English

A method of TRIANGULATION in which simultaneous OBSERVA­TIONS are made on parachute flares. This method is used for extending TRIANGULATI­ON over lines too long to be observed by ordinary methods.

In hydrographic SURVEYING, a TRIANGULATION that may be carried out by means of anchored BUOYS when surveying at such a distance from the LAND that the SIGNALS on the SHORE cannot be di­rectly used for locating the SOUNDINGS. Floating trian­gulation can be either connected to and extended from the STATIONS of a shore triangulation or of a fully floating type in which case the POSITIONS of the BUOYS are obtained by means of OBSERVATIONS and measu­re­ments taken at sea. BUOYS are anchored in such a position as to provide a framework for surveying the area.

A method of TRIANGULATION involving simultaneous OBSERVATIONS from three shore STATIONS on a target carried by a ship offshore of the middle STATION. The middle STATION must be visible from each of the two end STATIONS.

The classifying of TRIAN­GULA­TIONS into first-order, second-order, and third-order triangulation, according to the ERROR OF CLOSURE OF TRIANGLES. In first-order work, the average closure is not in excess of 1 SECOND; in second order work, it does not exceed 3 SECONDS; and in third-order work, it does not exceed 5 SECONDS. For the basic first-order work, the computed length through the NETWORK must agree with the measured BASE within 1 part in 50 000, as a minimum, and average about 1 in 75 000, or bet­ter.

ARCS OF TRIANGULATION, sometimes with lines of TRAVERSE, connected together to form a system of loops or circuits extending over an area. Sometimes called tie net when used to tie small ISLANDS together. Also called traverse net or survey net.

A TRIANGULATION SIGNAL consist­ing of two separate struc­tures, independent of one another an inner structure which supports the THEODO­LITE and sometimes the TARGET or SIGNAL LAMP, and an outer structure which supports the observer and his assist­ants and sometimes the TARGET or SIGNAL LAMP. Triangu­lation towers are used to elevate the LINE OF SIGHT above trees, topographic features, and other obstacles that might interfere with the OBSERVATIONS. See BILBY STEEL TOWER.

A demount­able, three-armed plate which is attached to an instrument stand or survey tower and on which the bottoms of the FOOTSCREWS of the instru­ment rest in milled grooves.

A 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.

The way in which a ship floats on the water, in relation to her fore-and-aft line, whether on an even keel or down by the bow or by the stern.