- Industri: Earth science
- Number of terms: 93452
- Number of blossaries: 0
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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 sight to a previously established point of a survey, or the reading or measurement obtained by that sight. (2) In leveling from an initial point to a final point through a sequence of intermediate points, a sight to (or the reading on) a leveling rod held on a preceding point. The sight to, or reading on, a leveling rod held on the succeeding point is called the foresight. In leveling, a backsight is sometimes called a plus sight because its value is added to the elevation of the point on which the leveling rod is placed, to obtain the elevation of the leveling instrument. But if the sight is to a mark on a wall or is in the roof of a mining tunnel, with the instrument at a lower elevation than the mark, the backsight will be subtracted from the known elevation to obtain the height of the instrument. The term backsight is preferred over plus sight. Neither of these definitions requires that the point or leveling rod to which the sight is made be one whose coordinates have been defined or determined previously. If the sequence consists of only two points, it is a matter of indifference which is called the backsight and which the foresight. (3) The visual intersection of the horizontal crosshair of a leveling instrument with a staff or leveling rod held vertically over or under the preceding point when the line of sight is horizontal or when the vertical angle of the line of sight is known or will become known from actual measurement. (4) The angle measured on the horizontal circle of a surveying instrument (set or to be read and recorded) when the vertical crosshair of the instrument coincides visually with the preceding point and the center of the instrument.
Industry:Earth science
(1) The acute angle between a line perpendicular to one center-line and to another center line. (2) The amount of angle by which that two intersecting lines deviate from a right angle.
Industry:Earth science
(1) The number of times the apparent topocentric, angular diameter of a celestial body is greater than the geocentric, angular diameter of that body.
(2) The apparent increase in diameter of a celestial body as its angular elevation increases, because the body is closer to the observer. This should not be confused with the apparent increase in size of the Moon or Sun at the horizon as compared to the size when well above the horizon. This latter phenomenon seems to be psychological rather than physical in nature.
Industry:Earth science
The angle, on the celestial sphere, between a great arc from a heavenly body to the pole and a great arc from the celestial body to the observer's zenith. It should not be confused with parallax.
Industry:Earth science
A theodolite of low accuracy with limited amount of rotation vertically, a low power telescope, and containing a magnetic compass. Aiming circles used by the artillery have been graduated in mils. Used in horizontal surveys, such an instrument can provide an accuracy of about 1:500.
Industry:Earth science
(prefix) Farthest from the attracting body. e.g. apogee, that point, in the elliptical orbit of a terrestrial satellite, at which the satellite is farthest from the Earth. But aphelion, not apohelion, is customary.
Industry:Earth science
An owner or occupant whose property adjoins or touches the land under consideration.
Industry:Earth science
(1) The process of using an autocollimator. (2) The procedure used to determine or transfer azimuth to an instrument or device by using an autocollimator.
Industry:Earth science
A device which can be attached to an engineer's transit or other kind of theodolite, to permit the instrument's use as a solar compass.
Industry:Earth science
An attachment to the telescope of a leveling instrument, consisting of a wedge shaped prism rotatable about an axis parallel to the optical axis of the telescope and deflecting the line of sight. It is used in certain techniques devised particularly for leveling across valleys, rivers, and large bodies of water.
Industry:Earth science
