Axis Definitions for Land Surveyors

axis- 1A straight line about which a body rotates, or around which a plane figure may rotate to produce a solid; a line of symmetry. 2One of a set of reference lines for certain systems of coordinates. 3The principal line about which anything may extend, as the axis of a channel or compass card axis. 4A straight line connecting two related points, as the poles of a magnet.

axis, bubble—The horizontal line tangent to the upper surface of the centered bubble, which lies in the vertical plane through the longitudinal axis of the bubble tube; axis level vial.

axis, collimation—See collimation axis.

axis, optical—See optical axis.

axis of homology-1 In geometry, the intersection of two projectively related planes. 2In photogrammetry, the intersection of the plane of a photograph with the horizontal plane of a map or the plane of reference of the ground. Corresponding lines in the photograph and map planes intersect on the axis of homology.

axis of sighting—The line drawn through the optical center and centers of curvature of the lenses of a telescope. See also collimation, line of

axis of tilt—A line through the perspective center perpendicular to the principal plane.

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

Part of LearnCST’s exam text bundle.