SURVEYING or LAND SURVEYING is the technique, profession, and science of determining the terrestrial or three-dimensional position 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 like building corners or the surface location of subsurface features, or other purposes required by government or civil law, such as property sales.
Surveyors work with elements of geometry , trigonometry , regression
analysis , physics , engineering , metrology , programming languages
and the law . They use equipment like total stations , robotic total
* 1 Definitions
* 1.1 ACSM * 1.2 FIG
* 2 History
* 2.1 Ancient surveying * 2.2 Modern surveying * 2.3 20th century * 2.4 21st century
* 3.1 Hardware * 3.2 Software
* 4.5 Reference networks
* 4.5.1 Datum and coordinate systems
* 4.6 Errors and accuracy
* 5 Types of surveys
* 5.1 Plane and geodetic surveying
* 6 The surveying profession
* 7 See also * 8 References * 9 Further reading * 10 External links
The American Congress on Surveying and Mapping (ACSM), defines surveying as _the science and art of making all essential measurements to determine the relative position of points or physical and cultural details above, on, or beneath the surface of the Earth, and to depict them in a usable form, or to establish the position of points or details._
Also per ACSM, the type of surveying known as "land surveying" is _the detailed study or inspection, as by gathering information through observations, measurements in the field, questionnaires, or research of legal instruments, and data analysis in the support of planning, designing, and establishing of property boundaries. It involves the re-establishment of cadastral surveys and land boundaries based on documents of record and historical evidence, as well as certifying surveys (as required by statute or local ordinance) of subdivision plats or maps, registered land surveys, judicial surveys, and space delineation. Land surveying can include associated services such as mapping and related data accumulation, construction layout surveys, precision measurements of length, angle, elevation, area, and volume, as well as horizontal and vertical control surveys, and the analysis and utilization of land survey data._
The International Federation of Surveyors defines the function of surveying as:
A surveyor is a professional person with the academic qualifications and technical expertise to conduct one, or more, of the following activities;
* to determine, measure and represent land, three-dimensional objects, point-fields and trajectories; * to assemble and interpret land and geographically related information, * to use that information for the planning and efficient administration of the land, the sea and any structures thereon; and, * to conduct research into the above practices and to develop them.
A plumb rule from the book Cassells' Carpentry and Joinery
The Romans recognized land surveying as a profession. They established the basic measurements under which the Roman Empire was divided, such as a tax register of conquered lands (300 AD). Roman surveyors were known as _ Gromatici _.
In medieval Europe, beating the bounds maintained the boundaries of a village or parish. This was the practice of gathering a group of residents and walking around the parish or village to establish a communal memory of the boundaries. Young boys were included to ensure the memory lasted as long as possible.
William the Conqueror
_ Table of Surveying, 1728 Cyclopaedia _
Abel Foullon described a plane table in 1551, but it is thought that the instrument was in use earlier as his description is of a developed instrument.
Gunter\'s chain was introduced in 1620 by English mathematician Edmund Gunter . It enabled plots of land to be accurately surveyed and plotted for legal and commercial purposes.
Leonard Digges described a Theodolite that measured horizontal angles in his book _A geometric practice named Pantometria_ (1571). Joshua Habermel (de:Erasmus Habermehl) created a theodolite with a compass and tripod in 1576. Johnathon Sission was the first to incorporate a telescope on a theodolite in 1725.
In the 18th century, modern techniques and instruments for surveying
began to be used.
Willebrord Snellius (a.k.a. Snel van Royen)
introduced the modern systematic use of triangulation . In 1615 he
surveyed the distance from
It was only towards the end of the 18th century that detailed
triangulation network surveys mapped whole countries. In 1784, a team
William Roy 's
Ordnance Survey of Great Britain began the
In the US, the Land Ordinance of 1785 created the Public Land Survey System . It formed the basis for dividing the western territories into sections to allow the sale of land. The PLSS divided states into township grids which were further divided into sections and fractions of sections.
Robert Torrens introduced the
Torrens system in South Australia in
1858. Torrens intended to simplify land transactions and provide
reliable titles via a centralized register of land. The Torrens system
was adopted in several other nations of the English-speaking world.
