English

A line perpendicular to the FOCAL PLANE of the CAMERA and passing through the emergent nodal point of the LENS SYSTEM. Also called camera axis. See NODAL POINT.

In PHOTOGRAMMETRY, the intersection of the plane of the PHOTOGRAPH with the horizontal plane of the MAP or the plane of reference of the GROUND. Corresponding lines in the PHOTOGRAPH and map planes intersect on the axis of homology. Also called the axis of perspective, or map parallel.

The line tangent to the surface of a spirit level tube against which the bubble forms, at the centre of the graduated SCALE of the LEVEL, and in the plane of the tube and its centre of curvature. Also called level axis or spirit level axis.

A horizontal angle reckoned clockwise from the meridian. The horizontal direction of a celestial point from a terrestrial point, expressed as the angular distance from a reference direction. It is usually measured from 000° at the reference direction clockwise through 360°. An azimuth is often designated as true, magnetic, compass, grid, or relative as the reference direction is true, magnetic, compass, or grid north, or heading, respectively. Unless otherwise specified, the term is generally understood to apply to true azimuth which may be further defined as the arc of the horizon, or the angle at the zenith, between the north part of the celestial meridian or principal vertical circle and a vertical circle, measured from 000° at the north part of the principal vertical circle clockwise through 360°. When the angle is measured in either direction from north or south, and labelled accordingly, it is properly called azimuth angle; when measured either direction from east or west, and labeled accordingly, it is called AMPLITUDE.

The angle between the observer's MERIDIAN and the VERTICAL CIRCLE through the body, measured in the plane of the HORIZON. There is no universally accepted manner of reckoning the AZIMUTHS. Quadrantal, half-circle, and whole-circle methods are being used. In the latter, the AZIMUTH is measured preferably clockwise from north. See also AZIMUTH ANGLE.

The angle between the astronomic meridian plane of the observer and the plane containing the observed point and the VERTICAL of the observer.

An AZIMUTH 180° from a given AZIMUTH. In GEODESY, the DIRECTION of the line BA as distinguished from the forward azimuth AB. The two differ by 180° plus the amount of CONVERGENCE OF THE MERIDIANS between points A and B. Also called reverse azimuth. See AZIMUTH: GEODETIC.

For the GEODESIC LINE from A to B, the angle between the tangent to the MERIDIAN at A and the tangent to the GEODESIC LINE at A. This AZIMUTH is called the forward azimuth for the line AB. See AZIMUTH: BACK.

At the point of OBSERVATION, the angle between the VERTICAL PLANE through the observed object and the VERTICAL PLANE in which a freely suspended symmetrically magnetized NEEDLE, influenced by no transient artificial magnetic disturbance, will come to rest.