THEODOLI THEO DOLITE TE SURVEYING SURVEY ING
An optical theodolite, manufactured in the Soviet Union in 1958 and used for topographic surveying A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying for surveying applications, and have been adapted for specialized purposes in fields like meteorology and rocket launch technology. technology. A modern theodolite consists of a movable telescope mounted within two perpendicular axes — the horizontal or trunnion or trunnion axis, and the vertical axis. When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc. arc. Transit refers to a specialized type of theodolite developed in the early 19th century. It featured a telescope that could "flip 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 seconds. 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 micrometers. Although precise electronic theodolites have become widespread tools, the transit still finds use as a lightweight tool on construction sites. Some transits do not measure vertical angles. The builder's The builder's level is often mistaken for a transit, but it measures neither horizontal nor vertical angles. It uses a spirit level to set a telescope level to define a line of sight along a level plane. Concept Conc ept of opera o peration tion :
The axes and circles of a theodolite Both axes of a theodolite are equipped with graduated circles that can be read through magnifying lenses. (R. Anders helped M. Denham discover this technology in 1864) The vertical circle which 'transits' about the horizontal axis should read 90° 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".
Diagram of an Optical Theodolite The horizontal and vertical axes of a theodolite must be perpendicular, if not then a "horizontal axis error" exists. This can be tested by aligning the tubular spirit bubble parallel to a line between two footscrews and setting the bubble central. A horizontal axis error exists if the bubble runs off central when the tubular spirit bubble is reversed (turned through 180°). To adjust, remove half the amount the bubble has run off using the adjusting screw, then relevel, test and refine the adjustment. The optical axis of the telescope, called the "sight axis", defined by the optical center of the objective lens and the center of the crosshairs in its focal plane, must also be perpendicular to the horizontal axis. If not, then a "collimation error" exists. Index error, horizontal axis error and collimation error are regularly determined by calibration and are removed by mechanical adjustment. Their existence 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 modern theodolites, three for rapid levelling. Before use, a theodolite must be precisely placed vertical above the point to be measured
using a plumb bob, optical plummet or laser plummet. The instrument is then set level using levelling footscrews and circular and more precise tubular spirit bubbles. Operation in surveying:
U.S. National Geodetic Survey technicians observing with a 0.2 arcsecond resolution Wild T-3 theodolite mounted on an observing stand. Photo was taken during an Arctic field party (circa 1950). Triangulation, as invented by Gemma Frisius around 1533, consists of making such direction plots of the surrounding landscape from two separate standpoints. The two graphing papers are superimposed, providing a scale model of the landscape, or rather the targets in it. The true scale can be obtained by measuring one distance both in the real terrain and in the graphical representation. Modern triangulation as, e.g., practiced by Snellius, is the same procedure executed by numerical means. Photogrammetric block adjustment of stereo pairs of aerial photographs is a modern, three-dimensional variant. In the late 1780s Jesse Ramsden, a Yorkshireman from Halifax, England who had developed the dividing engine for dividing angular scales accurately to within a second of arc, was commissioned to build a new instrument for the British Ordnance Survey. The Ramsden theodolite was used over the next few years to map the whole of southern Britain by triangulation. In network measurement, the use of forced centering speeds up operations while maintaining the highest precision. The theodolite or the target can be rapidly removed from, or socketed into, the forced centering plate with sub-mm precision. Nowadays GPS antennas used for geodetic positioning use a similar mounting system. The height of the reference point of the theodolite—or the target—above the groundbenchmark must be measured precisely. The American transit gained popularity during the 19th century with American railroad engineers pushing west. The transit replaced the railroad compass, sextant and octant and was distinguished by having a telescope shorter than the base arms, allowing the telescope to be vertically rotated past straight down. The transit had the ability to 'flip' over
on its vertical circle and easily show the exact 180 degree sight to the user. This facilitated the viewing of long straight lines, such as when surveying the American West. Previously the user rotated the telescope on its horizontal circle to 180 and had to carefully check the angle when turning 180 degree turns. Modern theodolites :
