Visual Plane
every picture states the point it is correct from
Concept

Cross-ratio test — where it appears

Checking that four drawn points have the cross-ratio a real projection would give them, which a plausible drawing need not. It is only worth running where the value it is checked against could have come out otherwise: four consecutive divisions of a receding row pass it whether or not the drawing is right.

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

horizonequal stepshalve thetaper byworst error, in metres of depthequal steps to the horizon11.72 mhalve the remaining gap225.13 mtaper by eye347.80 mcorrect from 26 cm, at 160 mm wide34° across

Dividing depth by eye

Three methods for spacing a receding row, all of them taught, all of them wrong. Read back as distances, the best misplaces a post by 3.5 metres in a row that is supposed to be spaced 1.4. And the obvious way of checking them gives one of the three a perfect score.

wrong · Deptheye a centretrue measurediminutionbounded depthstraight linesperspectivehandscrollisometricdimetrictrimetriccavaliercabinetelevationmilitaryfilled means the system keeps itmeasured from each system's own projectionno row is filled in both of the first two

Each system answers its own question

A comparison in which every system wins its own column proves nothing if the columns were chosen after the systems. The test that makes it a result is whether any system wins something it was not designed for — and two of them do.

choices · Exclusion

Named alongside it

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

necessary, not sufficientAxis scaleConformalDemonstrationDepth divisionDiminutionDrawing systemFree parameterHorizoninstrument limitInverse projectionMeasuring point

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