A tribrach is an attachment plate used to attach a surveying instrument, for example a theodolite, total station, GNSS antenna or target to a tripod. A tribrach allows the survey instrument to be repeatedly placed in the same position over a surveying marker point with sub-millimetre precision, by loosening and re-tightening a lock to adjust the instrument base in a horizontal plane.
The device consists of two triangular metal plates connected at their corners by leveling thumbscrews, a bubble level, a locking mechanism and often an optical plummet. The centre of the bottom plate of the tribrach has a 5/8-11 UNC thread bolt hole which is used to attach the tribrach to the tripod. The top plate has three small holes or slots spaced 120˚ apart above leveling thumbscrews, and a locking mechanism which enables a survey instrument or target to be accurately placed on the tribrach and locked in place.
The optical plummet has either a bullseye or cross-hair sight for positioning the instrument over a survey marker or ground control point. The positional accuracy from sighting through an optical plummet depends on the accuracy of the leveling, which must be performed before the final positioning. The older tribrachs required a plumb line to allow them to be positioned vertically over a point and took longer to set up.
Some modern total stations have an integral laser plummet built in.
The process is iterative between horizontal position and top plate level, because they are interactive. The following general process is followed:
If the target over which the instrument is to be placed is roughly at the same elevation as the tripod feet, the preceding technique is applicable. If there is a considerable difference between the elevation of the target and the elevation of the marker and the instrument bottom plate, such as when the target is in a deep hole, or the tripod is on a Bilby tower, the target will appear to move laterally by a large distance in the optical plummet as the tribrach level is adjusted.
Tribrachs are precision instruments and should be checked regularly to ensure they do not become a source of error.
Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is called a land surveyor. These points are usually on the surface of the Earth, and they are often used to establish maps and boundaries for ownership, locations, such as the designed positions of structural components for construction or the surface location of subsurface features, or other purposes required by government or civil law, such as property sales.
A tripod is a portable three-legged frame or stand, used as a platform for supporting the weight and maintaining the stability of some other object. The three-legged design provides good stability against gravitational loads as well as horizontal shear forces, and better leverage for resisting tipping over due to lateral forces can be achieved by spreading the legs away from the vertical centre. Variations with one, two, and four legs are termed monopod, bipod, and quadripod.
A theodolite is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and infrastructure construction, and some specialized applications such as meteorology and rocket launching.
A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Two basic designs exist: tubular and bull's eye . Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or videographic work.
A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscope, to provide measurement references during visual inspections. Today, engraved lines or embedded fibers may be replaced by a digital image superimposed on a screen or eyepiece. Both terms may be used to describe any set of patterns used for aiding visual measurements and calibrations, but in modern use reticle is most commonly used for weapon sights, while graticule is more widely used for non-weapon measuring instruments such as oscilloscope display, astronomic telescopes, microscopes and slides, surveying instruments and other similar devices.
A total station (TS) or total station theodolite (TST) is an electronic/optical instrument used for surveying and building construction. It is an electronic transit theodolite integrated with electronic distance measurement (EDM) to measure both vertical and horizontal angles and the slope distance from the instrument to a particular point, and an on-board computer to collect data and perform triangulation calculations.
Levelling or leveling is a branch of surveying, the object of which is to establish or verify or measure the height of specified points relative to a datum. It is widely used in geodesy and cartography to measure vertical position with respect to a vertical datum, and in construction to measure height differences of construction artifacts.
A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction, or to cause the spatial cross section of the beam to become smaller.
A triangulation station, also known as a trigonometrical point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity. The nomenclature varies regionally: they are generally known as trigonometrical stations or triangulation stations in North America, trig points in the United Kingdom, trig pillars in Ireland, trig stations or trig points in Australia and New Zealand, and trig beacons in South Africa.
The term Jacob's staff is used to refer to several things, also known as cross-staff, a ballastella, a fore-staff, a ballestilla, or a balestilha. In its most basic form, a Jacob's staff is a stick or pole with length markings; most staffs are much more complicated than that, and usually contain a number of measurement and stabilization features. The two most frequent uses are:
A level is an optical instrument used to establish or verify points in the same horizontal plane in a process known as levelling. It is used in conjunction with a levelling staff to establish the relative height or levels of objects or marks. It is widely used in surveying and construction to measure height differences and to transfer, measure, and set heights of known objects or marks.
A plumb bob, plumb bob level, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical direction as a reference line, or plumb-line. It is a precursor to the spirit level and used to establish a vertical datum. It is typically made of stone, wood, or lead, but can also be made of other metals. If it is used for decoration, it may be made of bone or ivory.
Tacheometry is a system of rapid surveying, by which the horizontal and vertical positions of points on the earth's surface relative to one another are determined without using a chain or tape, or a separate levelling instrument. Instead of the pole normally employed to mark a point, a staff similar to a level staff is used. This is marked with heights from the base or foot, and is graduated according to the form of tacheometer in use.
A plane table is a device used in surveying site mapping, exploration mapping, coastal navigation mapping, and related disciplines to provide a solid and level surface on which to make field drawings, charts and maps. The early use of the name plain table reflected its simplicity and plainness rather than its flatness. "Plane" refers to the table being both flat and levelled (horizontal).
A surveyor's tripod is a device used to support any one of a number of surveying instruments, such as theodolites, total stations, levels or transits.
A tripod head is the part of a tripod system that attaches the supported device to the tripod legs, and allows the orientation of the device to be manipulated or locked down. Modular or stand-alone tripod heads can be used on a wide range of tripods, allowing the user to choose which type of head best suits their needs. Integrated heads are built directly onto the tripod legs, reducing the cost of the tripod system.
Survey Camp is an army tradition that was discontinued in the later part of twentieth century but was reinstated in 2002 across the universities of the world with a whole new structure. It is the civil engineering training course for two weeks usually after completion four semesters of bachelor of technology that consists of 8 days working in the field and 6 days of map preparation in the computer lab. Experts say that survey camp provides necessary foundation for civil engineers. Each day in the course there are at least 8 hours of working in the field. Students are divided into groups and they get out with practising surveyors and use their equipment out in the field. A camp incharge teacher appoints group leaders for each group; the leaders are responsible for all the works of his particular group and the equipment. In the computer lab, students learn applications such as AutoCAD and Carlson Survey. The students use these programs to take data collected from the field to develop topographic maps of the particular area. The basic aim of the survey camp is to know various works carried out in the industrial field by surveying, which includes determining the topography of particular area with the help of survey work, map study and reconnaissance work. The methods used for surveying are traversing, levelling and contouring
Temporary adjustments are a set of operations which are performed on a theodolite to make it ready for taking observations. These include its initial setting up on a tripod or other stand, centering, levelling up and focusing of eyepiece.
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:-
A clamp holder or clamp fastener is a piece of laboratory apparatus that is used to secure laboratory clamps, such as extension-type utility clamps, or other attachments to a retort stand or lab frame. The material can be made up of brass, cast iron, stainless steel, aluminium or nickel-plated zinc.