- 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, ...
The horizontal angle, measured clockwise, from the preceding leg of a traverse to the following leg.
Industry:Earth science
A method of adjusting a triangulation network, using adjustment by conditions, in which the measurements are of angles and the unknowns are corrections to the measured angles. The angle method is similar to the direction method, in which the corrections are to measured directions (azimuths). The angle method should be used where a chain of single triangles is to be adjusted. For an extensive network with overlapping triangles, the direction method of adjustment is preferred.
Industry:Earth science
A rectangular tube to one side of which is fastened a vertical, graduated arc with vernier and carrying a rotatable level. The instrument is small and light enough to be held in the hand. When used as a leveling instrument, the vernier is set at zero on the graduated arc. When used to determine vertical angles, the object is sighted through the tube and the vernier rotated until the bubble is centered in the vial. The angle is then read off the graduated arc. This leveling instrument is named after W. deW. Abney, an English physicist and, with Locke's level, is one of the best known of its type.
Industry:Earth science
(1) A diameter of the Earth, drawn between two points on the Equator. (2) A line drawn thru the center of an ellipsoid, in a plane perpendicular to the shortest axis of the ellipsoid, and extending from one side of the ellipsoid to the other. (3) An axis, in the mounting of a telescope, which is parallel to the plane of the equator.
Industry:Earth science
The azimuth of a line at the end (the end point) opposite that used for reference. If, on an ellipsoid, the azimuth of point B from point A is given, the back azimuth is the azimuth of point A from point B. Because of the meridional convergence, the forward and back azimuths of a line do not differ by exactly 180° except where A and B have the same geodetic longitude or where the geodetic latitudes of both points are 0°. If the two points are on a plane, in a rectangular Cartesian coordinate system, the same relationship between forward and back azimuths holds, but the two azimuths differ by exactly 180°.
Industry:Earth science
(1) A body of water held back from its natural course by some obstruction such as a contrary current, dam, etc.
(2) A region affected by water held back from its natural course by some obstruction.
Industry:Earth science
Any instrument used for measuring angles. Sometimes called an angulation instrument. Examples are the goniometer, the theodolite, the transit, and electronic devices which measure angles by interference of radio waves. Although photogrammetric cameras and plotters are used for determining angles, they do not indicate the angles directly and hence are not classified as angle measuring instruments.
Industry:Earth science
An ambiguity which appears on the face of the instrument and arises from the defective, obscure, or insensible language used.
Industry:Earth science
A lack of symmetry in the appear-ance of an object as seen from a particular point of observation, and caused by an actual asymmetry in the object or its aspect. It causes an object to appear differently when viewed from different points and can result in different points of the object being sighted at from different points of observation. A square or rectangular pole may face the observer in such a way that a line bisecting the angle made by lines of sight tangent to the pole's edges does not pass through the center of the pole. If, instead of a pole, a square cupola or tower is sighted on, the error may be quite large. The error caused by observing on such objects is of the same character as the error caused by observing an eccentric object. Asymmetry of object differs from phase in that the former is caused by an actual asymmetry of the object as viewed; the latter is caused by an asymmetric illumination of the object.
Industry:Earth science
A printing process using a zinc plate which is gelatin coated, hardened, and sensitized to print type, line drawings, and halftones by an offset process.
Industry:Earth science
