- 行业: Earth science
- Number of terms: 93452
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Founded in 1941, the American Congress on Surveying and Mapping (ACSM) is an international association representing the interests of professionals in surveying, mapping and communicating spatial data relating to the Earth's surface. Today, ACSM's members include more than 7,000 surveyors, ...
(1) A coordinate system consisting of the celestial equator and of a selected celestial meridian; or, equivalently, of one plane perpendicular to the Earth's axis of rotation and another plane parallel to that axis and passing through the vertical at a specified point. The coordinates of a point on the Earth's surface are determined by the meridional arc between the equator and the point, and by the equatorial arc between the selected meridian and the meridian through the point. (2) A coordinate system the same as that of the preceding definition except that the coordinates of a point on the surface are those of that point which is vertically above or below it on the geoid. (3) A coordinate system the same as that in (2) except that an average position of the Earth's axis of rotation is used. This coordinate system is sometimes referred to as a reduced astronomic coordinate system; the coordinates are then referred to as reduced astronomic coordinates. (4) A coordinate system in which the locations of celestial bodies (Sun, planets, stars, etc. ) are given. An astronomic coordinate system is also called an astronomical coordinate system.
Industry:Earth science
(1) The change (δg <sub>c</sub>) in the calculated value of gravity, on the reference surface, when matter in the form of a thin disk, radius r at depth D below that surface is removed. The matter in the disk is used, after applying a free air gravity correction, to fill the Bouguer cylinder. The mass M in the Bouguer cylinder is given by M = ρπr²h, in which h is the height of the cylinder, r the radius and ρ the density of the matter in it. The change δg <sub>c</sub> (in newtons per kilogram or meters per second²) is δg <sub>c</sub> = 2GM (((h+D)/ √(r ² +(h+D)²) - 1)/r ², in which G is the gravitational constant. (2) The same as the preceding definition but with elevation H being used instead of height h, the geoid being used as the reference surface. (3) The same as either of the preceding definitions, but with the condensed mass lying in a thin layer on a surface parallel to the reference surface and equal to the topographic masses outside that surface.
Industry:Earth science
In the relative orientation of two photographs, the cumulative warpage of the models affecting the vertical datum because of errors introduced by x-tilt and y-tilt.
Industry:Earth science
A coordinate system, in the plane, in which the coordinates are given as the inter-sections of a family of numbered confocal ellipses and numbered confocal hyperbolae.
Industry:Earth science
A network consisting of control stations whose locations have been determined by astronomic measurements. The astronomic longitudes and latitudes will normally differ from the geodetic longitudes and latitudes of the same stations by amounts corresponding to components of the deflections of the vertical.
Industry:Earth science
(1) A point to which coordinates have been assigned, these coordinates then being used in other, dependent surveys. The term is sometimes used as a synonym for control station. However, a control point need not be realized by a marker on the ground. (2) A point which is identifiable on a photograph, to which coordinates have been assigned, and which is used in determining the scale and absolute orientation of the photograph. The term is usually modified to indicate the type or purpose of the point, as, for example, ground control point, photocontrol point and vertical control point.
Industry:Earth science
A spherical coordinate system which has its polar axis coincident with the axis of the dipole representing the Earth's magnetic field. The zero meridian is usually selected to pass through the astronomic or geodetic North Pole.
Industry:Earth science
The quantity 1 m²/s². It is not, even approximately, the same as the amount of work done in lifting a unit mass one decimeter.
Industry:Earth science
The acceleration produced by the Coriolis force (q. V. ).
Industry:Earth science
(1) A current station from which a relatively short series of observations is reduced by comparison with simultaneous observations from a control current station. (2) A station listed in the Tidal Current Tables for which predictions are to be obtained by means of differences and ratios applied to the full predictions at a reference station.
Industry:Earth science
