establishing control networks and their subsequent computation leads to an implied rectangular coordi- nate system over the area surveyed. the minor control point in particular can now be used to position the methods of topographic survey and dimensional control will most probably be
(a) by polar coordinates (distance and bearing) using total station : or (B) by GPS using kinematic methods.
Considering method (a) atotal station would be set up over control point whose coording are known as ,a, and back - sighted to another control point , b, whose coordinates are also known .
depending on the software on board the coordinates may be keyed into the total station alternatively. the bearing of the line ,ab, computed from the coordinates, may be keyed in assuming the topographic position of a road is required , the total station would be sighted to a corner cube prism fixed to a detail pole held vertically at ,,p,, the edge of the road as shown in figure 1.7 and 1.8 the field data would comprise the horizontal angle bap,,a,, and the horizontal distance D (figure1.8)
Depending on the software being used the angle a,would be used to copute the bearing ap,, relative to ,ab,, and with the horizontal distance d,,
compute the rectangular coordinates of of p1 in the established coordinate system this process is repeated for the remaining point difining the road sdge and any other topographic data within range of the total station the whole area would be surveyed in this way by occupying pairs of control point situated throughout the area.