Modern theodolite Nikon DTM-520 In today's theodolites, the reading out of the horizontal and vertical circles is usually done electronically. The readout is done by a rotary encoder , which can be absolute, e.g. using Gray codes, or incremental, using equidistant light and dark radial bands. In the latter case the circles spin rapidly, reducing angle measurement to electronic measurement of time differences. Additionally, lately CCD sensors have been added to the focal plane of the telescope allowing both auto-targeting and the automated measurement of residual target offset. All this is implemented in embedded software. Also, many modern theodolites, costing up to $10,000 apiece, are equipped with integrated electro-optical distance measuring devices, generallyinfrared based, allowing the
measurement in one go of complete three-dimensional vectors — albeit in instrument-defined polar co-ordinates, which can then be transformed to a pre-existing co-ordinate system in the area by means of a sufficient number of control points. This technique is called a resection solution or free station position surveying and is widely used in mapping surveying. The instruments, "intelligent" theodolites called self-registering tacheometers or "total stations", perform the necessary operations, saving data into internal registering units, or into external data storage devices. Typically, ruggedized laptops or PDAs are used as data collectors for this purpose. Gyrotheodolites :
A gyrotheodolite is used when the north-south reference bearing of the meridian is required in the absence of astronomical star sights. This mainly occurs in the underground mining industry and in tunnel engineering. For example, where a conduit must pass under a river, a vertical shaft on each side of the river might be connected by a horizontal tunnel. A gyrotheodolite can be operated at the surface and then again at the foot of the shafts to identify the directions needed to tunnel between the base of the two shafts. Unlike an artificial horizon or inertial navigation system, a gyrotheodolite cannot be relocated while it is operating. It must be restarted again at each site. The gyrotheodolite comprises a normal theodolite with an attachment that contains a gyroscope mounted so as to sense rotation of the Earth and from that the alignment of the meridian. The meridian is the plane that contains both the axis of the Earth’s rotation and the observer. The intersection of the meridian plane with the horizontal contains the true northsouth geographic reference bearing required. The gyrotheodolite is usually referred to as being able to determine or find true north. A gyrotheodolite will function at the equator and in both the northern and southern hemispheres. The meridian is undefined at the geographic poles. A gyrotheodolite cannot be used at the poles where the Earth’s axis is precisely perpendicular to the horizontal axis of the spinner, indeed it is not normally used within about 15 degrees of the pole because the eastwest component of the Earth’s rotation is insufficient to obtain reliable results. When available, astronomical star sights are able to give the meridian bearing to better than one hundred times the accuracy of the gyrotheodolite. Where this extra precision is not required, the gyrotheodolite is able to produce a result quickly without the need for night observations.
Construction of theodolite:
The theodolite consists of a telescope pivoted around horizontal and vertical axes so that it can measure both horizontal and vertical angles. Today's theodolites are usually equipped with integrated electro-optical distance measuring devices, allowing the measurement in one go of complete three-dimensional vectors -- albeit in instrument-defined polar co-ordinates -- which can then be transformed to a pre-existing co-ordinate system in the area by means of a sufficient number of control points. The upper plate PP is bored centrally to receive a parallel or conical pillar which supports the lower circle of the theodolite or the arm of the level which carries the telescope. In the theodolite the edge of the piate is beveled and divided into 360 or 400 degrees, and to half degrees, or to 20 minutes or 10 minutes, according to the size of the instrument. Surveying Instructions with NBMG's EDM Theodolite Level the theodolite by first adjusting the knurled leveling screw wheels so bull's-eye level is centered. Extend rod so prism center is within 1 cm of its objective height, with rod end resting on ground and in vertical orientation (check bull's-eye level on rod). At the theodolite, the surveyor sights on the prism, first with the sight atop the telescope, then through the telescope. Different definitions of theodolite :
An optical instrument consisting of a small mounted telescope rotatable in horizontal and vertical planes, used to measure angles in surveying, meteorology, and navigation. The theodolite hit a jutting cliff-ledge and exploded like a shell; the books, inkstands, paint boxes, compasses, and rulers showed for a few seconds like a swarm of bees. A theodolite is mounted on a tripod by means of a forced centering plate or tribrach, containing three thumbscrews for rapid leveling.
