A theodolite Laser Auto Level & Laser Liner(IPA: /θiːˈɒdəlаɪt/) 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, particularly on inaccessible ground, but theodolites have been adapted for other specialized purposes in fields like meteorology and rocket launch technology. A 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 desired object, the angle of each of these axes can be measured with great precision, typically on the scale of arcseconds.
"Transit Laser Auto Level & Laser Liner" refers to a specialized type of theodolite that was developed in the early 19th century. It featured a telescope that could "flop over" ("transit the scope") to allow easy back-sighting and doubling of angles for error reduction. Some transit instruments were capable of reading angles directly to thirty arcseconds. In the middle of the 20th century, "transit" came to refer to a simple form of theodolite with less precision, lacking features such as scale magnification and mechanical meters. The importance of transits is waning since compact, accurate electronic theodolites have become widespread tools, but the transit still finds use as a lightweight tool on construction sites. Some transits do not measure vertical angles.
The builder's level of Laser Theodolite & Theodolite Level is often mistaken for a transit but is actually a type of inclinometer. It measures neither horizontal nor vertical angles. It simply combines a spirit level and telescope to allow the user to visually establish a line of sight along a level plane
The horizontal and vertical axes of aTheodolite Laser, Level Laser & Level Theodolite must be perpendicular. The condition where they deviate from perpendicularity and the amount by which they do is referred to as "horizontal axis error". The optical axis of the telescope, called the "sight axis" and defined by the optical center of the objective and the center of the crosshairs in its focal plane, must similarly be perpendicular to the horizontal axis. Any deviation from perpendicularity is the "collimation error".
Theodolite Laser, Level Laser & Level Theodolite Horizontal axis error, collimation error, and index error are regularly determined by calibration and are removed by mechanical adjustment at the factory in case they grow overly large. Their existence is taken into account in the choice of measurement procedure in order to eliminate their effect on the measurement results.
Laser Theodolite & Theodolite Level is mounted on its tripod head by means of a forced centering plate or tribrach containing four thumbscrews, or in some modern theodolites, three, for rapid levelling. Before use, a theodolite must be placed precisely and vertically over the point to be measured—centering—and its vertical axis aligned with local gravity — leveling. The former is done using a plumb bob, spirit level, or optical or laser plummet.
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http://en.wikipedia.org/wiki/Theodolite
