Resection and intersection
Using these techniques, one can establish the coordinates of a point P, by observations to or from known points. These techniques are useful for obtaining the position of single points, to provide control for setting out or detail survey in better positions than the existing control may be.
This involves sighting in to P from known positions . If the bearings of the rays are used, then using the rays in combinations of two, the coordinates of P are obtained as follows:
it is required to find the coordinates of P, using the bearings α and β to P from known points A and B whose coordinates are EA, NA and EB, NB.
Intersection by angles
Intersection by bearings
Using equations the coordinates of P are computed. It is assumed that P is always to the right of A → B, in the equations. If the observed angles α and β, measured at A and B are used (Figure) the equations become
The above equations are also used in the direct solution of triangulation. The inclusion of an additional ray from C, affords a check on the observations and the computation.