Constructing a 3-point ellipse....

[Anonymous]

Hello,

I have no problem drawing an ellipse with the circle tool, but I need to dimension it so the builder can actually build it as drawn. I understand an ellipse is really 3 circles. What I need to do is find the foci of the 3 circles so I can dimension them properly.

Been a long time since high school geometry (I never really listened anyway, when would I even use it?? ha ha). Does anyone have a good method???????

[Thomas Holm]

Try Google. This is the first link I get:
http://www.uwgb.edu/DutchS/MATHALGO/Ellipses.HTM

[Anonymous]

Have you tried to dimension one this way? What the heck is OA? where do you draw the line for OA? is it arbitrary?

[Anonymous]

I did a google search before I posted but came up with unhelpful information like this one. Much different searching than actually trying to do it per their method...

[Anonymous]

An ellipse is NOT three circles but an approximation of an ellipse
can be drawn using either the "three center method" or
the "five center method" which use circular arc segments.
If you have "Architectural Graphic Standards", these two
approximations are explained. A true ellipse can be constructed
by various means also explained in "Architectural Graphic Standards".
Peter Devlin

[Anonymous]

Ok, I'll take a look.

Small world Peter, I'm just across the river from you in Norwich...

[Dwight]

Draw your ellipse. Magic Wand it with the circle tool and you get your radii.

[Anonymous]

Works pretty well, it gives you the two circles that make the ellipse... but then the two circles don't connect. Anyway, you've got me the closest so far!

[Dwight]

Magic wand the ellipse edge with "best match" selected and see what happens.

[Anonymous]

Dwight wrote:
Magic wand the ellipse edge with "best match" selected and see what happens.

What is "best match?"