surveying indirect leveling ₪ 2. Case where the point is inaccessible

 

We seek to know the altitude of an inaccessible point C knowing only the altitude of close point A which will serve as a reference. If we can measure the horizontal distance AC, we can calculate the height difference from A to C by measuring the angle V read from A to C and the height of the axis of the trunnions ht. The altitude 

 is given by : 

A solution to get the horizontal distance Dh is to create a base AB by adding a second point B, to measure  the horizontal angles CBA and CAB.

This ^makesb it possible to solve the triangle ABC and therefore to calculaate the horizontal distances AC and BC. The altitude of C is then:

We can also calculate the altitude of C twice: :

₪  a firstg time from A

₪  And a second from B and this control the result. 

For this, it is necessary to determine the  ht à chaque station.