist parameter, but it is for controlling the behavior for how paths that move around fully in 3d up and down like a roller-coaster will behave, it won't actually control anything for your flat path like in this case.

- Michael

>The auto-place can be kind of arbitrary about which direction it decides is the "up" direction when it automatically moves things into place, I think right now it may not quite work as expected if your profiles are drawn in a different view than the Top view.

Just a thought, not that you dont have enough work, for your 2d objects like circles and squares and such, maybe some kind of "definition" about its rotation. I work in a cad program that does this with a 360 degree start/end point so your circle would "actually have a top" (or start point). Can this equate in nurbs creation?

Just a thought to jot down. Thanks again,
Burr

Hi Burr, yup NURBS circles work in exactly that same way, they have a start and end point that touch each other.

I usually call that the "seam" of the closed curve.

If you extrude a circle into a cylinder, you'll see where the seam was, it will then become the closing seam of the cylinder surface which is closed in a similar way (start and end touching).

There is stuff in MoI that is built in to try and minimize the amount of work that you have to do for manually ensuring that the seam is in the correct place. Like for instance if you loft between 3 circles, MoI will automatically analyze them and re-configure their seam points to match nicely so that the loft does not severely torque or twist.

You can actually adjust those seam points while you are in the final stage of the loft command if you want to purposely introduce twist - before you finish Loft you'll see those points displayed inside the viewport and you can click and drag on one to reposition it.


But I'm not completely sure if that's what you are mentioning - a lot of programs also keep an extra kind of "local axis" for each object that defines a rotation for the object...


Actually in this particular case of the "up" being weird in the Sweep, it isn't really the up of the profiles that is messed up, it is the "up" that is coming from the rail curve - part of the process of sweeping involves making a set of "frames" (like an x/y/z tripod) at each point along the rail.

- Michael

Ok thanks. The up has to do with a sweep calc.. Your original reply was exactly what I was talking about.

So, If i grab my polygon tool, and choose my first point, is my second click the seam? I can rotate around the origin and set the seam where I want? and if so, the properties panel you would like would have this as a "definable property", Eh!

Thanks for your reply.

Hi Burr,

> So, If i grab my polygon tool, and choose my first point,
> is my second click the seam?

Yup, that is correct.


> I can rotate around the origin and set the seam where I want?

Yes.


> and if so, the properties panel you would like would
> have this as a "definable property", Eh!

Yes, I would like to have it in there eventually. But it is sort of a less commonly used thing, I'm going to first focus on some basic properties like color for example. This will probably be a while longer before some of the more advanced properties get added there.

- Michael