BASIC TOOLS OF SURVEYING (P-4)

Total Station

                             A total station or TST (Total Station Theodolite) is an electronic / optical instrument used in modern surveying and building construction. The total station is an electronic theodolite (transit) integrated with an electronic distance mete (EDM) to read slope distances from the instrument to a particular point.

Robotic total station allows the operator to control the instrument from a distance via remote control. This eliminates the need for an assistance staff member as the operator holds the reflector and controls the total station from the observed point.

The Transit and Theodolite:

                             The transit and theodolite are used by the surveyor to measure both horizontal and vertical angles.  While the purpose of the two is similar, as a general rule a theodolite is more accurate than a transit.  However, there is no specific rule as to when one definition ends and the other begins.  Generally, these instruments have a minimum accuracy of one minute of angle and some very precise theodolites will measure angles to an accuracy of one-tenth of a second of angle.  To put these accuracies into perspective, at a distance of one mile, one minute of angle covers about 1.5 feet.  At a distance of one mile, one tenth of a second of angle covers about 0.003 feet.

               Transit                                     Theodolite

The Level:

                             The surveyor uses a level to determine elevations.  Levels fall into three broad categories:  a "dumpy" level, a "Wye" (or 'Y') level, and "automatic" level.  As with all tools of the surveyor, there are various degrees of accuracy within each category of level.         

A "dumpy" level has a telescope with cross hairs permanently mounted in a pair of arms.

A "Wye level has a telescope with cross hairs that is removable from the arms.

An "automatic" level is basically a dumpy level, but it has a built in compensator that automatically adjusts for minor errors in the setup of the instrument.

In conjunction with a level, the surveyor will use a "level rod" to read an elevation up or down from the level of the telescope.  From these observations, a surveyor can determine differences in elevation of different points or transfer an elevation from one location to a distant location.

Wey Level                                Automatic Level