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

Quantisation — where it appears

Storing a continuous quantity as one of a finite set of values, which destroys distinctions finer than the step.

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

00.2500.5000.7501-10123distance from the eye — log₁₀ metresfraction of the buffer's codes used uphalf the codes by 0.20 ma linear map, for comparisonnear 0.1 m, far 1000 mharmonic mean 0.20 m against arithmetic 500 m

The precision a depth buffer has left

Depth is stored as an affine function of one over the distance, so half of a buffer's codes are spent before the harmonic mean of the near and far planes — twenty centimetres out of a kilometre. The resolution goes as the square of the distance, and the fix that works is not more bits.

pipeline · zbuffer one pixel is an areacentrescornersprincipal point moves0.707 pxfocal length changes by4.5e-13 pxan edge-versus-centre viewport1.303 pxa half-pixel convention is a principal-point error; an off-by-one viewport is a focal-length error8 vertices, all shifted by the same 0.7071 pxspread across marks 0.0e+0 px

A pixel is not a point

Where the sample sits inside a pixel is a convention, and getting it wrong shifts every mark by half a pixel in each axis. This site can say what that costs, because it recovers cameras from pictures — the answer is a principal point exactly 0.707 px from the truth with the focal length untouched, and the other half-pixel mistake does precisely the reverse.

pipeline · viewport

Named alongside it

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

Camera matrixDemonstrationResidualCamera calibrationClip spaceConditioningDepth bufferFocal lengthHomogeneous coordinatesinstrument limitOcclusionPrincipal point

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