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A theodolite is an instrument used to determine the relative position of points on the earth's surface by measuring the horizontal and vertical angles. Theodolites can be either digital or non-digital types. Digital theodolites are more convenient and accurate as they provide digital readouts instead of reading directly from the traditional graduated circle.
This article explains the parts, working, and features of digital theodolites used in surveying.
Parts of a Digital Theodolite
A digital theodolite consists of a telescope mounted on a base, as shown in Figure-1 below. A sight on the top of the telescope is used to align the target. The target is made clear by using the focusing knob on the instrument. The eyepiece of the telescope is used to find the target. An objective lens is present on the opposite side of the telescope used to sight and magnify the target as required.
The parts of a digital theodolite are mostly similar to a non-digital theodolite, except for the presence of a liquid crystal display (LCD), which shows the reading of the target in focus. The display system also has operating keys for changing the device settings.
Similar to the parts of non-digital theodolite, the leveling is performed using optical plummets or plumb bobs and the spirit or bubble level.
Working of Digital Theodolite
The theodolite is first made to stand vertically above the survey point with the help of a plumb bob or optical plummet. The device is later made in level to the horizon with the help of internal spirit levels. After completing the leveling process, the telescope is used to focus on the target and the respective horizontal and vertical angles are displayed on the screen.
A typical theodolite surveying follows the below procedure:
- Mark the station on the ground using a stake or surveyor’s needle, above which the theodolite is planned to be placed.
- Place the tripod over the station. The height of the tripod is adjusted so that the instrument stays at eye level. The centered hole of the mounting plate must be over the station point.
- Mount the theodolite over the tripod and screw it in place using the mounting knob.
- The height difference between the ground and the instrument is measured. This height is used as a reference for other stations.
- The theodolite is leveled by adjusting the tripod legs and the leveling knobs.
- A plumb bob or vertical plummet can be tied at the bottom of the theodolite to adjust the level. The plummet must stay over the station nail.
- After leveling, through the telescope, aim the crosshairs at the point to be measured. The knobs on the side of the theodolite are used to lock it to keep the target on point.
- The horizontal and vertical angles are read from the LCD screen for the target.
A digital theodolite consists of a telescope that is mounted on a base. A sight on the top of the telescope is used to align the target. The object in focus is made clear by using a focusing knob. The eyepiece of the telescope is used to find the target. An objective lens is present on the opposite side of the telescope used to sight and magnify the target as required. It consists of an LCD, which shows the reading of the target in focus. The display system also has operating keys to work with the display.
Digital theodolites are more convenient because digital readouts can be taken instead of reading directly from the traditional graduated circle. The parts of a digital theodolite are mostly similar to a non-digital theodolite, except for the presence of an LCD, which shows the reading of the target focused.