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???????

[Anonymous]

Ohhh, I see what you mean, I get 3 circles per quarter of ellipse. That works well enough, thank you.

[Dwight]

"Well enough?"

You mean as well as a chalk line drawn on raw plywood with 1/8" medite bent over it would?

[Anonymous]

well enough = perfectly, couldn't be any better

[Anonymous]

Hello Steven,
Small world indeed !
I have a library part, I wish I knew who wrote it,
that calculates the length of the string needed to
draw an ellipse of any given A and B dimensions.
The author states that he/she wrote the object
to do field layouts of ellipses using string and
stakes. I think string is too stretchy and would
use a surveyor's tape or a very light metal chain.
Peter Devlin

[Anonymous]

Steven wrote:
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???????

This is typical misunderstanding that the builder will actually use center of the circle and radius to build it unless it is small radius. Segment it and dimension the segments. That's how it's done in real world.

[Anonymous]

Miki wrote:
This is typical misunderstanding that the builder will actually use center of the circle and radius to build it unless it is small radius. Segment it and dimension the segments. That's how it's done in real world.

This is exactly how I will be doing it, breaking it into segments and dimensioning the three different circle segments.

Thanks to all for your help.