- 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 watercourse along which water is usually flowing. (2) A rivulet smaller than a river but larger than a brook.
Industry:Earth science
(1) An approximation to mean low water that has been adopted as a standard tidal datum for a specific region although it may differ slightly from a later determination. (2) The dynamic height for each of the Great Lakes and Lake St. Clair, and the corresponding sloping surfaces of the St. Mary's, St. Clair, Detroit, Niagara, and St. Lawrence Rivers, to which are referred the depths shown on charts and the authorized depths for improvements to navigation. Elevations of these datums are referred to International Great Lakes Datum (1955).
Industry:Earth science
(1) Control points which have accurately known horizontal coordinates (longitude and latitude), which can be identified with physical points on the ground, and which can be used to provide horizontal coordinates for other surveys. (2) A control station or stations whose horizontal coordinates have been determined. (3) The geometric data relating to the horizontal coordinates of a control station. For definitions of specific categories of horizontal control, see control, photogrammetric; traverse; triangulation; trilateration. The main purpose of lower order horizontal control is providing a transition from major geodetic networks to the control required for large scale mapping or for land surveying and engineering.
Industry:Earth science
The average interval between the transit of the Moon over the meridian of Greenwich and the time of strength of flood, modified by the times of slack water (or least current) and strength of ebb.
Industry:Earth science
A correction added to the observed time of an event to obtain the true time of the event.
Industry:Earth science
A curve composed of two circular arcs with a common tangent at their point of junction and lying on opposite sides of the tangent, that is with their centers of curvature on opposite sides of the tangent.
Industry:Earth science
A covered channel or pipe of large diameter taking a watercourse below the level of the ground or under an obstruction such as a road or railway.
Industry:Earth science
One of the two quantities: distance r from a central point of reference or direction θ from a specified line or plane of reference. Polar coordinates are related to plane rectangular coordinates x, y by x = r cos θ and y = r sin θ. The point of reference is called the pole, center or origin. The line joining the center to the point whose coordinates are wanted is called the radius vector. The angle from the fixed line or plane of reference and the radius vector is the vectorial angle, central angle or polar angle. In surveying, observations are usually put in the form of polar coordinates as a first step in computing coordinates in another coordinate system. For example, geodetic coordinates (longitudes and latitudes) are derived from measurements of distances and directions.
Industry:Earth science
The curvature of an ellipsoid chosen to represent the Earth. In surveying over short distances, if the Earth's curvature needs to be taken into account at all, representing the Earth by a sphere is adequate.
Industry:Earth science
