How to find centre of an ellipse?

Rhino Rhino for Windows
1

Hi,
V5
I have some shapes on skin formed from projected circle onto a curving surface, result …they are eliptical.

I need to find centresof them then add points and use line normal then pipe and create circles on that surface instead.

What is best way to find centre of that apparent elipse, and admittedly as its a circle projected onto a surface curving in one direction they might not be perfect elipses as the surface was a bit wavy and I couldnt suss (lack of time etc) why it was so.

Steve

2

You could create a bounding box and find the centre of that. You would need to have the bounding box aligned to the ellipse which requires a script. Perhaps Pascal has that script?
Nick

3

This is probably too long-winded for you Steve, it will get your points though;

Temp copy of underlying surface
Split the copied surf at the curves
_AreaCentroid singly to each curve (repeat with enter)
This will place a point at each centroid on the current layer
Delete the copied surf

4

I expected that with Brian’s method after the points are created you would need to pull them to the surface before you can make your line normal, but it works just fine even though the points are not on the surface. Not quite as accurate, but quicker and possibly acceptable, would be to put points at centers of your original circles and then project them with the circles.

5

Should have said to each split surface - that would place the point on the surface wouldn’t it?

I agree with Mark that projecting the points in the first place would have been the way to go. The brain needs to be way ahead of the mouse clicks…

6

Can I assume that the original circles no longer exist?

7

Hi,
Original circles do exist, so I guess I could have projected point to surface from their centres, though I was thinking more generally anytime anywhere if I have an elipse or in perspective view looking at what I wanted to work on, I didnt want to exit the view, I could have gone 4 view then chosen the circle point projection above etc.

simplest method was as described below.

I see if its a drawn elipse Cen works…silly me.

However some interesting methods. thanks.

I tried this :-

select elipse on surface then used divide and then circle through points. Use the circle to find centre. It was good enough for what I needed though probably less technically correct than methods posted.

Steve