>Actually, it may be even simpler - if they are identical, just one rotated by 90 degrees over the other, then you can calculate this in a really simple manner: your x=y (or x=-y), so you can substitute y for x in the equation of either of them, solve it for y and that's it.

Good point. The intersect for identical perpendicular bisected elipses splits all the x,y's (-x,-y) at 45deg. so I did a rough plot with SIN(DTOR(45)) (which, BTW, also equals COS(DTOR(45)) for the x and y's.

I should have paid more attention when this stuff was fed to me!:-)