From:  Michael Gibson
150.10 In reply to 150.9 
> Is that normal?
> An internal revolve's axe of a close curve don't works?
> Maybe a stupid question...but I am perplex :)

Eventually I will automatically trim the profile curve in half at the axis so that this will work.

Without trimming the profile, such a revolve would create a bad surface. I'll try to illustrate why - here is an image of what such a revolve would look like, just revolved by 90 degrees:

You can see that at the top and bottom the surface is compressed to a point in the middle and then flips over itself. This type of a surface is a problem. For things to work well, you should only have surfaces collapsed to a point along an edge (such as with a sphere), not at a point interior to the surface.

You can also see that if you were to continue to revolve another 90 degrees (for 180 total), it would be a closed surface, but it would not close cleanly since the surface's normals would be opposite at the spot where it was touching itself, and it would still have the collapsed point in the middle of it.

Then if you were to try to go by 360 degrees, it would cause it to be doubled over top of itself.

Does that make more sense seeing it in that small increment?

So to make a clean revolve your profile curve should be only to one side of the axis (until I do the automatic trimming). That will create a surface that is collapsed to a point only at its very edge and not right in the middle of the surface.

- Michael