- 行业: Earth science
- Number of terms: 93452
- Number of blossaries: 0
- Company Profile:
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, ...
A graphic representation of a rotary current in which the velocity of the current at different hours of the tidal cycle is represented by vectors. The cycle may be completed in one half tidal day or in one tidal day according as the tidal current is semi diurnal or diurnal.
Industry:Earth science
(1) A point, on the ground, whose location (horizontal or vertical coordinates) is used as a basis for obtaining locations of other points. (2) A survey station whose coordinates are accepted as being sufficiently accurate that the coordinates of other survey stations can be determined with reference to it. In other words, a survey station used for control. (3) A point on the ground whose location (horizontal or vertical or both) is used as a basis for a dependent survey, and from which observations were made.
Industry:Earth science
(1) A graduated arc, on a surveyor's solar compass or on the solar attachment of an engineer's transit, on which the declination of the Sun (corrected for refraction) is set off. (2) A graduated arc, attached to the alidade of a surveyor's compass or transit, on which the magnetic declination is set off. A reading of the needle will give a bearing corrected for that declination.
Industry:Earth science
The angle ζ', at the point P' which is on the geoid and vertically below the point P on the Earth's surface, from the normal at the reference ellipsoid to the vertical through P'. Because P' is not accessible, the directions of both normal and vertical must be calculated.
Industry:Earth science
A horizontal plane at the average elevation of the terrain shown in a photograph and on which distances measured will be approximately proportional to corresponding distances measured on the photograph.
Industry:Earth science
A lens system which concentrates the light from a source onto a limited area. An ellipsoidal reflector having the source at one of its foci concentrates the light at the other focus and is optically equivalent to a condenser.
Industry:Earth science
A correction made to the period of a pendulum to account for effects of the Earth's rotation: centrifugal force, Coriolis acceleration, tilting of the pendulum's plane of motion and differing angular accelerations of different supports.
Industry:Earth science
The joining of two separate triangulation networks into a single network without internal discrepancies.
Industry:Earth science
Failure of the optical center of one element of an optical system to lie on the optical axis of a preceding or succeeding element. Decentration causes distortion, tan-gential distortion in particular, similar to that caused by introducing a thin wedge into a perfectly centered optical system. Decentration is therefore sometimes called the wedge effect.
Industry:Earth science