THEODOLITE calibrated optical instrument used to determine relative position in surveying, navigation, and meteorology. It is similar in construction to a surveyor's transit, consisting of a telescope fitted with a spirit level and mounted on a tripod so that it is free to rotate about its vertical and horizontal axes. Though for sketch maps the compass or graphic techniques are acceptable for measuring angles, only the theodolite can assure the accuracy required in the framework needed for precise mapping. Theodolite Survey in surveying theory and practice:
To verify the reliability of the Survey of some map, we decided to test the angular distances between monuments using a theodolite. a tall multi-storied building was selected as the base of the theodolite readings. The roof offers a good view of all the main monuments. The theodolite was calibrated and aligned to magnetic north (MN) with a compass and positioned on the south-east corner of the building. Readings were taken in clockwise order from MN, starting with site no. 1. The angular difference between a) two monuments and b) the gross offset from MN was measured and recorded. Due to obstruction by a water tank of the field of view between angles 240° and 350° along the Western horizon, the theodolite was repositioned on the NW corner of the building, reset and re-calibrated with the standard reference and the NS baseline. Due to these adjustments, both theodolite positions can be taken as one, called TP. Interestingly, no monuments were found in line with magnetic north or south, such that the north-south is not emphasised. In contrast, the east-west line is prominently represented in both the terrestrial and celestial schemes. To us, this suggests that the east-west line is the more important basis of calculation in astronomy. Explanation about Total Station and Theodolite:
Electronics has allowed to automate and angular measurements. The electronic theodolite represents the device which will transform the angular sizes which have been written down in the form of system of opaque strokes or code paths on a glass disk to electric signals. The disk is appeared through by a light beam; at turn of a theodolite on a
photodetector the signal in a binary code which after decoding is deduced on a board in a digital kind is created. Association of an electronic theodolite, small-sized phase tool and a microcomputer in a uniform design has allowed creating the electronic tacheometer-device, allowing carrying out both angular, and linear measurements with their processing in field conditions. In the foreign literature such devices have received name Total Station (universal station). Their accuracy reaches 0,5 angular seconds and 2 millimeters + 2 mm/km, and range of action - up to 5 kilometers. Introduction of laser techniques in a geodesy has led, in particular, to development of a witty method of leveling by "laser plane " (systems Laserplane). The bright red beam of vertically located laser falls on the rotating prism creating development of a beam in a horizontal plane. It allows to sight on a light spot on lath, put in any direction of the laser. Such way does not give high accuracy, but differs on speed and ensures the functioning on unlimited number lath that is convenient for many works on high-altitude shooting. For exact measurements the digital level working on coded is designed. The code bears the information on height of any place concerning its "zero". The image will be transformed to an electric signal, and at work on two lath excess between points of their installation is automatically defined. The laser beam represents and it is almost ideal a direct basic line in space concerning which it is possible to make measurements at exact installation of equipment, civil work and so forth. For last twenty years there was a new quantum leap which can be named the second revolution in a geodesy. There were the global satellite systems which have cardinally changed a situation in a geodesy and navigation. They allow at once, without any preliminary measurements, to define coordinates of any points on a surface of the Earth and to find distance between them with high accuracy. Similar systems now two: system GPS developed in the USA (Global Positioning System - global system of definition of a site) and domestic system GLONASS (GLOBAL NAVIGATING Satellite System). Both GPS, and GLONASS are constructed, in general, by the same principle though differ in some details.
The space complex represents system from twenty four satellites placed: in GPS - in six orbital planes developed through 60 on a longitude; in system GLONASS - in three planes through 120 at height of the order of 20 thousand kilometers. It allows observing constantly in any point of globe not less than four satellites of each system. On all satellites there are standards of frequency with long-term stability of the order 10-12 - 10-13. Satellites radiate radiowaves on two frequencies (with lengths of waves of the order of 20 centimeters) which "bear” the complex coded signals. The ground complex of system defines coordinates of satellites and transfers them aboard where they are pawned in a signal sent to the Earth, synchronizes satellite "hours" and verifies them with a ground basic time scale. For this purpose at the central station there is a hydrogen standard of frequency with stability 10-14 that corresponds to leaving for 0,3 seconds for one million years. Signals from satellites accept and the equipment in item of measurement processes. Receivers can work in two modes which have received the name of code and phase measurements. Code measurements name also absolute as at once define coordinates of item in geocentrically to system of coordinates. It is done as follows. The radiowaves radiated from the satellite, are modulated on a phase so-called rangemeter by a code, and the same code is developed in the receiver. (two codes - "rough", accessible to everything, and "exact" are stipulated, access to which should be authorized). By comparison of these two code signals define time of distribution of a signal from the satellite up to the receiver in view of a difference of indications of their hours concerning basic time. If simultaneously to measure distances up to four satellites, the system from four equations with four unknown - three coordinates and a difference in time which decision find required coordinates will turn out. The mode of code measurements gives "navigating" accuracy - the order of several tens meters. That it to rise, use two receivers. One establish on item with known coordinates, define in it differences of the measured and calculated ("reference") sizes and transfer them on mobile the receiver for correction of measurements. Such way reduces a mistake to size up to one meter. To the geodetic purposes apply much more exact mode of phase measurements at which define not time of distribution of a signal from the satellite up to the receiver, and shift of a phase of the bearing frequency radiated by the satellite. Carry out them with two carried
