Meridian, guide -An auxiliary governing line projected north along an astronomical meridian from points established on the base line or a standard parallel, usually at intervals of 24 miles east or west o the principal meridian, on which township, section, and quarter-section corners are established. See also meridian assumed azimuth, assumed. Meridian, grid-A line through a point parallel to the central meridian or y-axis of a system of plane rectangular coordinates. used for the purposes of triangulation, a geodetic meridian is an till’s whose plane contains the minor axis of the ellipsoid, and whose geodetic azimuth at every point is 0° (south) or 180° (north). If the ellipsoid is an ellipsoid of revolution. Meridian, geodetic-A line on an ellipsoid which has the same geodetic longitude at every point. ![]() Meridian, convergence of-See convergence of meridians. The central meridian of the system usually passes close to the center of the figure of the area or zone for which the tables are computed. 3 The meridian used as the y-axis for computing projection tables for a state coordinate system. The central meridian is arbitrarily numbered 500,000 and is called a false casting. 2 The longitude of origin at the center of each zone of the Universal Transverse Mercator (1.1131) grid. Generally the basis for constructing the projection. Meridian, central- 1The line of longitude at the center of a projection. The intersection of the celestial meridian with the plane of II e horizon is the astronomic meridian line used in plane surveying. The plane of the celestial meridian is parallel with-but, because of the deflection of the plumb line, usually does not contain-the axis of rotation of the Earth. Also defined as the vertical circle which contains the celestial pole. Meridian, celestial -The hour circle which contains the zenith. Auxiliary guide meridians may be required to limit errors of old surveys or to control new surveys they are surveyed in all respects as are regular guide meridians. Meridian, auxiliary guide -A new guide meridian established, when required, for control purposes where the original guide meridians were placed at greater intervals than 24 miles. The astronomic meridian and the line whose astronomic azimuth at every point is south or north (0° or 180 0) are not necessarily coincident, although in land surveying the term “astronomic meridian” is sometimes applied to the north-south line which has its initial point on a prescribed astronomic meridian. Because the deflection of the vertical is not the same at all points, an astronomic meridian is an irregular line, not lying in a single plane. Meridian, astronomic–A line on the surface of the Earth with the same astronomic longitude at every point. See also meridian, grid azimuth, assumed. Meridian, assumed-A meridian chosen as a matter of convenience. The term usually refers to the upper branch, i.e., that half from pole to pole which passes through a given place the other half being called the lower branch. ![]() Meridian -A north-south reference line a great circle through the geographical poles of the Earth.
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