think you mean with reference specifically to ellipses? because it already works with the edges of other elements.

Sure. Specifically to ellipses.

1) if the neither Ellipse nor the line is constrained and I use point on line constraint with the end of the line and the edge of the Ellipse and then it moves the ellipse to meet the constraint requirements...this works but surprised me as I expected the line would be the element that would move.

Both partial derivatives are equal in value, the solver has the freedom to modify one or the other or both. If you lock the ellipse then it moves the line (but it could increase the major/minor axis of the ellipse to meet the line)... or both.

I can get a bug, if I try to place a line on the major and minor axes and I place the line somewhere close top what I want it works....to align them correctly I had to cheat by adding a directional length constraint of twice the major diameter to the line on the major axis and a perpendicular constraint on the two line so the other aligns with the minor axis. When phi can be set relative to a line rather than just x axis, then phi constraint would be the solution to use here.

Well this is not a bug IMHO, I guess you me twice the major semidiameter or twice the major radius... There are infinite solutions from both ends point on curve with or without going through the center point of the ellipse...

you could actually make a line at an angle with respect to X equal to the phi of the ellipse (set via constraint) and then make it pass thru center and then both extremes point on ellipse...

Now if I do the above but start with a line off to the right (relative x positive direction) and do a point on line constraint wit hthe closest end of the line it works as expected but if I then add the centre point of the Ellipse to the line with point on line constraint then it algins the line correctli but does not flip it into the correct direction

This is not a problem of ellipse implementation. Try to do the same with a circunference and you will have the same problem: it does not flip. It might be an issue of the point on line constraint implementation.

then I tried applying another point on line constraint to the other end of the line (end point) and the ellipse ...it still did not flip, it just gave me a conflicting constraints error and while in edit mode the line just disappeared, a view fit all did not show it.

This is interesting and is worth reporting it. If you can generate this situation systematically please file a mantis ticket (specially if with a circle the same happens)...

This is an example of what I was trying to achieve in the last post, if you create all the elements close to where they are supposed to be it did work.

Line not flipping is a problem of the line on point constraint. When thinking of the point on ellipse curve, you should think that the system is going to snap the point at the point of the ellipse that is closest to it. This might help...

Now that you managed to do it, you can remove any phi constraint and try to apply an angle to the ellipse by applying a normal angle constraint between the line on the major axis and the X axis (or another line)...

Hi! Sorry, I couldn't read the whole thread, but I want to emphasize the importance of ellipse focuses.

I do not blame you. It is too long

To me it makes sense, but as a generic functionality that would generate desirable construction lines and points of a geometry constrained to the actual geometry... for those who had technical drawing in high school: Do you know a graphical way of obtaining the focuses of an ellipse, given the ellipse and its center?