Total Stations, Theodolites and Transits Information
Theodolites and Transits are used for the accurate measurement of features, orientation and absolute positioning of large scale objects in engineering, construction, mapping, industry, defense and other applications. They are used to establish and mark the position and detailed layout of new structures such as roads or buildings. modern theodolite consists of a movable telescope mounted within two perpendicular axes — the horizontal or trunnion axis, and the vertical axis. When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc. A standard transit is a telescope with cross-hairs for sighting a target. The telescope is attached to scales for measuring the angle of rotation of the telescope (normally relative to north as 0 degrees) and the angle of inclination of the telescope (relative to the horizontal as 0 degrees). An electronic distance measuring device (EDM) measures the distance from the instrument to its target.
Theodolites and Transits are used to perform GPS surveying, engineering surveying, and topographic surveying. GPS surveying uses signals from GPS satellites to determine the location of objects with great accuracy. Engineering surveying involves the preparation of maps and plans for the planning and design of structures. Topographic surveying involves determining the relative locations of observable features on the earth's surface by measuring horizontal distances, differences in elevation and direction.
Theodolites can be mechanical or digital in design. Optical surveying instruments often employ telescopes, which differ in terms of specifications such as erect image, magnification, resolving power in degrees of arc, field of view, minimum focus, and stadia ratio. The internal data storage capacity of a digital surveying instrument can be measured in points. Surveying software functions include data collection in the field, compatibility with data from total stations and data collectors, and import/export to computer aided design (CAD) software.
The International Organization for Standardization (ISO) Technical Committee 172, Subcommittee 6 (geodetic and surveying instruments) maintains standards applicable to surveying instruments. ISO 9849 discusses terminology. ISO 12858 deals with ancillary devices for the following geodetic instruments: Invar leveling staffs, tripods, and tribrachs. ISO 17123 covers field test procedures for surveying instruments.