Tacheometry

Tacheometry:

A system of rapid surveying, by which the positions, both horizontal and vertical, of points on the earth's surface relatively to one another are determined without using a chain or tape or a separate levelling instrument. The ordinary methods of surveying with a theodolite, chain, and levelling instrument (see Surveying) are fairly satisfactory when the ground is pretty clear of obstructions and not very precipitous, but it becomes extremely cumbrous when the ground is much covered with bush, or broken up by ravines. Chain measurements are then both slow and liable to considerable error; the levelling, too, is carried on at great disadvantage in point of speed, though without serious loss of accuracy. These difficulties led to the introduction of tacheometry, in which, instead of the pole formerly employed to mark a point, a staff similar to a level staff is used. This is marked with heights from the foot, and is graduated according to the form of tacheometer in use. The azimuth angle is determined as formerly. The horizontal distance is 1 This mosque is popularly attributed to Ghazan Khan (end of 13th century).

Tacheometry is used for

  • Preparation of topographic map where both horizontal and vertical distances are required to be measured; 
  • survey work in difficult terrain where direct methods of measurements are inconvenient; 
  • reconnaissance survey for highways and railways etc;
  • establishment of secondary control points.

     

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