Hi Anthony,

> i was saying that i'm trying to find a definition of an ellipse
> that works equally well in real life and moi.

Well, an ellipse is sort of a mathematical concept - you can't actually create an actual 100% exact one in real life, stuff like the paper you use is not 100% flat but has little tiny bumps in it, if you draw it with a pen it won't have 0 width like an actual true ellipse, etc, etc...

Do you mean a method to make a sketch representation of an ellipse in real life just using a pencil and paper?

Some kinds of pencil and paper sketch methods can translate well into MoI when they involve stuff like drawing some auxilary shapes and finding intersections between them for where to start new lines at and stuff like that.

But an ellipse is a continuously changing curve, it's a lot different than drawing a line - methods that involve some kind of continuous change applied to the pencil won't really have a very good direct equivalent in MoI. I guess you could try using the Sketch command to do a brush stroke type approximation, but it will be really difficult to get a high quality approximation without wiggles in it - meanwhile if you use the actual ellipse or conic drawing tools you get a super precise ellipse.

I guess if you were really intent on simulating a pencil or pen draw method you could write a script that basically drew a curve that was plotted with a whole lot of control points in it. If you've seen some of the function curve plotting commands that Brian has posted earlier, that's how those were made. But I really can't see how that would be of any benefit for the case of an ellipse though, since with NURBS an ellipse does not have to be approximated it can be formed exactly instead which is what the ellipse and conic commands do.


One of the sketch based ways for drawing an ellipse is to put 2 pins in at the foci points and then have a length of string between them, then if you hold the string taut with a pencil and drag it, it will trace a sketch of an ellipse. That's again though the kind of continuously changing pencil stroke type operation that doesn't really translate very well into MoI as a construction technique.

If you wanted to define an ellipse mathematically instead of by some kind of "pencil sketching with apparatus" method then that would translate more directly into MoI's ellipse or conic drawing commands though...

Again though, I'm still not entirely sure if I completely understand what you're looking for. Just in general in the more abstract environment of CAD systems you can't necessarily use drawing methods that involve some kinds of physical processes like tension or friction with various moving parts and apparatus or stuff like that... But on the other hand with CAD you are more free to make exact mathematically defined stuff more directly instead of trying to simulate them with physical processes....

- Michael