A German engineer surveying during the
First World War
At the beginning of the century surveyors had improved the older chains and ropes, but still faced the problem of accurate measurement of long distances. Dr Trevor Lloyd Wadley developed the Tellurometer during the 1950s. It measures long distances using two microwave transmitter/receivers. During the late 1950s Geodimeter introduced electronic distance measurement (EDM) equipment. EDM units use a multi frequency phase shift of light waves to find a distance. These instruments saved the need for days or weeks of chain measurement by measuring between points kilometers apart in one go.
Advances in electronics allowed miniaturization of EDM. In the 1970s the first instruments combining angle and distance measurement appeared, becoming known as total stations . Manufacturers added more equipment by degrees, bringing improvements in accuracy and speed of measurement. Major advances include tilt compensators, data recorders, and on-board calculation programs.
The first satellite positioning system was the
The US Air Force launched the first prototype satellites of the
Global Positioning System (GPS) in 1978.
The theodolite , total station , and RTK
Remote sensing and satellite imagery continue to improve and become cheaper, allowing more commonplace use. Prominent new technologies include three-dimensional (3D) scanning and use of lidar for topographical surveys. UAV technology along with photogrammetric image processing is also appearing.
Further information: List of surveying instruments
The main surveying instruments in use around the world are the
theodolite , measuring tape , total station , 3D scanners ,
The theodolite is an instrument for the measurement of angles. It uses two separate _circles_, _protractors_ or _alidades_ to measure angles in the horizontal and the vertical plane. A telescope mounted on trunnions is aligned vertically with the target object. The whole upper section rotates for horizontal alignment. The vertical circle measures the angle that the telescope makes against the vertical, known as the zenith angle. The horizontal circle uses an upper and lower plate. When beginning the survey, the surveyor points the instrument in a known direction (bearing), and clamps the lower plate in place. The instrument can then rotate to measure the bearing to other objects. If no bearing is known or direct angle measurement is wanted, the instrument can be set to zero during the initial sight. It will then read the angle between the initial object, the theodolite itself, and the item that the telescope aligns with.
The gyrotheodolite is a form of theodolite that uses a gyroscope to orient itself in the absence of reference marks. It is used in underground applications.
The total station is a development of the theodolite with an electronic distance measurement device (EDM). A total station can be used for leveling when set to the horizontal plane. Since their introduction, total stations have shifted from optical-mechanical to fully electronic devices.
Modern top-of-the-line total stations no longer need a reflector or
prism to return the light pulses used for distance measurements. They
are fully robotic, and can even e-mail point data to a remote computer
and connect to satellite positioning systems , such as Global
Positioning System . Real time kinematic
Surveyors use ancillary equipment such as tripods and instrument stands; staves and beacons used for sighting purposes; PPE ; vegetation clearing equipment; digging implements for finding survey markers buried over time; hammers for placements of markers in various surfaces and structures; and portable radios for communication over long lines of sight.
Land surveyors, construction professionals and civil engineers using
total station ,
A standard Brunton Geo compass , still used commonly today by geographers, geologists and surveyors for field-based measurements
Surveyors determine the position of objects by measuring angles and
distances. The factors that can affect the accuracy of their
observations are also measured. They then use this data to create
vectors, bearings, coordinates, elevations, areas, volumes, plans and
maps. Measurements are often split into horizontal and vertical
components to simplify calculation.
Example of modern equipment for surveying (Field-Map
Before EDM devices, distances were measured using a variety of means. These included chains with links of a known length such as a Gunter\'s chain , or measuring tapes made of steel or invar . To measure horizontal distances, these chains or tapes were pulled taut to reduce sagging and slack. The distance had to be adjusted for heat expansion. Attempts to hold the measuring instrument level would also be made. When measuring up a slope, the surveyor might have to "break" (break chain) the measurement- use an increment less than the total length of the chain. Perambulators , or measuring wheels, were used to measure longer distances but not to a high level of accuracy. Tacheometry is the science of measuring distances by measuring the angle between two ends of an object with a known size. It was sometimes used before to the invention of EDM where rough ground made chain measurement impractical.
