Originally Posted by

**cptn_gnd** hi all

for any 3 points in 3d space. (x1,y1,z1) etc there is a unique circle that can be drawn throught then. I have spent many hours trying to derive the equasion of that circle so that I can then find the intersection of the plane Y=a and that circle but have not got anything clean, the approach that I have tried is to translate and rotate the coordinate system so that the 3 points all lie on the plane z=0 then use a reverse transformation to get the actual intersection, this is horendous does anyone have a better approach, any assistance would be of help I'm stumped