Concept

Leverage — where it appears

How much one measurement influences a fitted answer, which depends on where it sits rather than on how carefully it was read. A reference at the edge of the data carries disproportionate weight, so a wrong value there does more damage than the same value in the middle.

Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.

Which reference to measure from

Given four candidate scale bars in one photograph, the best is not the longest and not the nearest — it is the longest in the picture. A five-point-two metre bar near the horizon is the longest thing in the scene and the worst reference in it; a four metre bar close to the camera is the best. Walk one bar outward and the term it controls falls as one over its length in pixels, with a fitted exponent of −1.08.

metrology · Uncertainty

The arrangement the count cannot see

Five posts laid out five different ways give the same leverage to a sixth and the same separation limit to a quarter, and the sixth arrangement — posts strung out along their own shadows, built to be exactly degenerate — is no worse than the rest. The degeneracy belongs to the family the count does not use, and its conditioning there is exactly zero.

light · Pointcount

Named alongside it

The objects these essays reach for when they reach for this one.

Conditioning Bias Degenerate configuration Depth uncertainty error propagation Homography Identifiability Light recovery Null result Point light Rectification Reference length

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