# How to Draw Lines Tangent to an Ellipse

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I have an ellipse of specific dimensions which I need to segment with straight lines of specific lengths that are tangent to the ellipse. The lines are of different lengths. It is the line endpoints that are tangent.

Can anyone let me know how to do this?

Thanks,

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Possibly use "snap to tangent" in the Osnaps?

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Have been trying that but does not seem to work. If I start my line, put in the distance there is no osnap available. The line is done. The tangent osnap does not seem to be working even when I start the line and then click on the tangent osnap. I do not get the symbol for the tangent anywhere on the ellipse.

Have been trying to use the align command with endpoint and perpendicular, but not real accurate.

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Hmmm.. That seems odd - could you possibly post a sample of what you are trying to accomplish?

thanks

Lee

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This is the drawing I am working on. 6' door with 2' glass panels which follow the ellipse. 1/4" sealant joint between glass panels. 2' wide door jambs.

Thanks,

RWW LEASING OFFICE FP.dwg

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The endpoints of line segments cannot be tangent at both ends, same is true for any curved objects. Midpoints could be tangent though.

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Well, that clears up alot of it. Thanks for the reply. Was hoping there was an easy way to do this in AutoCAD.

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By definition, if a line is tangential to a curve, it makes contact at only one point. You cannot create a line that is tangent to a closed curve (circle or ellipse) on both ends.

If you are looking to create chords (line segments formed from two points on a circle) I would recommend creating a line from the centr of the ellipse through the quadrant at the minor axis. Then use a polar ARRAY to create many copies of the line based on the angle between them. In the example I made in your drawing I used an angle to fill of 360 and an angle between items of 18 degrees. I then drew a polyline connecting all of the intersecting points (shown green). and offset this an arbitray distance to each side (shown blue). Really this is more of a geometry question than one of CAD. I hope this clears it up for you though.

RWW Example.dwg

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The only way that I have been able to do that is to create my ellipse, draw a couple of "crossing lines", trim the elipse, then draw the line that I want to reach the tangent.

If I need a full ellipse after drawing in the line-to-tangent, I will just re-draw the ellipse into place.

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Can't actually see the drawings as they are not in 2000 format, but by the sound of it - just thought you may need this:

:D:D:D:D:D:D:D:D

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Thanks, I need every bit of help I can get.

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You can draw line segments tangent to an ellipse, you just need to start the line segment outside the ellipse, then use the "tan" osnap. To get the line to be a particular length, use the "lengthen" command. (Just throwing that out there, not sure what your constraints are).

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I think you are misnaming the line you want to draw. I think it should be a chord of 2ft. The way to set these out is to draw a series of circles of radius 2ft and where the circle intersects the ellipse is your next circle centre point.

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I'm with eldon here

sometimes it's the old drawing board methods that work best

technically an elipse has two centres, so trying to use the dead centre of one to carry out geometrical gymnastics is likely to produce skewed results

I've tried working with elipses before and remember them refusing to respond to some of the snaps and having to resort to a long hand method (perhaps using 'perpendicular' instead of tangent)

Start your circles with the first centre on the 12 o'clock point, making the centre of the next where the intersection of the first and the elipse is, and the radius equal to the length of line you need

if you need a line and not a point at the 12 o'clock position, make the first circle diameter equal to the length you need, then following circles twice the size

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Thanks again for all the help. I will keep working on this. Thank God this does not come up very often, but interesting problem. Will try to get it right.

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Good Luck dSwinty

Let us know how it goes

Cheers

Lee

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• 1 year later...

Hey guys,

I have another question related with this subjects;

I need to draw a tangent line through an arbitrary point of an ellips. I need this because after that I will draw a normal to the tangent line in contact point. Without a tangent line I can't draw a normal in autocad. I know it is not directly related with cad drawing and very complex question. But I hope there is someone who tried it before and knows a practical approximate solution..

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First place the door, then trim from the left door jamb to the quadrant at 9 oclock so you are left with the upper left quadrant of the ellipse. Now use the divide command for however many segments you want, draw between the nodes, go from there. Depending on what you are trying to do you may want to use a complete quadrant, divide, then fit in the door and use a spacer from the window to the door, etc.

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Hey guys,

I have another question related with this subjects;

I need to draw a tangent line through an arbitrary point of an ellips. I need this because after that I will draw a normal to the tangent line in contact point. Without a tangent line I can't draw a normal in autocad. I know it is not directly related with cad drawing and very complex question. But I hope there is someone who tried it before and knows a practical approximate solution..

Always start another thread otherwise your question will get lost in the static.

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• 9 years later...

Hi there.

There is no regular way to draw a tangential line to an ellipse at a specific point on ellipse. But if you want to draw a line on an uncertain point, you may do it by use of "OSNAP".

In fact, you must employ the geometry rules and then apply it on drawing. There is a simple way to manually draw a tangential line to an ellipse at a specific point that you can find it on the internet.

Otherwise, I suggest you to learn parametric drawing which is very easy to learn. you just have to learn how restrictions works on drawing object and then you'll be able to do everything  you want.

1343774@gmail.com

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