# Curvature Definitions for Land Surveyors

**curvature-**^{1}A curve; curved part of anything. ^{2} [GEOMETRY] The rate of deviation of a curve or curved surface from a straight line or plane surface tangent to it.

**curvature, normal—**The curvature, at a point on a surface of the curve which is the intersection of a plane through the normal to the surface and a tangent to the surface.

**curvature correction-**^{1}[ASTRONOMY] A correction applied to the mean of a series of observations on a star or planet to take account of the divergence of the apparent path of the star or planet from a straight line. ^{2} [GEODESY] The correction applied in some geodetic work to take account of the divergence of the surface of the Earth (ellipsoid) from a plane. In geodetic spirit leveling, the effects of curvature and of atmospheric refraction are considered together, and tables have been prepared from which combined corrections can be taken.

**curvature of field—**An aberration affecting the longitudinal position of images off the axis in such a manner that objects in a plane perpendicular to the axis are imaged in a curved or dish-shaped surface. See also *aberration of light *(definition **2)**.

**curvature of the Earth, correction for **[SURVEYING]-^{1} That offset from the tangent to the curve resulting from curvature of the Earth. The offset amounts to about 8 cm at 1 km distance. ^{2} That offset which is given in surveying tables as correction for curvature of the Earth. The values given in such tables usually combine the effects of both curvature the Earth and atmospheric refraction. Under normal conditions, the atmospheric refraction compensates partially for the curvature of the Earth, so the correction is about 6 cm for a point 1 km away.

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

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