- Industry: 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, ...
(1) A plane perpendicular to the direction of gravity at a given point. Equivalently, a plane tangent to a level surface at a given point. In general, a horizontal plane is perpendicular to the direction of gravity only at the point at which it is defined. The term is not synonymous with plane of the horizon; the plane of the horizon is defined by the horizon, not by the direction of gravity. (2) A plane parallel to a plane tangent to the geoid at a given point. (3) A plane perpendicular to the direction of gravity at a given point and within which or one which angles and distances are measured. For any planimetric survey, the direction of gravity at all points of the survey is assumed to be constant and all horizontal planes therein are parallel.
Industry:Earth science
A survey traverse made using a plane-table to determine angles and directions. A surveyor's tape is usually used to measure distances, although a stadia rod may be used (with the proper type of alidade).
Industry:Earth science
An alidade consisting of a telescope mounted on a straightedge and having a pendulum instead of a spirit level for establishing the direction of the horizontal line or reference for vertical angles.
Industry:Earth science
(1) The angular coordinates of a celestial body. (2) The location of a celestial body on the celestial sphere.
Industry:Earth science
A geodesic on an ellipsoid; in particular, a great circle. The term is obsolete.
Industry:Earth science
That point, in a reflecting telescope, at which light is focused by inserting a flat mirror at 45<sup>o</sup> to the principal axis of the primary mirror. Light is thus brought to a focus at the side of the telescope, not in back of the primary as with a Cassegrainian focus or at the end of the polar axis as with a coudé focus.
Industry:Earth science
A mechanical linkage for plotting true horizontal directions from oblique aerial photographs.
Industry:Earth science
Oblique photography, usually done with a pair of cameras acting as a unit, so that one photograph is taken looking forward along the line of flight and the succeeding, overlapping photographs taken looking back along the line of flight. Convergent photography can provide photographs with a much larger base height ratio, but it is much more difficult to carry out than vertical photography.
Industry:Earth science
The distance from the mid-point of a chord to the mid-point of the corresponding circular arc.
Industry:Earth science
A sheet accompanying the manuscript of a map and carrying only such information as names of features, descriptive labels, classification of symbols for roads and drainage and explanatory notes.
Industry:Earth science
