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The term transit theodolite, or transit for short, refers to a type of theodolite where the telescope is short enough to rotate in a full circle on its horizontal axis as well as around its vertical axis. It features a vertical circle which is graduated through the full 360 degrees and a telescope that could "flip over" ("transit the scope").
A schematic representation of a theodolite's axes and circles. A gon = 1/400ᵗʰ of a circle = 0.9° (= 1 gradian), 100 gon (or grads) = 90°. Modern theodolites measure angles in rads (1 rad = the distance of the radius, hence 2π rads circumference).
The initial setting operation includes fixing the theodolite on a tripod, along with approximate levelling and centering over the station mark.For setting up the instrument, the tripod is placed over the station with its legs widely spread so that the centre of the tripod head lies above the station point and its head approximately level (by eye estimation).
The permanent adjustments of theodolites are made to establish fixed relationship between the instrument's fundamental lines. The fundamental lines or axis of a transit theodolite include the following:- Vertical axis; Axis of plate levels; Axis of telescope; Line of collimation; Horizontal axis; Axis of altitude bubble and the vernier should ...
In 1949, the gyro-theodolite – at that time called a "meridian pointer" or "meridian indicator" [2] – was first used by the Clausthal Mining Academy underground. Several years later it was improved with the addition of autocollimation telescopes. In 1960, the Fennel Kassel company produced the first of the KT1 series of gyro-theodolites. [3]
The alidade is the part of a theodolite that rotates around the vertical axis, and that bears the horizontal axis around which the telescope (or visor, in early telescope-less instruments) turns up or down. In a sextant or octant the alidade is the turnable arm carrying a mirror and an index to a graduated circle in a vertical plane. Today it ...
Normal-section azimuth is the angle measured at our viewpoint by a theodolite whose axis is perpendicular to the surface of the spheroid; geodetic azimuth (or geodesic azimuth) is the angle between north and the ellipsoidal geodesic (the shortest path on the surface of the spheroid from our viewpoint to Point 2).
Ramsden made at least one other 3-foot (0.91 m) theodolite of which parts were discovered in Switzerland. [2] After his death his firm was inherited by Mathew Berge who is known to have constructed two more large instruments to Ramsden's design. [ 2 ]