- Industry: 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 approximation V ≈ -(GM/r)(1 + (A + B + C - 3I)/(2Mr²)) to the gravitational potential V at a distance r from the center of mass of a body whose mass is M, whose moments of inertia about the principal axes are A, B and C, and whose moment of inertia about the line from the center of mass to the point in question is I. G is the gravitational constant.
Industry:Earth science
That meridian, lying west of Greenwich, at which the beginning of the Besselian year coincides with the beginning of the Julian year. The Besselian year begins at the same time all over the world. For example, the Besselian year 1966.0 began on 1966 January 0.799d Greenwich mean sidereal time. At this instant, the Julian date was 1966 January 0.00d on the meridian at 72.36 degrees West.
Industry:Earth science
The angle between the plane of the reference meridian and the plane of the meridian of a point on the Earth.
Industry:Earth science
A device, apparatus, or equipment more or less permanently emplaced at a known location to assist in navigation.
Industry:Earth science
The dihedral angle between two planes parallel to the least axis of an ellipsoid. The angle is taken counterclockwise, as viewed from the north, from one plane used as reference to the plane containing the normal at the point of interest. Also referred to a longitude if the meaning is clear. The reference plane is usually specified in one of three ways. (a) It contains the normal at some specified point on the ellipsoid. (b) It contains the least axis of the ellipsoid and is parallel to the normal at the specified point. (c) It contains the least axis and the specified point. Properly, only (a) should be used; (b) and (c) are more appropriately used for geocentric longitudes. However, all three ways are identical if the ellipsoid is rotationally symmetrical. A geodetic longitude on the rotational ellipsoid can be measured by the angle, at one of the poles of the ellipsoid, between local and initial meridians, or by the arc intercepted by these meridians on the equator. A geodetic longitude differs from the corresponding astronomic longi-tude by the amount of the component, in the prime vertical, of the local deflection of the vertical divided by the cosine of the latitude. In the USA, this may be as much as 25". In recording a geodetic longitude, the datum to which it is referred must be stated. In the USA, before the introduction of the North American Datum of 1983, geodetic longitudes were numbered from the Meridian of Greenwich but were computed from the meridian of station Meades Ranch as prescribed by the North American Datum of 1927.
Industry:Earth science
An aerial mosaic composed of photographs mutually oriented by reference to some coordinate system other than that determined by ground control.
Industry:Earth science
A fictitious observatory situated on the Greenwich Mean Astronomical Meridian. I.e., a fictitious, ideal observatory situated so that times determined by it are exactly the same as the times established by the Bureau International de l'Heure as the average of times determined at many real observatories.
Industry:Earth science
A pattern of measurements in the field, such that the final measurement is made at the same place as the first measurement.
Industry:Earth science
