re sphere from points i plan to post a summary of responses to this as soon as i have working code which i will also include the intersection of planes method looks best but my implementation based on a short article in graphics gems i doesn t work i may be misinterpreting of course i had avoided the simultaneous solution of the plane equations in favor of dot and cross products but the former may actually be better in either case a matrix determinant needs to be computed implicitly in the solution of linear equations to get the planes i was taking the midpoint of the line from say p to p and setting the normal as the normalized vector from p to p these just plugged into the formula in graphics gems however the resulting center point is only occasionally equidistant from all of my test points for different tests my matrix vector math is very rusty but it looks like i need to verify the formula or use the simultaneous equation solution which will require bringing in another routine i don t have but should be easy to find another method is to first find the center of the circle defined by sets of points and intersecting the normals from there this would also define the circle center however small numerical imprecisions would make the lines not intersect supposedly planes have to intersect in a unique point if they are not parallel ed thanks to all who answered so far ed bolson university of washington cardiovascular research bolson u washington edu preferred bolson max bitnet bolson milton u washington edu if you must
