English

A method of accurate positioning; transmissions of an electromagnetic position fixing system are received at known positions ashore and the offsets between absolute known positions and system positions are transmitted to the ship in the vicinity. The offsets are applied to the measurements of the ship's receiver.

In mapping, the difference in unit contraction along the grain structure of the material as compared to the unit contraction across the grain structure; frequently refers to photographic film and papers and to map materials in general.

The bending of the RAYS of RADIANT ENERGY around the edges of an obstacle, or when passing near the edges of an opening, or through a small hole or slit, resulting in the formation of a SPECTRUM, or arrangement by WAVE LENGTH of component WAVES, producing, for visible WAVE LENGTHS, the chromatic SPECTRUM. The bending of a WAVE as it passes an obstruction.

A model representing the terrain surface by a collection of digital data, mainly coordinates in three dimensions, x, y, and z, and a digitally defined method to interpolate arbitrary terrain heights in between the stored values. Not to be confused with digital cartographic model which may also contain digital data representing terrain, but in a form suitable for the drawing of a particular kind of map.

A computer aided device equipped with a digitizing table and a CURSOR for digitally capturing graphical data (pictures, charts), usually based on vector-techniques (as opposed to a SCANNER). The digitizing table consists of a gridded electrical network under the table's surface which allows an automatic computation of the planar x/y coordinates of a cursor's position. Lines are sequentially scanned by moving the cursor along the position and identifying the appropriate symbol on a menu.

An artifi­cial ditch to hold, or control the FLOW of water. An artificial EMBANKMENT to contain or hold back water. In GEOLOGY, a tabular body of IGNEOUS ROCK molded from molten ROCK within a fissure.

A parameter relating the precision of the position (and/or an unknown auxiliary) provided by a positioning system to that of the "observed quantities" directly measured by the system. DOP is a measure of the influence of the geometry of loci on the precision of position fixing. DOP is frequently used with a qualifying term such as geometric (GDOP), horizontal (HDOP), vertical (VDOP) etc. to indicate that DOP is related to all or some unknown quantities.

The vertical angle, at the eye of an observer between the horizontal and the LINE OF SIGHT to the APPARENT HORIZON. Also called dip of the horizon or depression of the horizon. The angle between the horizontal and the LINES OF FORCES of the EARTH's MAGNETIC FIELD at any point. Also called magnetic dip or magnetic inclination.

An instrument for measuring MAGNETIC DIP. It consists essentially of a DIP NEEDLE or MAGNETIC NEEDLE, suspended in such manner as to be free to rotate about a horizontal AXIS. Also called IN­CLINOME­TER, or dipping compass. See also EARTH INDUCTOR.