Elipse through points ..no command?

Hi,
just as there is circle through points, where is the command elipse through points ?

I want to best fit an elipse through points plotted on what is known to be the route of an elipse.

Steve

Not to hijack, but in the best spirit of piling on: What about circles, arcs and ellipses having the option to construct by center and a tangent? In the case of arcs they would also need a start and stop which could be any of the usual osnaps, and in the case of ellipses they would need a specification for orientation of the axes and the ratio of major to minor axis lengths.

i’m not really sure how many points would be needed to define a unique ellipse but with three points —

(as in, there are multiple solutions to EllipseThroughPoints so that’s probably why there’s no command for it)

Hi,
I realise that three points can have many solutions, but to have a command that requires a minimum of x number of points could be done. I have enough to allow an elipse but not an arc or circle.

To add further to my quest, attached a 3dm file showing the points. I can make out some parts of a weld forming the edge of what I know to be an eliptical tank, I show outer weld edge, and lines that form the limit of the elipse, also some for inner weld.

My best chance is to fit an elipse to the outer weld edge, but how ?

I have more of this nature in due course, so an easy way, without grasshopper and things that look like UFO language, is best for my sanity just now.
weld elipse.3dm (31.5 KB)
Steve

you can mostly do this stuff with Perp snap. could be more powerful though i suppose

see my post with my points, can perp snap do those ?

Steve

i’ll look at your file in a bit… for clarity, i was saying perp snap allows one to draw a circle/arc/ellipse using a center point and a tangent

It’s true that some type of additional definition would be required as I suggested for ellipses in my post above. It’s also possible to over-specify so there’s no solution. In the circle commands we already have available the McNeel folks have done a wonderful job of making the whole thing interactive so the designer can search around with the mouse to find the points required. I would think they could add the requested options fairly easily if they were sufficiently motivated. With McNeel’s globally dispersed developer team I think that would require dispatching a lot of beer trucks.

Boy, you guys type fast. My 2nd post was in reply to your first one, Jeff.

[quote=“Steve1, post:4, topic:30405, full:true”]
Hi,
I realise that three points can have many solutions, but to have a command that requires a minimum of x number of points could be done. I have enough to allow an elipse but not an arc or circle.[/quote]

according to this:

you need at least 5 points to define an ellipse… but the problem is, those five points don’t always mean an ellipse can be created through them.

i don’t think a true ellipse goes through any set of those points&lines…
maybe something like this will do which will keep the ellipse constrained to the boundaries you have drawn then using Ellipse: Corners, use eye to get the close fit.

I got a déjà-vu feeling on this one as soon as I read the first line…

Boy, it even has the same title :upside_down: :
http://discourse.mcneel.com/t/elipse-through-points-no-command/9843/1

And then there are these - all by Steve:
http://discourse.mcneel.com/t/establishing-major-axis-of-an-elipse-type-closed-curve-how/
http://discourse.mcneel.com/t/where-is-elipse-from-centre-tangent-curve-option/
http://discourse.mcneel.com/t/how-to-find-centre-of-an-elipse/

Feel like we are going in circles once in a while - errr… make that ellipses.

3 Likes

I do find myself working with elipses and each of these was a different puzzle but I see I could have solved it in some cases with elipse through points such as the need to put an elipse through points resulting from projecting circle onto curved surface.

There have to be occasions where it is going to be an elipse, it has enough points, the item traced is known to be an elipse etc etc or the result closely matches an elipse and I need to create an elipse from it.

image of the 3dm file attached.

With no easy command forthcoming I end up faced with the same problem each time.

situation 1.
project a circle onto a surface curving in one direction, surface a bit ripply, we get an elipse, turn curve into points and fit elipse to them.
situation 2, my case above.
situation 3. elipse tan to line, solved in that case by knowing the centre beforehand, so perp line centre to line.

attached a situation where the points ARE EXACTLY FITTING AN ELIPSE, use bounding box, fails, curvethroughPts fail.
Elipse will fit fails with boundingBox.3dm (55.0 KB)
still not sure what way is best to put elipse through points. Do all CAD progs fail at this apparent simple task when enough points exist to best fit an elipse ?

Steve

Well, clearly the points will not make the same bounding box as the ellipse that fits through them unless points happen to fall on the quads of the ellipse. Scale1D the initial ellipse from its center to match the points better.

Use PointDeviation if you want to get it to some tolerance.

BTW, CurveThroughPt makes a decent ellipsish thing if you set Knots=Chord. Use that curve to make the bounding box for the ellipse tool and it works pretty well in your example.

-Pascal