# Where is elipse from centre tangent curve option?

Hi,
I see no command in elipse set for elipse tan to a curve drawn from centre let alone through a point for its one axis.
If circle has tan option icon why nothing in elipse ?

I tried osnap tan …no joy

then also Ctrl TanFrom but it doesnt see a snap occur when in my setp 3 I am at the curve.

my steps, using elipse from centre

1. click 0
2. click on 1
3. select via Ctrl Osnaps Tan option, and try to click on curve at 3

elipse centre point tan.3dm (32.7 KB)

Steve…

Correct, there is not a command- that must be at least partly because there is no ellipse that can fit these conditions, as far as I can see.

-Pascal

Hi,
I clicked on 0 then on 1 then dragged until elipse touched blue line, is that touch tangent ?

I was zoomed in well beyond 0.01 tolerance to judge touch.

Are you saying an elipse cant have a line tangent to it, forgetting my curve for a mo, and thinking of lines ?

Steve

I’m saying that an ellipse centered on your center point, & tangent to the line cannot pass through the perimeter point you’ve placed. I does come to ~.06 away in this case.

-Pascal

Hi Pascal,
I clicked on 0 then 1 so it passed through 1, then kissed the curve not with its other axis but the curve of the elipse.
Which is what I needed, some part of the elipse curve tan to blue curve.

see attached file

elipse centre point tan.3dm (46.6 KB)

Steve

You are correct, there must be a tangent ellipse - that is about the best way to find it that I can see.

-Pascal

What’s more important to you Steve:

1. That you make an ACTUAL textbook ellipse?
2. That it’s tangent to the blue line?
3. That it passes EXACTLY through point 1?

As Pascal pointed out, what you’re asking for is either not an actual ellipse (because what you’re looking for violates the definition of an ellipse for reasons which should be obvious). What are the priorities?

Well, there IS an ellipse that is tangent and hits the point, it is just not tangent on an axis.

-Pascal

Sure, you could use Scale1D to fix it up after you make the ellipse and make it hit, I was just trying to keep it a little more basic…

Hi,
I am after tangent on the elipse CURVE but not on its axis.

I am after a way to snap that curve to the blue curve.

Steve

Not the best solution, but here’s the closest I got without putting too much thought in it.

1. Your tangent point on the curve will be the closest point to the center of ellipse. So, just draw a perp from center to curve to find it. Discard existing point 3.
2. Since the angle between tangent points isn’t 90 deg. you need to find that third point of ellipse keeping in mind the ellipse curve passing through point 1.
3. Draw a perp from center in point 1 direction overshooting the point 1 for later trimmage (let’s call this curve “B”)
4. Draw a first (construction) ellipse clicking center, perp point on curve and point 3. It’s not gonna pass through point 1.
5. The next thing I did was - offset my ellipse with Through option to make the new offset’ed ellipse pass through point 1.
6. Trim curve “B” to the new ellipse and delete it.
7. Draw a second (construction) ellipse clicking center, perp point on curve and curve “B” trimmed end. It’s not gonna pass through point 1 again, but will already be within the document tolerance.
8. Offset new ellipse with Through option to make the new offset’ed ellipse pass through point 1 again.
9. Trim curve “B” to the new ellipse and delete it again.
10. Draw a third and final ellipse clicking center, perp point on curve and curve “B” trimmed end. It will pass through point 1 and will be far above document tolerance precision.

elipse centre point tan.3dm (33.6 KB)

P.S. You need to get all your geometry coplanar using ProjectToCPlane or Move vertical commands before drawing anything. Your points and curve aren’t in the same plane as center cross, so when you’re trying to draw an ellipse you’re not clicking on center point, but on center cross intersection which makes your ellipse 3D. Rotate your view and see for yourself.