The role and use of theodolite

Theodolites are divided into vernier theodolites, optical theodolites and electronic theodolites according to the different scales and reading methods of the dial. At present, optical theodolites and electronic theodolites are mainly used in my country, and vernier theodolites have long been eliminated.

Theodolite is a measuring instrument designed based on the principle of angle measurement for measuring horizontal and vertical angles. It is divided into optical theodolites and electronic theodolites. Currently the most commonly used one is the electronic theodolite.

The theodolite is the mechanical part of the telescope, which enables the telescope to point in different directions. The theodolite has two mutually perpendicular axes of rotation to adjust the azimuth and horizontal height of the telescope. The theodolite is an angle measuring instrument, which is equipped with a telescope, a horizontal degree disk and a reading index, and a vertical degree disk and a reading index.

The horizontal and vertical dials of optical longitude and latitude are made of glass. There are equally spaced scale lines engraved on the edge of the plane of the dial. The central angle of the circle corresponding to the distance between two adjacent scale lines is called the scale value of the dial, also known as the minimum scale value of the dial. Generally, the accuracy is determined by the size of the scale value, which is divided into:

DJ6: 1° DJ2: 20′ DJ1 (T3): 4′ According to the accuracy from high to low: DJ07, DJ1, DJ2, DJ6, DJ30, etc. (D and J are the first letters of the geodetic and theodolite respectively)

The theodolite is a precision measuring instrument used to measure angles in surveying tasks. It can be used to measure angles, engineering layout, and rough distance measurement. The whole set of instruments consists of two parts: the instrument and the tripod.

Application example (given the coordinates of points A and B, find the coordinates of point C):

The instrument is set up at one of the two known coordinates of A and B (the instrument is set up at point A), and after completing the basic operation of placement and centering, it is aimed at another known point (point B), and then a reading 1 is configured and recorded according to one's needs, and then the reading 2 is read again at point C (unknown point). The difference between reading 2 and reading 1 is the angle value of angle BAC, and then the distances of AC and BC are accurately measured, and the precise coordinates of point C can be calculated by mathematical methods.

On the construction sites of some construction projects, we often see some technicians carrying out surveying with an instrument. The instrument they use is the theodolite. The original invention of the theodolite is closely related to navigation. In the 15th and 16th centuries, some developed countries such as Britain and France needed to draw various maps and nautical charts because of navigation and war. The earliest map drawing used triangulation, which is to find the position of the third point in the distance based on the observation results at two known points. However, due to the lack of suitable instruments, the angle measurement methods are limited and the accuracy is not high, so the topographic map drawn is not accurate. The invention of the theodolite has improved the observation accuracy of the angle, simplified the measurement and calculation process, and provided more accurate data for map drawing. Later, the theodolite was widely used in the measurement of various engineering construction. The theodolite consists of three parts: the base, the degree plate (horizontal degree plate and vertical degree plate) and the sighting part. The base is used to support the entire instrument. The horizontal degree plate is used to measure the horizontal angle. There are telescopes, level tubes, reading devices, etc. on the sighting part.

The theodolite is the main angle measuring instrument in surveying. It consists of a telescope, a horizontal disc, a vertical disc, a level, a base, etc. During measurement, the theodolite is placed on a tripod, the center of the instrument is aligned with the ground survey station with a plumb bob or an optical plummet, the instrument is leveled with a level, the telescope is aimed at the measuring target, and the horizontal and vertical angles are measured with the horizontal disc and vertical disc. According to accuracy, it can be divided into precision theodolites and ordinary theodolites; according to the reading device, it can be divided into optical theodolites and vernier theodolites; according to the axis system structure, it can be divided into re-survey theodolites and direction theodolites. In addition, there are coded disc theodolites that can automatically record the disc readings according to the coded perforations; automatic tracking theodolites that can continuously and automatically aim at aerial targets; gyro theodolites and laser theodolites that use the gyroscopic orientation principle to quickly and independently determine the orientation of ground points; all-purpose theodolites for astronomical observations that have three functions of theodolite, meridian instrument and zenith instrument; photographic theodolites that combine cameras with theodolites for ground photogrammetry, etc.

An instrument for measuring horizontal and vertical angles. It was first developed by British mechanic Sisson around 1730, and was later improved and formally used in British geodetic surveying. In 1904, Germany began to produce glass disk theodolites. With the development of electronic technology, electronic theodolites appeared in the 1960s. On this basis, electronic tachometers were made in the 1970s.

The theodolite is the mechanical part of the telescope that allows the telescope to point in different directions. The theodolite has two mutually perpendicular axes to adjust the azimuth and horizontal height of the telescope. This type of mount has a simple structure and low cost. It is mainly used in conjunction with ground-based telescopes (for geodetic surveying, bird watching, etc.). If it is used to observe celestial bodies, since the diurnal motion direction of celestial bodies is usually not perpendicular or parallel to the horizon, it is necessary to rotate both axes at the same time and change the rotation speed over time to track the celestial body. However, other celestial bodies in the field of view will rotate relative to the target celestial body. Unless a mechanism is added to offset the rotation of the field of view, it is not suitable for long-exposure astronomical photography.

When measuring, place the theodolite on a tripod, use a plumb bob or optical plummet to align the center of the instrument with the ground survey station, use a level theodolite to level the instrument, use a telescope to aim at the measurement target, and use the horizontal and vertical dials to measure the horizontal and vertical angles. According to accuracy, it can be divided into precision theodolites and ordinary theodolites; according to the reading device, it can be divided into optical theodolites and vernier theodolites; according to the axis system structure, it can be divided into re-survey theodolites and directional theodolites. In addition, there are coded dial theodolites that can automatically record dial readings according to coded perforations; automatic tracking theodolites that can continuously and automatically aim at aerial targets; gyro theodolites and laser theodolites that use the gyroscopic orientation principle to quickly and independently determine the orientation of ground points; all-purpose theodolites for astronomical observations that have three functions of theodolite, meridian instrument and zenith instrument; photographic theodolites that combine cameras with theodolites for ground photogrammetry, etc.

Theodolite Model

The model of the theodolite refers to the angle measurement accuracy, and the specification refers to the code: for example, there are several instruments with different accuracy, such as DJ07, DJ1, DJ2, and DJ16. "D', and "J" represent "geodetic measurement" and "theodolite" respectively. The first letter of the Chinese pinyin of "07*, "1", "2*, and "6" represents the number of seconds of error in the direction observation of this type of instrument. Usually, the letter "D" is omitted when writing. J07, J1 and 12 type theodolites are precision theodolites, and Js type theodolites are ordinary theodolites. In construction projects, 12 and Js type optical theodolites are commonly used. DJ-the model code of the theodolite, mainly including DJ05, DJl, DJ2 and other models.