topic Re: Constructing a 3-point ellipse.... in Installation & update

Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 18:03:59 GMT

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???????

Re: Constructing a 3-point ellipse....

Thomas Holm — Wed, 03 Sep 2008 18:10:25 GMT

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

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 18:18:37 GMT

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

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 18:20:17 GMT

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...

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 18:31:53 GMT

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

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 18:36:12 GMT

Ok, I'll take a look.

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

Re: Constructing a 3-point ellipse....

Dwight — Wed, 03 Sep 2008 18:54:13 GMT

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

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 19:02:45 GMT

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!

Re: Constructing a 3-point ellipse....

Dwight — Wed, 03 Sep 2008 19:04:42 GMT

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

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 19:09:33 GMT

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

What is "best match?"

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 19:12:49 GMT

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

Re: Constructing a 3-point ellipse....

Dwight — Wed, 03 Sep 2008 19:22:06 GMT

"Well enough?"

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

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 19:34:13 GMT

well enough = perfectly, couldn't be any better

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 19:41:05 GMT

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

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 19:45:59 GMT

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.

Re: Constructing a 3-point ellipse....

Anonymous — Wed, 03 Sep 2008 19:54:27 GMT

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.