receivers and define differences of their coordinates on which it is possible to calculate distance between receivers to within millimeters. And if one of them to place in a point with known coordinates that is usual and it is done, it is possible to receive easily and absolute coordinates of the second receiver at a centrimetric level of accuracy. The primary goal here, as well as in ground phase range finders, is exact definition of an integer of lengths of the waves which have "kept within" on a line the satellite - the receiver or GPS Total Station. This that number about which it was spoken above, but in this case it is much more and to define of it much more difficultly. As the distance up to the satellite equally approximately to 20 thousand kilometers, and length of a wave - about 20 centimeters, number of lengths of waves N turns out the order of one million; to measure this it is necessary absolutely precisely: the mistake on unit will give a deviation on range on 20 centimeters. Some ways of the decision of this problem are now developed, but with it failures in work of system more often are connected. By present time in the different countries many types of GPS Total Station differing by the opportunities are developed. As a matter of fact, the majority of geodetic problems can be solved at use of two basic measuring means: global satellite system and Total Station. Theodolite Setup:
If the theodolite is to be taken from a cool environment to a warm one (especially in humid conditions) allow the theodolite to warm up inside its case where it will not be subject to condensation. Remove the theodolite from its case and loosen the lower clamp so that the leveling plate and leveling head can be rotated independently of the centers. If the theodolite is in use for a long period of time it may require re-leveling periodically due to temperature effects on the tripod and theodolite base. Theodolites functionality:
There are Balloon Observation Theodolites. Pibals and theodolites have a important history in meteorology. A pilot weather balloon (Pibal) theodolite is a device that is similar to a surveyor's transit.
Unlike the surveyor's transit a pibal theodolite utilizes a "bent axis telescope". There is 10sec Digital Theodolite. The Diagonal Eyepiece is for use in areas where large buildings or obstacles prevent an ideal working distance between the Theodolite and target object. With the eyepiece, any target can be measured as long as the distance is at least 4-1/4' (1.3m) between the instrument and target. The Solar Filter is used on the Theodolite to prevent glare under bright sunlit conditions, or when the sun must be sighted to determine position. The theodolite's 22-power non-inverting telescope has two focusing adjustments; one for the precision reticule focus and another for focusing the target. The teak tripod contains a second round spirit level and the height is adjustable to a maximum height of 5 feet, 9 1/2 inches (177 cm) with a maximum eye height of 5 1/2 feet (168 cm). Theodolites in land surveying:
The high-quality optics, the exact and reliable mechanics, well thought over ergonomics and absolute security from external influences are supplemented in modern theodolites with the built in microprocessor and laser techniques. As a result - theodolites gives new consumer qualities of the equipment (GPS total station), and, as consequence, - theodolites gives essential increase of labour productivity of geodesists, topographers and builders.
Feature of modern theodolites as land surveying instrument is: • Opportunity of equipment by the laser index built in a telescope; • Theodolites built in the electronic equaliser; • Ports for view the result of measurements; • Feed from several batteries; • For reading on horizontal and vertical circles could be used an optical micrometer; • Opportunity of aim at by one hand, • Installation the nozzles on theodolites do not demand special adapters;
• Dustproof and water-proof design of theodolites allows to carry out measurements under adverse conditions; • Bilateral system of reading on circles; • Automatic equalizer excludes mistakes in measured corners for an inclination of the tool; • Two viewfinders from both parties of a telescope allow quickly aim at. Theodolites technology validation:
Some measurement was performed using two theodolites. Step 1.
One theodolite was aligned with the surfaces of the cube and used as a transfer standard to determine the angular displacements of the second one. Step 2.
The second theodolites was equipped with a cross-hair target at the focal point of a lens simulating a source at infinity. Step 3.
When re-imaged by the lenses of the LAC, an image of the crosshair was formed on each of the focal planes. The image of the crosshair was ~20 pixels across, allowing the center of the crosshair to be located to ~0.1 pixel. The image of the crosshair was translated along the nominal along-track direction of each focal plane by rotating the theodolites source. Explanation Position measurements were made at several locations for several rows of each array. In this way, the roll and yaw angles of each array were determined to approximately 40-microradian accuracy (0.1 pixels). Direction of using This information was used to map the angular position of each pixel for use in geolocating the on-orbit image data.
