Theodolite Survey Tips

theodolite atau theodolit merupakan alat yang paling canggih di antara peralatan yang digunakan dalam survei. Pada dasarnya alat ini berupa sebuah teleskop yang ditempatkan pada suatu dasar berbentuk membulat (piringan) yang dapat diputar-putar mengelilingi sumbu vertikal, sehingga memungkinkan sudut horisontal untuk dibaca. Teleskop tersebut juga dipasang pada piringan kedua dan dapat diputar-putar mengelilingi sumbu horisontal, sehingga memungkinkan sudut vertikal untuk dibaca. Kedua sudut tersebut dapat dibaca dengan tingkat ketelitian sangat tinggi (farrington 1997).

Teleskop pada theodolite atau theodolit dilengkapi dengan garis vertikal, stadia tengah, stadia atas dan bawah, sehingga efektif untuk digunakan dalam tacheometri, sehingga jarak dan tinggi relatif dapat dihitung. Dengan pengukuran sudut yang demikian bagus, maka ketepatan pengukuran yang diperoleh dapat mencapai 1 cm dalam 10 km. Pada saat ini alat survey seperti alat theodolit sudah diperbaiki dengan menambahkan suatu komponen elektronik. Komponen ini akan menembakkan beam ke objek yang direfleksikan kembali ke mesin melalui cermin. Dengan menggunakan komponen alat survey seperti alat theodolit tersebut pengukuran jarak dan tinggi relatif hanya berlangsung beberapa detik saja. Bila komponen tersebut ditempatkan pada bagian atas alat theodolite, maka disebut electronic distance measurers (edm), namun bila merupakan satu unit tersendiri maka disebut automatic level atau theodolite total station (farrington 1997).

survei dengan menggunakan theodolite dilakukan bila situs yang akan dipetakan luas dan atau cukup sulit untuk diukur, dan terutama bila situs tersebut memiliki relief atau perbedaan ketinggian yang besar. Dengan menggunakan automatic level atau theodolite total station ini, keseluruhan kenampakan atau gejala akan dapat dipetakan dengan cepat dan efisien (farrington 1997).

Alat-alat yang diperlukan: sebuah survey theodolite, tripod, levelling stave, buku catatan, pensil, patok berbendera untuk menandai situs.

Cara pembacaan sudut berbeda antara satu tipe alat theodolite dengan tipe yang lain. Tiap alat theodolite mempunyai sebuah skala vernier. Skala ini akan memberikan hasil pembacaan derajat dan menit.

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A theodolit Instrument

A theodolit 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, theodolit particularly on inaccessible ground, but theodolit level 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(lihat terjemahannya di alat survey & alat theodolit). 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" refers to a specialized type of theodolit level 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(alat theodolite or automatic level theodolite) have become widespread tools, but the transit still finds use as a lightweight tool on construction sites. Some transits do not measure vertical angles.

Both axes of a theodolite are equipped with graduated circles that can be read out through magnifying lenses. (r. Anders helped m. Denham discover this technology in the 1864) the vertical circle (which 'transits' about the horizontal axis) should read 90° or 100 grad when the sight axis is horizontal, or 270° (300 grad) when the instrument is in its second position, that is, "turned over" or "plunged". Half of the difference between the two positions is called the "index error".

The horizontal and vertical axes of a theodolite must be perpendicular(lihat di alat survey & alat theodolit untuk terjemahannya). 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".

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 of alat theodolite or automatic level theodolite is taken into account in the choice of measurement procedure in order to eliminate their effect on the measurement results.

A theodolite 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

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