Historically, horizontal angles were measured by using a compass to provide a magnetic bearing or azimuth. Later, more precise scribed discs improved angular resolution. Mounting telescopes with reticles atop the disc allowed more precise sighting (see theodolite ). Levels and calibrated circles allowed measurement of vertical angles. Verniers allowed measurement to a fraction of a degree, such as with a turn-of-the-century transit .
The plane table provided a graphical method of recording and
measuring angles, which reduced the amount of mathematics required. In
By observing the bearing from every vertex in a figure, a surveyor can measure around the figure. The final observation will be between the two points first observed, except with a 180° difference. This is called a _close_. If the first and last bearings are different, this shows the error in the survey, called the _angular misclose_. The surveyor can use this information to prove that the work meets the expected standards.
Main article: Levelling Center for Operational Oceanographic Products and Services staff member conducts tide station leveling in support of the US Army Corp of Engineers in Richmond, Maine.
The simplest method for measuring height is with an altimeter using
air pressure to find height. When more precise measurements are
needed, means like precise levels (also known as differential
leveling) are used. When precise leveling, a series of measurements
between two points are taken using an instrument and a measuring rod.
Differences in height between the measurements are added and
subtracted in a series to get the net difference in elevation between
the two endpoints. With the
Global Positioning System (GPS), elevation
can be measured with satellite receivers. Usually
When using an optical level, the endpoint may be out of the effective range of the instrument. There may be obstructions or large changes of elevation between the endpoints. In these situations, extra setups are needed. _Turning_ is a term used when referring to moving the level to take an elevation shot from a different location. To "turn" the level, one must first take a reading and record the elevation of the point the rod is located on. While the rod is being kept in exactly the same location, the level is moved to a new location where the rod is still visible. A reading is taken from the new location of the level and the height difference is used to find the new elevation of the level gun. This is repeated until the series of measurements is completed. The level must be horizontal to get a valid measurement. Because of this, if the horizontal crosshair of the instrument is lower than the base of the rod, the surveyor will not be able to sight the rod and get a reading. The rod can usually be raised up to 25 feet high, allowing the level to be set much higher than the base of the rod.
The primary way of determining one's position on the earth's surface
when no known positions are nearby is by astronomic observations.
Observations to the sun, moon and stars could all be made using
navigational techniques. Once the instrument's position and bearing to
a star is determined, the bearing can be transferred to a reference
point on the earth. The point can then be used as a base for further
observations. Survey-accurate astronomic positions were difficult to
observe and calculate and so tended to be a base off which many other
measurements were made. Since the advent of the
Main article: Geodetic network A survey using traverse and offset measurements to record the location of the shoreline shown in blue. Black dashed lines are traverse measurements between reference points (black circles). The red lines are offsets measured at right angles to the traverse lines.
Few survey positions are derived from first principles. Instead, most surveys points are measured relative to previous measured points. This forms a reference or _control_ network where each point can be used by a surveyor to determine their own position when beginning a new survey.
Survey points are usually marked on the earth's surface by objects ranging from small nails driven into the ground to large beacons that can be seen from long distances. The surveyors can set up their instruments on this position and measure to nearby objects. Sometimes a tall, distinctive feature such as a steeple or radio aerial has its position calculated as a reference point that angles can be measured against.
_Offsetting_ is an alternate method of determining position of objects, and was often used to measure imprecise features such as riverbanks. The surveyor would mark and measure two known positions on the ground roughly parallel to the feature, and mark out a baseline between them. At regular intervals, a distance was measured at right angles from the first line to the feature. The measurements could then be plotted on a plan or map, and the points at the ends of the offset lines could be joined to show the feature.
_Traversing_ is a common method of surveying smaller areas. The surveyor starts from an old reference mark or known position and places a network of reference marks covering the survey area. They then measure bearings and distances between the reference marks, and to the target features. Most traverses form a loop pattern or link between two prior reference marks so the surveyor can check their measurements.
Datum And Coordinate Systems
Many surveys do not calculate positions on the surface of the earth, but instead measure the relative positions of objects. However, often the surveyed items need to be compared to outside data, such as boundary lines or previous surveys objects. The oldest way of describing a position is via latitude and longitude, and often a height above sea level. As the surveying profession grew it created Cartesian coordinate systems to simplify the mathematics for surveys over small parts of the earth. The simplest coordinate systems assume that the earth is flat and measure from an arbitrary point, known as a 'datum' (singular form of data). The coordinate system allows easy calculation of the distances and direction between objects over small areas. Large areas distort due to the earth's curvature. North is often defined as true north at the datum.
