Usually, when surveying, a point is located relative to another point by means of its polar coordinates. Thus, as well as needing a distance, an angle is needed.
As well as the Theodolite and its tripod, some way of accurately marking the points to be surveyed is required. This can be another tripod with a target placed upon it, or simply a wooden peg with a nail hammered into the top. The theolodite requires a skilled operator, and is generally a one man operation.
Imagine that whilst set up on one point, you wish to measure angles between more than 2 other points. This is simple. Use the same method as above, but include the following:-
Repeat step 3 as many times as you have extra points. Rotate the telescope vertically and read the last bearing again, as in step 4,
Then carry out step 5, but instead of swinging directly back to the RO, sight, read and record for each point in the reverse order to which you sighted them in step 3.
Now the angles between each set of points can be calculated in a similar way to step 6 - for the angle between two points of known bearing, subtract the lower bearing from the higher.
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