Making an Ellipse from three points

Hello,

I'm just starting to use grasshopper and I have a quick question about making ellipses. From the version I have of grasshopper now, and I think it's the most updated, I can make ellipses through either base plane+2radii or I can make one inscribed in a triangle defined by three points.

I was wondering if grasshopper offered like...other functions that you could download? Because if so, I was wondering if there's an ellipse function available that makes ellipses based off three points, like the 3-point arc function that you can use. It would just make life easier with the code I have, that's all. Maybe this is available in an add-on?

Thanks

Replies to This Discussion

Permalink Reply by djordje on November 13, 2014 at 6:33pm

Hi Michael,

Take a look at this topic.

Permalink Reply by David Rutten on November 14, 2014 at 2:20am

Three points do not define a unique ellipse, at least not in the same way as arcs or circles. If you want to define an ellipse by spe ifying points on it, you'll need four points, no three of which are colinear and no two of which are coincident.

Permalink Reply by Fabrizio De Paolis on May 26, 2017 at 10:18am

Same problem here. I keep getting error trying to make ellipse from foci.

Can anyone help me please?

Thanks

Attachments:

revolution.gh, 16 KB

Permalink Reply by Birk Binnard on May 26, 2017 at 4:02pm

2 foci allow an infinite number of elipses to be created. Perhaps this physical exercise will help you figure out how to use GH to make ellipses using 2 foci:

1.Put 2 nails in a board a distance apart equal to the length of your hand (more or less)

2. Make a loop from a piece of string 3 times this length (more or less). Put the loop over the 2 nails.

3. Hold a pencil vertically inside the loop and push it out as far as as the string will let it go.

4. Move the pencil around on the board, always keeping tight tension between the pencil and the string. The resulting image the pencil draws is an ellipse.

Note that at any time during the drawing of the ellipse the string forms a triangle shape. The sum of the length is the triangle's 3 sides is the length of the string used to make the loop. On of these lengths is, of course, the distance between the nails/foci.

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