Sorry for the long reply time, got caught up in other stuff.

Jean, the pointer to the tutorial that you left is just what I needed, thanks. I would have thought that it wouldn't be necessary to go through such a rigamarole, but, if it gets the job done.

Thanks again for all of the help,

Greg

Jeff, thanks for the concern, the output from SU isn't going to be used for grinding a lens. Right now I need to find out the shape of the mirror so that I can figure out what the holding structure is going to look like and if it's going to work out ok. It's just that I need to define the curve from the foci not from a bounding box.

Greg

Jim, thanks for the post, I had searched for this tool before and had not found it. Unfortunately, while Dider's description of an elipse is exactly what I need, the script doesn't work that way, it uses the 'major' and 'minor' axis lengths.

I guess, even though I don't know Ruby, I'll try to understand Dider's script enough to change it to work the way that I need it to work.

Greg

Thanks for the suggestion Dylan, but as I said in my OP, I know the two focus points that I need, and one point on the curve. I don't know what the curve looks like and I can't define a bounding box for it. With the method that you suggest I can define the original focus point as the center of the circle and the point on the curve as the radius, but I don't know as I'm scaling it where the second focus point is. This is critical, I'm trying to define the inside of a concave mirror to reflect light from the first focus point to the second focus point so I need to be able to specify the elipse based on the focus points and the curve point.

Greg

Hello all, I just getting started using SketchUp and already seem to have come across a problem. I would like to draw an elipse where I know 2 focus points and one point on the curve. Mechanically generating a this curve is very straight forward, if I were doing it on a piece of wood I'd anchor a piece of string to the two focus points and adjust the length so that a pencil holding the line tite would sit the known point of the curve, then just run the pencil from one end starting on a line intersecting the focus points out to one side and down to the other end (I hope that makes sense, see here for another description).

SketchUp doesn't seem to have a tool for drawing elipses and I haven't been able to find any talk of ways to generate one in this fashion on any of the SketchUp help pages or forums.

Thanks in advance for any tips or pointers that you can pass on to this neophyte,

Greg