For larger regions, it is necessary to model the shape of the earth using an ellipsoid or a geoid. Many countries have created coordinate-grids customized to lessen error in their area of the earth.
ERRORS AND ACCURACY
A basic tenet of surveying is that no measurement is perfect, and that there will always be a small amount of error. There are three classes of survey errors:
* _Gross errors or blunders:_ Errors made by the surveyor during the survey. Upsetting the instrument, misaiming a target, or writing down a wrong measurement are all gross errors. A large gross error may reduce the accuracy to an unacceptable level. Therefore, surveyors use redundant measurements and independent checks to detect these errors early in the survey. * _Systematic:_ Errors that follow a consistent pattern. Examples include effects of temperature on a chain or EDM measurement, or a poorly adjusted spirit-level causing a tilted instrument or target pole. Systematic errors that have known effects can be compensated or corrected. * _Random:_ Random errors are small unavoidable fluctuations. They are caused by imperfections in measuring equipment, eyesight, and conditions. They can be minimized by redundancy of measurement and avoiding unstable conditions. Random errors tend to cancel each other out, but checks must be made to ensure they are not propagating from one measurement to the next.
Surveyors avoid these errors by calibrating their equipment, using consistent methods, and by good design of their reference network. Repeated measurements can be averaged and any outlier measurements discarded. Independent checks like measuring a point from two or more locations or using two different methods are used. Errors can be detected by comparing the results of the two measurements.
Once the surveyor has calculated the level of the errors in his work, it is adjusted . This is the process of distributing the error between all measurements. Each observation is weighted according to how much of the total error it is likely to have caused and part of that error is allocated to it in a proportional way. The most common methods of adjustment are the Bowditch method, also known as the compass rule, and the Principle of least squares method.
The surveyor must be able to distinguish between accuracy and precision . In the United States, surveyors and civil engineers use units of feet wherein a survey foot breaks down into 10ths and 100ths. Many deed descriptions containing distances are often expressed using these units (125.25 ft). On the subject of accuracy, surveyors are often held to a standard of one one-hundredth of a foot; about 1/8 inch. Calculation and mapping tolerances are much smaller wherein achieving near-perfect closures are desired. Though tolerances will vary from project to project, in the field and day to day usage beyond a 100th of a foot is often impractical.
TYPES OF SURVEYS
Local organisations or regulatory bodies class specializations of surveying in different ways. Broad groups are:
* _As-built survey_: a survey that documents the location of
recently constructed elements of a construction project. As-built
surveys are done for record, completion evaluation and payment
purposes. An as-built survey is also known as a 'works as executed
survey'. As built surveys are often presented in red or redline and
laid over existing plans for comparison with design information.
* _Cadastral or boundary surveying _: a survey that establishes or
re-establishes boundaries of a parcel using a legal description . It
involves the setting or restoration of monuments or markers at the
corners or along the lines of the parcel. These take the form of iron
rods , pipes , or concrete monuments in the ground, or nails set in
concrete or asphalt. The _ALTA/ACSM_ Land Title Survey is a standard
proposed by the
American Land Title Association and the American
PLANE AND GEODETIC SURVEYING
Based on the considerations and true shape of the earth, surveying is broadly classified into two types.
_Plane surveying_ assumes the earth is flat. Curvature and spheroidal shape of the earth is neglected. In this type of surveying all triangles formed by joining survey lines are considered as plane triangles. It is employed for small survey works where errors due to the earth's shape are too small to matter.
In _geodetic surveying_ the curvature of the earth is taken into account while calculating reduced levels, angles, bearings and distances. This type of surveying is usually employed for large survey works. Survey works up to 100 square miles (260 square kilometers ) are treated as plane and beyond that are treated as geodetic. In geodetic surveying necessary corrections are applied to reduced levels, bearings and other observations.
THE SURVEYING PROFESSION
Surveying In North America , and
The basic principles of surveying have changed little over the ages, but the tools used by surveyors have evolved. Engineering, especially civil engineering , often needs surveyors.
