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An electronically-generated cross hair used to indicate a position on a raster scan display.

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A picture cell, one of thousands of pinpoints of light that make up the picture on a raster scan radar display.


As defined by the International Telecommunication Union (ITU), a transmitter in the aeronautical radionavigation service which radiates vertically a distinctive pattern for providing position information to aircraft.


  1. The process of towing a line or object below the surface, to determine whether an area is free from isolated submerged dangers to vessels and to determine the position of any dangers that exist, or to determine the least depth of an area. 2. The process of clearing an area or channel of mines or other dangers to navigation.


A satellite navigation system developed by the Department of Defense. The system is provides highly accurate position and velocity information in three dimen- sions and precise time and time interval on a global basis continuously, to an unlimited number of users. It is unaffected by weather and provides a worldwide common grid reference system. The objective of the program is to provide very precise position information for a wide spectrum of military missions. In addition, current policy calls for civil availability with a slight degradation in system accuracy required to protect U.S. national security interests.


Extension boarding at deck level to increase the width of the hull of a sailing ship for the lower stays land upon, thus providing a wider angle of mast support. The traditional position from which a seaman heaved a hand lead line (to establish depth).


  1. A plane closed curve all points of which are equidistant from a point within, called the center. A great circle is the intersection of a sphere and a plane through its center; it is the largest circle that can be drawn on a sphere. A small circle is the intersection of a sphere and a plane which does not pass through its center. See also PARALLEL OF ALTITUDE, PARALLEL OF DECLINATION, PARALLEL OF LATITUDE; AZIMUTH CIRCLE, BEARING CIRCLE, DIURNAL CIRCLE, EQUATOR, HOUR CIRCLE, PARASELENIC CIRCLES, POSITION CIRCLE, SPEED CIRCLE, VERTICAL CIRCLE. 2. A section of a plane, bounded by a curve all points of which are equidistant from a point within, called the center.


To observe and plot lines of position locating an object or craft, particularly by bearings


An optical device used to superimpose the plan position indicator radar picture on a navigational chart.


A method for determining the position of an unknown station position when the unknown position cannot be viewed simultaneously with known positions. The arc of the satellite orbit is extrapolated from the ephemeris of the satellite determined by the known stations which permits the determination of the position of the unknown station dependent completely on the satellite’s orbital parameters.


An object which has rest-mass and an observable position in space, but has no geometrical extension, being confined to a single point. Also known as particle.

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