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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").
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 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 ...
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 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 ...
Mirrors and lenses are the critical light-bending components of a telescope. Objective: The first lens or curved mirror that collects and focuses the incoming light. ...
The instrument was paid for by the Crown and the King immediately presented it to the Royal Society; for this reason the theodolite is designated as the Royal Society theodolite, or Ramsden RS in short. There is a complete description of this theodolite in the final report of the Anglo-French Survey (1784–1790). [4]