Hi Milkywaif,


> When I display control points of a newly created circle primitive in MoI and Rhino, I see
> different results. I already read your posts about this and you are saying unlike Rhino MoI
> evaluates control points in a different way so that we can edit objects more smoothly.

Yeah, it's a frequent area of confusion in Rhino that when you try to edit the points of a circle it behaves strangely, it basically gets kinks formed in it. If you grab any of those points in Rhino and drag them around you'll see that happening.

To make that kind of point editing easier in MoI there is an automatic rebuild that happens behind the scenes. In MoI when you turn on control points you actually see the control points of the rebuilt version which will smoothly deform if you grab any of the points and move them around, rather than devolving into something with sharp corners in it.



> Now please look at my example screenshot below. The shape on right is a rotated elliptical
> closed curve and left one is a perfect circle created from draw curve/circles.
> It's obvious that right one is an ellipse, we can tell that just by looking at the shape. But let's just
> assume, we can't tell the difference just by looking. Then how do we know that it's a circle in MoI?

Well, first of all you can't be sure that the shape you see in Rhino there is a circle just by glancing at it either, you would have to measure each of those points and also look at the weights of each point as well. It's not really good to judge "circularity" just by control point arrangement alone.

I've attached an example file here, which is not a circle despite having control points arranged exactly the same as in your screenshot. A NURBS circle needs not only the control points arranged in a certain way but also the weight values to have particular values as well.



> But let's just assume, we can't tell the difference just by looking. Then how do we know that it's a circle in MoI?

Well, normally you'd know it because you just used the Circle command to draw it... But if you somehow forgot how you created it, like Burr writes above if you select a circle or an arc then the size area of the properties panel will read a "Radius" value (which you can change by clicking on that line of the properties panel) rather than a generic bounding box "X by Y" size.


> Is there a built-in command or a script which circularizes any closed curve?

No there's nothing specifically for that currently, probably your best bet would be to just draw a new circle.


I'm not really sure _why_ you would have this situation of having curves that you were worried about being circular or not, are you doing some kind of reverse engineering task where you're trying to rebuild things from scanned data or something similar to that?


- Michael