Theodolite and surveys

A theodolite is an instrument for measuring both horizontal and vertical angles, as used in triangulation networks. It is a key tool in surveying and engineering work. wikipedia

Starting from a benchmark, a position with known location and elevation, the distance and angles to the unknown point are measured. wikipedia

The theodolite is the standard tool of optical survey. It is a small tripod-mounted high precision telescope with a total system magnification of 15x-60x and an array of dials, knobs, levels, and auxiliary lens systems, with which extremely high precision measurements of horizontal ("azimuth'') and vertical ("altitude'') angles are made. Usable resolution of 15 arc seconds (12 parts per million) is common.

One person works the theodolyte (A), the other is assitant (B). B holds vertically at two vertices a pole that must be at least as high as the theodolite's lens and have a perpendicular bubble level (or use a level held against the pole). The pole must be ruled to correspond to the height of the theodolite lens - be clearly readable through the theodolite's eyepiece. Measure the baseline distance between the pole and the theodlyte using a measuring tape.

Now measure the height

Move the pole, place and level the theodolite over it, and use the theodolite's optical plummet or, in its absence, a dangling weight, to center on the hole. Now do the same again to a new point.

Here is a flash animation explaing how to use the theodlyte for measuring angles. To measure heights just measure off the pole...