Surveying

Question 1

Horizontal controls can be established by various ways such as triangulation and trilateration . These systems consist of a series of joined or overlapping triangles . The principle of triangulation is that the distances are obtained indirectly by measuring the angles in the network . The survey stations are points on the ground which define the vertices triangles forming parts of quadrilateral (fig .1 ) or chains of triangles (fig .2 . Solving trigonometrically , the measured horizontal angles and baseline lengths are used to compute for the position of stations

Trilateration is another

method from the trigonometric proposition that three angles con be computed from three known sides . It is similar to the triangulation system from the geometric figure it employs . However instead of angle measurements , length (distance ) measurements are used in the computations Selection of station locations is an important element to be considered in a triangulation network . The principal factors are (1 ) best fitting for the topography of the area (2 ) survey requirements (3 accessibility and (4 ) permanence . The strength of a triangulation network is easily computed and checked when EDM devices were introduced making practical the measurements with high accuracy under almost all field conditions

In the field , we can execute this survey by occupying station A determining the angle from station B to C and measuring the distance between A and B . Same procedure applies to the second set-up in station B . If stations A and B are not fully inter-visible , the survey procedures cannot be carried out...