ACAD 2010 Drawing ellipse in a 3D 3point plane?

[just_jr]

I have a database of the 50 stars closest to the Sun.

I wrote a program that translates Right Ascension and Declination into X,Y,Z coordinates on the "normal" UCS view.

I created all stars in 3D, distances to scale (1m = 1Ly), stars as spheres 0.1Ly radius (so they are visible !)

Now, I need to draw the elliptic trajectory of a rogue "planet", starting near Lacaille8760 (6.456, 7.664, -8.076), passing near the EZAquarii, A, B & C, located at 3.557, 10.268, -2.973, to get a slingshot that will launch the planetoid towards the Sun (0,0,0). The elliptic trajectory should be a 3d "tube" a few pixels dia.

 

Problem:

How to set the screen coordinates to the plane formed by the 3 points above, so the ellipse can be drawn on a plane ?

I changed the UCS to 3 points, and the screen shows the three stars on the same plane, but when drawing the ellipse, it is to the original UCS...

 

I'll make the ACAD files available for download at http://r44.web2coders.com, "TECH" tab.

Once created, the drawing is used in R14 format to be imported in 3DSMax8 to get easier views and animation.

Any help welcome!