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Constructing a 3-point ellipse....

Anonymous
Not applicable
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???????
15 REPLIES 15
Thomas Holm
Booster
Try Google. This is the first link I get:
http://www.uwgb.edu/DutchS/MATHALGO/Ellipses.HTM
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1
Anonymous
Not applicable
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
Not applicable
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
Not applicable
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
Not applicable
Ok, I'll take a look.

Small world Peter, I'm just across the river from you in Norwich...
Dwight
Newcomer
Draw your ellipse. Magic Wand it with the circle tool and you get your radii.
Dwight Atkinson
Anonymous
Not applicable
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
Newcomer
Magic wand the ellipse edge with "best match" selected and see what happens.
Dwight Atkinson
Anonymous
Not applicable
Dwight wrote:
Magic wand the ellipse edge with "best match" selected and see what happens.
What is "best match?"

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