The art of surveying involves the determination of an unknown position from angular and distance measurements taken from one or more reference positions. A surveying device that is frequently used to acquire such measurements is a total station. In operation, the user generally aligns the total station at a target held by a second user. With a conventional total station, the pointing ("alignment") process is achieved optically by the user's visually locating the target through a viewfinder on the total station.
Early total stations required at least two people to acquire a set of measurements, i.e., one person to place the target and another person to sight the target from the total station. However, it is often desirable to reduce the number of people required to operate the surveying equipment. Consequently, robotic total stations have been developed to assist in locating a target. A robotic total station eliminates the need for a user at the location of the total station. Instead, the single user is at the target and sights the total station visually from the target. Upon visually locating the total station, the user initiates an angular scanning sequence at the total station to obtain more precise angular and distance measurements. The robotic total station then automatically aligns itself with the target. Servo motors in the total station cause the total station to be rotated towards the target. Once the total station is aligned with the reflective target, the angle and distance measurements can be taken. Examples of robotic surveying systems include the Geodimeter System 600 manufactured by Geotronics AB of Sweden, and the TPS-System 1000 total station manufactured by Leica of Switzerland. One problem associated with many robotic total stations is that they tend to have difficulty locating the target. Consequently, with many robotic total stations, the user at the target frequently must return to the total station to make fine tuning adjustments.
Another type of surveying device which reduces the number of required operators is a reflectorless system. Reflectorless systems do not require a second user at the target. These systems are particularly useful when the target is relatively inaccessible. However, reflectorless total stations still require the user to remain at the total station to sight the target.
Hence, what is need is a total station based surveying system which not only can be operated by a single user, but also provides the user with greater freedom of movement, such that the user is not confined to the immediate vicinity of the target or the total station.