Corrected entry: Dr. Jackson states that you need six points in a 3D volume to define a unique position. He then draws six points on the faces of a cube and connects the opposed pairs of points with lines, demonstrating that they all intersect to reveal the unique location. Whether this is really a good way to identify points in space is debatable, but even so, the technique he demonstrated requires only four points, not six. Any two lines that intersect do so at a unique point.
Jefficus
13th May 2009
Correction: Four points could only produce two intersecting lines that define a certain coordinate in a 2-dimensional plane (a flat surface). Six points are required to produce three intersecting lines that define a certain coordinate in a third dimension (depth).
Charles Austin Miller