Surveyors help determine the placement of roads , railways , reservoirs , dams , pipelines , retaining walls , bridges , and buildings. They establish the boundaries of legal descriptions and political divisions. They also provide advice and data for _geographical information systems _ (GIS) that record land features and boundaries.
Surveyors must have a thorough knowledge of algebra , basic calculus , geometry , and trigonometry . They must also know the laws that deal with surveys, real property , and contracts .
Most jurisdictions recognize three different levels of qualification:
_Survey assistants_ or _chainmen_ are usually unskilled workers who help the surveyor. They place target reflectors, find old reference marks, and mark points on the ground. The term 'chainman' derives from past use of measuring chains . An assistant would move the far end of the chain under the surveyor's direction.
_Survey technicians_ often operate survey instruments, run surveys in the field, do survey calculations, or draft plans. A technician usually has no legal authority and cannot certify his work. Not all technicians are qualified, but qualifications at the certificate or diploma level are available.
_Licensed, registered, or chartered surveyors_ usually hold a degree or higher qualification. They are often required to pass further exams to join a professional association or to gain certifying status. Surveyors are responsible for planning and management of surveys. They have to ensure that their surveys, or surveys performed under their supervision, meet the legal standards. Many principals of surveying firms hold this status.
Not all surveys are carried out by professional surveyors. Depending on the jurisdiction and circumstances, the builders of a structure may set it out themselves. Surveyors often set out the most significant corners of a building. The builders then lay out the rest of the building themselves using simple surveying techniques.
Licensing requirements vary with jurisdiction, and are commonly consistent within national borders. Prospective surveyors usually have to receive a degree in surveying, followed by a detailed examination of their knowledge of surveying law and principles specific to the region they wish to practice in, and undergo a period of on-the-job training or portfolio building before they are awarded a license to practise. Licensed surveyors usually receive a post nominal , which varies depending on where they qualified. The system has replaced older apprenticeship systems.
A licensed land surveyor is generally required to sign and seal all plans. The state dictates the format, showing their name and registration number.
In many jurisdictions, surveyors must mark their registration number on survey monuments when setting boundary corners. Monuments take the form of capped iron rods, concrete monuments, or nails with washers.
Most countries' governments regulate at least some forms of surveying. Their survey agencies establish regulations and standards. Standards control accuracy, surveying credentials, monumentation of boundaries and maintenance of geodetic networks . Many nations devolve this authority to regional entities or states/provinces. Cadastral surveys tend to be the most regulated because of the permanence of the work. Lot boundaries established by cadastral surveys may stand for hundreds of years without modification.
Most jurisdictions also have a form of professional institution representing local surveyors. These institutes often endorse or license potential surveyors, as well as set and enforce ethical standards. The largest institution is the International Federation of Surveyors (Abbreviated FIG, for French : _Fédération Internationale des Géomètres_). They represent the survey industry worldwide.
Main article: Building surveying § Profession
Most English-speaking countries consider building surveying a distinct profession. They have their own professional associations and licensing requirements. Building surveyors focus on investigating the condition of buildings as well as legal compliance work.
Main article: Cadastral surveying
One of the primary roles of the land surveyor is to determine the boundary of real property on the ground. The surveyor must determine where the adjoining landowners wish to put the boundary. The boundary is established in legal documents and plans prepared by attorneys, engineers, and land surveyors. The surveyor then puts monuments on the corners of the new boundary. They might also find or resurvey the corners of the property monumented by prior surveys.
CADASTRAL LAND SURVEYORS are licensed by governments. The cadastral
survey branch of the
Bureau of Land Management (BLM) conducts most
cadastral surveys in the United States. They consult with Forest
National Park Service
In states organized per the Public Land Survey System (PLSS), surveyors must carry out BLM cadastral surveys under that system.
Cadastral surveyors often have to work around changes to the earth that obliterate or damage boundary monuments. When this happens, they must consider evidence that is not recorded on the title deed. This is known as extrinsic evidence. F.V. Hayden 's map of Yellowstone National Park , 1871. His surveys were a significant basis for establishing the park in 1872.
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* Public Land Survey System Foundation (2009) _Manual of Surveying Instructions For the Survey of the Public Lands of the United States_. www.blmsurveymanual.org