"Anusha " <anusha@cs.usm.my> wrote in message <kai5qc$1ad$1@newscl01ah.mathworks.com>...
> Actually A and B represents points on a surface of medical structure. Capturing the medical structure at different time wil not provide an aligned point set representastion. I have checked this, and the structure A and B are not aligned at the same axis. thts why I need to aligned them to a common axis/center of gravity so tht further processing can be done.
- - - - - - - - - -
You are still making that same statement without defining what you mean! You have said, "I need to aligned them to a common axis/center of gravity". A set of points does have a centroid, we can agree on that, but that still leaves the point set with two degrees of freedom to rotate about that centroid. What do you mean by the "common axis" of the sets? I suggested using their principal moments of inertia which would indeed define a canonical set of orthogonal axes, provided all three were different, but so far you haven't responded to that suggestion. Do you have any other inherent axes that can be associated with a 3D point set? To put the question loosely, which way is inherently "up", which way is "in front", and which way is "to the side" for an abstract set of three-dimensional points of arbitrary orientation in some coordinate system?
Roger Stafford![]()
> Actually A and B represents points on a surface of medical structure. Capturing the medical structure at different time wil not provide an aligned point set representastion. I have checked this, and the structure A and B are not aligned at the same axis. thts why I need to aligned them to a common axis/center of gravity so tht further processing can be done.
- - - - - - - - - -
You are still making that same statement without defining what you mean! You have said, "I need to aligned them to a common axis/center of gravity". A set of points does have a centroid, we can agree on that, but that still leaves the point set with two degrees of freedom to rotate about that centroid. What do you mean by the "common axis" of the sets? I suggested using their principal moments of inertia which would indeed define a canonical set of orthogonal axes, provided all three were different, but so far you haven't responded to that suggestion. Do you have any other inherent axes that can be associated with a 3D point set? To put the question loosely, which way is inherently "up", which way is "in front", and which way is "to the side" for an abstract set of three-dimensional points of arbitrary orientation in some coordinate system?
Roger Stafford