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Seven diagrams and a near-equilateral expansion connect shape to position.
Drag the three large vertex handles, or focus a handle and move it with the arrow keys. Select centers to overlay their locations. The two other views explain the physical definitions and compare their shape fingerprints.
A triangle center must commute with rigid motions, scaling and vertex relabeling. An attractive center moves in a nonnegative projected direction when one vertex is displaced: δv · δc ≥ 0.