- Branche: 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 amount by which the sum of the directed excursions north and south of a line running east and west fail to add up to the directed distance of the final station; in particular and usually, the amount by which they fail to add up to zero upon return to the original station.
Industry:Earth science
That portion of the overlap of a pair of photographs which is actually used in a photogrammetric mapping project. Usually, the neat model is nearly rectangular with a width equal to the air base and length equal to the distance (width) between flights.
Industry:Earth science
(1) A map showing events involving motion, action, or change. A dynamic map involves time. The term may be applied to maps depicting the flow of traffic, migration, military movements, progress in an engineering project, historical geography and so on. Various symbols, such as flow lines and arrows, are used to show movement. A dynamic map may also be composed of two or more static maps, showing comparable data at stated but different times or dates. (2) A map on which changes take place. A map showing continental drift by having the images of continents actually move about would be a dynamic map. A dynamic map may be created by photographing a sequence of maps, each map showing a different stage in the sequence of events, and then displaying the photographs as a moving picture; or by creating a digital map, displaying the re-created map on the screen of a cathode ray tube, and using a computer to make the necessary changes from instant to instant.
Industry:Earth science
A map having on it graphical information regarding administrative matters such as supply, medical facilities or boundaries.
Industry:Earth science
An invariable pendulum, one-quarter meter long, with a period of vibration of one-half second, and consisting of a lenticular bob on a thin stem, swung in near vacuum in an airtight case. The pendulum was designed in 1890 by Mendenhall and assistants of the U.S. Coast and Geodetic Survey.
Industry:Earth science
(1) The amount, obtained using Molodensky's formulas, to be added to the length of a geodesic between two specified points on the geoid to obtain the length of the geodesic between the two corresponding points on that ellipsoid taken to represent the geoid. In older methods of calculating coordinates in triangulation networks, the length of the measured base line on the ground was reduced to its equivalent length on the geoid, but this length was then assumed to be the length of the corresponding geodesic on the ellipsoid. The Molodensky correction eliminates this error. (2) The amount (h - h <sub>c</sub>) to be added to the assumed height h <sub>c</sub> of the geoid above the ellipsoid to obtain the actual height h, as given by Molodensky's formulas.
Industry:Earth science
An existing feature, such as a stone, stake, tree, hill, ocean, river or lake, considered as a monument.
Industry:Earth science
The interval of time between two successive passages of the Moon through that great circle which contains the celestial poles and passes through a specific star. The sidereal month can be measured by the length of time it takes the Moon to revolve from a given celestial longitude back to the same longitude, reckoned from a fixed equinox. It contains, on the average, 27.321661 mean solar days. Because the orbit is perturbed, the actual length of time varies some 7 hours. The difference between the lengths of the sidereal and tropical months is caused by the precession of the equinoxes.
Industry:Earth science
A measure of the brightness of a celestial object relative to the brightness of a standard, i.e., to a brightness of specified value. Usually referred to simply as magnitude if the meaning is clear. The concept was first introduced by Hipparchus in 150 B.C. He designated the 15 brightest stars as stars of the first magnitude and stars just visible to the naked eye as stars of the sixth magnitude. The idea was extended by Ptolemy (150 B.C.) and given its modern form by Pogson in 1856. To keep Hipparchus's scheme as intact as possible, John Herschel, about 1830, made a difference of 5 magnitudes equivalent to a ratio of exactly 100 in brightness. In other words, two stars differing in magnitude by 5 differ in brightness by a ratio of exactly 100 to 1. Any particular object will have several magnitudes, depending upon what portion of the object's spectrum is used for viewing. Unless specifically stated otherwise, the object is assumed to be viewed in the optical part (light) of the spectrum and apparent magnitude is ordinarily meant. If several parts of the spectrum are being considered, the term visual magnitude is used for the magnitude of the object as seen in light. (Note that although the term is stellar magnitude, it is applied also to non stellar objects.)
Industry:Earth science
