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Ptolemy used a circle of diameter 120, and gave chord lengths accurate to two sexagesimal (base sixty) digits after the integer part. [2] The chord function is defined geometrically as shown in the picture. The chord of an angle is the length of the chord between two points on a unit circle separated by that central angle.
A scale of chords may be used to set or read an angle in the absence of a protractor. To draw an angle, compasses describe an arc from origin with a radius taken from the 60 mark. The required angle is copied from the scale by the compasses, and an arc of this radius drawn from the sixty mark so it intersects the first arc.
The term contrast ratio may be preferred for the luminance range in a scene. [14] DSC: Digital Still Camera. Prefix on image filenames produced by various digital cameras. DSLR: Digital single-lens reflex camera; also dSLR. [2] ED: Extra low dispersion glass. Used in composite lenses to reduce chromatic aberration.
Ptolemy used geometric reasoning based on Proposition 10 of Book XIII of Euclid's Elements to find the chords of 72° and 36°. That Proposition states that if an equilateral pentagon is inscribed in a circle, then the area of the square on the side of the pentagon equals the sum of the areas of the squares on the sides of the hexagon and the ...
Ptolemy used chord length to define his trigonometric functions, a minor difference from the sine convention we use today. [12] (The value we call sin(θ) can be found by looking up the chord length for twice the angle of interest (2θ) in Ptolemy's table, and then dividing that value by two.)
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Definition: In the context of photography, is the measure of the total energy, or quantity, of eye-adjusted visible light that impinged upon a unit area over a specified period of time. In common vernacular, it is the product the brightness of light measured at the surface of a photographic subject times the duration of that light.
Low altitude aerial photograph for use in photogrammetry. Location: Three Arch Bay, Laguna Beach, California. Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant imagery and other phenomena.