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PeterW 04-28-2008 01:28 PM

Dome Calculator
I was hunting the web for some dome info and found this website Dome Calculators

Its got some useful bits for those that want to work out the finer points of their designs ! It does a lot of the math for you without the effort. What is good is the 'Level' field, which gives you the dome radius at whatever interval you request.

It is unit independent, so you can put your calcs in as millimetres, inches, cables or whatever you desire. :D



dmun 04-28-2008 01:44 PM

Re: Dome Calculator
That's a good find. I once tried to find a way to locate the focii of an ellipse, to lay out a flower garden, and lacking a tool like this, I had to estimate by trial and error.

gjbingham 04-28-2008 06:07 PM

Re: Dome Calculator
There's a formula for the foci of an eclipse somewhere. I think I did that in physics a hundred years ago. I found this here:

Foci of an ellipse - Math Open Reference

An ellipse is defined in part by the location of the foci. However if you have an ellipse with known major and minor axis lengths, you can find the location of the foci using the formula below where
F is the distance from each focus to the center (see figure above)
j is the semi-major axis (major radius)
n is the semi-minor axis (minor radius)

In the figure above, drag any of the four orange dots. This will change the length of the major and minor axes. You will see how the foci move and the calculation will change to reflect their new location.

Almost completely useless information in everyday life, unless your doing a project like yours.

asudavew 04-28-2008 06:11 PM

Re: Dome Calculator
There you guys go again....

confusing poor dave!

Ed_ 04-29-2008 07:16 AM

Re: Dome Calculator
At any point on an ellipse, the sum of the distances to the two foci will always be the same. You can exploit this to draw one pretty neatly--put stakes at the foci, and attach the two ends of a string to the stakes. The string should have just enough slack that, when pulled tight, the point you're pulling reaches the edge. (i.e. longer string = bigger ellipse) Move the foci farther apart to make it longer and skinnier.

Then by pulling the string taut in different directions, you can find your outline. Just be careful not to get it wound around the stakes.

Of course, when the foci move to the same point, the ellipse becomes a circle.

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