observation—Act of recognizing and noting a fact or occurrence, especially in nature, often involving the measurement of a magnitude with suitable instruments.

observation, direct—A measure of the quantity whose value is desired (for example, a single measure of a horizontal angle).

observation, indirect—A measure of a quantity which is a function of the quantity or quantities whose value is desired. An example is an observed difference of elevation with a spirit level used to obtain the elevation of a benchmark.

observation, solar-In astronomical geodesy, a measurement of the Sun’s angular elevation, right ascension, time of crossing a particular plane, etc.

observation equation—See equation, observation.

observed value—A value of a quantity that is obtained by instrumental measurement of the quantity. Often applied to the value of a quantity derived from instrumental measurement after corrections have been applied for systematic errors, but before accidental errors have been taken out by some method of adjustment. See also value. most probable; adjustment (definition 1).

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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