horizontal angle—See angle, horizontal.

horizontal axis—The axis about which the telescope of a theodolite or transit rotates when moved vertically. The axis of rotation is perpendicular to the vertical axis of the instrument and to the axis of collimation of the telescope. It should coincide with the line through the centers of the pivots which support the telescope. For an instrument in complete adjustment it occupies a horizontal position, and when the telescope is rotated around it, the axis of collimation defines the vertical plane; deviations from this condition are measured with a striding level or with a hanging level.

horizontal closure error—See error of closure.

horizontal control—See control, horizontal.

horizontal control station—See control station, horizontal.

horizontal datum—See datum, horizontal.

horizontal directions—See direction.

horizontal distance—See distance, horizontal.

horizontal plane—See plane, horizontal.

horizontal refraction—See refraction, horizontal; refraction, terrestrial.

–

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

Part of LearnCST’s exam text bundle.