The position of the check point P on the dam is determined by a
separate intersection from stations I, II and III.
It is customary to observe at the forward reference stations one
or two and sometimes three long sights towards a remote point in
order to secure the orientation of the direction to P. The remote
points are not coordinated. These special directions are included in
the observations of the tri angulation of the reference stations and
are oriented with the orientations calculated in the adjustment.
At the first forward reference station we get
«I.» Oi
whence
Qfi.i Qai.i Q01.
Also is
Q<Pu.k @°n> etc.
The bearings being given, the direction can now be orient
ed by a new independent set of observations a*. When the weight
coefficients of the orientations Oj, 0\\ and Ojii are expressed in
243
Figure 4
