distance is one of the fundamental measurments in surveying Although frequently measured as spatial distance (sloping distance) in three-dimensional space , usually it is the horizontal component which is required ,
Distance is required in many instance , e,g to give scale to network of control points , to fix the position of topographic detail by offsets or polar coordinates to set out the position of a point in construction work , etc .
The basic method of measuring distance are , at the present time , by taping or by elevtromagnetic ( or electro-optical ) distance measurement , generally designated as EDM . For very rough reconnaissance surveys or approximate estimates pacing may be suitable .
For distances over 5 km , GPS satellite methodes , which can measure the vectors between two points accurate to 1 ppm are usually more suitable .
TAPES :
Taapes come in a variety of lengths and materials . for engineering work the lengths are generally 10 m , 30 m , 50 m and 100 m .
Linen or glass fibre tapes may be used for general use , where precision is not a prime consideration the linen tapes are made from high quality linen , combined with metal fibres to increase their strength .
They are sometimes encased in plastic boxes with recessed handles . These tapes are often graduated in 5-mm intervals only .
More precise versions of the above tapes are made of steel and graduated in millimeters .
For high-accuracy work , steel bands mounted in an open frame are used . They are standardized so that they measure their nominal length at a designated temperature usually 20ً C and at a designated applied tension usually between 50 N to 80 N .
This information is clearly printed on the zero end of the tape .shows a sample of the equipment .
For the most precise work , invar tapes made from 35% nickel and 65 % steel are available . The singular advantage of such tapes is that they have a negligible coefficient of expansion compared with steel ,
and hence temperature variation are not critical , Their disadvantages are that the metal is soft and weak , whilst the price is more than ten times that of steel tapes . An alternative tape , called a lovar tape , is roughly , midway between steel and invar .
Much ancillary equipment is necessary in the actual taping process , e.g
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