Glossary

Popular terms used throughout this website

 


TACHEOMETER (Tachymeter)

Surveying instrument designed for use in the rapid determination of distance, direction, and difference of elevation from a single observation, using a short base which may be an intergraph part of the instrument.

TERRAIN CORRECTED

These products use precision corrected processing, and also incorporate digital terrain models (DTMs) into the correction process. Elevation models allow terrain relief distortions (from mountains, hills and valleys) to be removed on a pixel by pixel basis. Terrain correction is recommended for all images where relief differences exceed 500 feet.

TIDE

Periodic rise and fall of the water resulting from gravitational interactions between the Sun, Moon, and Earth. The vertical component of the particulate motion of a tidal wave. Although the accompanying horizontal movement of the water is part of the same phenomenon, it is preferable to designate this motion as tidal current. 

TOPOGRAPHY

Configuration (relief) of the land surface; the graphic delineation or portrayal of that configuration in map form, as by contour lines; in oceanography the term is applied to a surface such as the sea bottom or surface of given characteristics within the water mass. 

TRANSIT

Precision surveying instrument; a theodolite in which the telescope can be reversed in direction by rotation about its horizontal axis. 

TRAVERSE

Sequence of lengths and directions of lines connecting a series of stations, obtained from field measurements, and used in determining positions of the stations.

TRIANGULATION

Method of extending horizontal position on the surface of the Earth by measuring the angles of triangles and the included sides of selected triangles. 

TRILATERATION

Method of surveying wherein the lengths of the triangle sides are measured, usually by electronic methods, and the angles are computed from the measured lengths. Compare with triangulation.

UTM

Universal Transverse Mercator projection. A global map projection especially useful for navigation because it preserves angles and compass headings. Area and distance distortions are small.

ZENITH TELESCOPE

Instrument for observing starts near the zenith (a point on the celestial sphere directly above the observer's position).