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 GPS is somewhat less accurate than traditional precise leveling, but may be similar over long distances.
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 GPS system, astronomic observations are rare as GPS allows adequate positions to be determined over most of the surface of the earth.
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.
"Triangulation is a method of horizontal location favoured in the days before EDM and GPS measurement. It can determine distances, elevations and directions between distant objects. Since the early days of surveying, this was the primary method of determining accurate positions of objects for "topographic maps of large areas. A surveyor first needs to know the horizontal distance between two of the objects, known as the baseline. Then the heights, distances and angular position of other objects can be derived, as long as they are visible from one of the original objects. High-accuracy transits or theodolites were used, and angle measurements repeated for increased accuracy. See also "Triangulation in three dimensions.
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 Congress on Surveying and Mapping. It incorporates elements of the boundary survey, mortgage survey, and topographic survey.
- Control surveying: Control surveys establish reference points to use as starting positions for future surveys. Most other forms of surveying will contain elements of control surveying.
- "Construction surveying
- "Deformation survey: a survey to determine if a structure or object is changing shape or moving. First the positions of points on an object are found. A period of time is allowed to pass and the positions are then re-measured and calculated. Then a comparison between the two sets of positions is made.
- Dimensional control survey: This is a type of survey conducted in or on an non-level surface. Common in the oil and gas industry to replace old or damaged pipes on a like-for-like basis. The advantage of dimensional control survey is that the instrument used to conduct the survey does not need to be level. This is useful in the off-shore industry, as not all platforms are fixed and are thus subject to movement.
- Engineering surveying: topographic, layout, and as-built surveys associated with engineering design. They often need geodetic computations beyond normal civil engineering practice.
- Foundation survey: a survey done to collect the positional data on a foundation that has been poured and is cured. This is done to ensure that the foundation was constructed in the location, and at the elevation, authorized in the plot plan, site plan, or subdivision plan.
- "Hydrographic survey: a survey conducted with the purpose of mapping the shoreline and bed of a body of water. Used for navigation, engineering, or resource management purposes.
- "Leveling: either finds the elevation of a given point or establish a point at a given elevation.
- "LOMA survey: Survey to change base flood line, removing property from a "SFHA special flood hazard area.
- Measured survey : a building survey to produce plans of the building. such a survey may be conducted before renovation works, for commercial purpose, or at end of the construction process.
- "Mining surveying: Mining surveying includes directing the digging of mine shafts and galleries and the calculation of volume of rock. It uses specialised techniques due to the restraints to survey geometry such as vertical shafts and narrow passages.
- Mortgage survey: A mortgage survey or physical survey is a simple survey that delineates land boundaries and building locations. It checks for "encroachment, building setback restrictions and shows nearby flood zones. In many places a mortgage survey is a precondition for a mortgage loan.
- "Photographic control survey: A survey that creates reference marks visible from the air to allow "aerial photographs to be "rectified.
- Stakeout, Layout or Setout: an element of many other surveys where the calculated or proposed position of an object is marked on the ground. This can be temporary or permanent. This is an important component of engineering and cadastral surveying.
- Structural survey: a detailed inspection to report upon the physical condition and structural stability of a building or structure. It highlights any work needed to maintain it in good repair.
- Subdivision: A boundary survey that splits a property into two or more smaller properties.
- Topographic survey: a survey that measures the elevation of points on a particular piece of land, and presents them as "contour lines on a plot.
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
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.
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.
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 Service, "National Park Service, "Army Corps of Engineers, "Bureau of Indian Affairs, "Fish and Wildlife Service, "Bureau of Reclamation, and others. The BLM used to be known as the "General Land Office (GLO).
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.
- "International Federation of Surveyors
- "Prismatic compass (surveying)
- "Surveying in early America
- "Definition". fig.net. Retrieved 2016-02-17.
- Johnson, Anthony, Solving Stonehenge: The New Key to an Ancient Enigma. (Thames & Hudson, 2008) "ISBN 978-0-500-05155-9
- Hong-Sen Yan & Marco Ceccarelli (2009), International Symposium on History of Machines and Mechanisms: Proceedings of HMM 2008, "Springer, p. 107, "ISBN "1-4020-9484-1
- Lewis, M. J. T. (2001-04-23). Surveying Instruments of Greece and Rome. Cambridge University Press. "ISBN "9780521792974. Retrieved 30 August 2012.
- Turner, Gerard L'E. Nineteenth Century Scientific Instruments, Sotheby Publications, 1983, "ISBN 0-85667-170-3
- Sturman, Brian; Wright, Alan. "The History of the Tellurometer" (PDF). International Federation of Surveyors. Retrieved 20 July 2014.
- Cheves, Marc. "Geodimeter-The First Name in EDM". Archived from the original on March 10, 2014. Retrieved 2014-07-20.
- Mahun, Jerry. "Electronic Distance Measurement". Jerrymahun.com. Retrieved 2014-07-20.
- National Cooperative Highway Research Program: Collecting, Processing and Integrating GPS data into GIS, p. 40. Published by Transportation Research Board, 2002 "ISBN 0-309-06916-5 "ISBN 978-0-309-06916-8
- Toni Schenk, Suyoung Seo, Beata Csatho: Accuracy Study of Airborne Laser Scanning Data with Photogrammetry, p. 118 Archived March 25, 2009, at the "Wayback Machine.
- "View DigitalGlobe Imagery Solutions @ Geospatial Forum".
- Ronalds, B.F. (2016). Sir Francis Ronalds: Father of the Electric Telegraph. London: Imperial College Press. "ISBN "978-1-78326-917-4.
- Kahmen, Heribert; Faig, Wolfgang (1988). Surveying. Berlin: de Gruyter. p. 9. "ISBN "3-11-008303-5. Retrieved 2014-08-10.
- BC Punmia. Surveying by BC Punmia. p. 2. Retrieved 9 December 2014h.
- N N Basak. Surveying and Levelling. p. 542. Retrieved 28 July 2016.
- BC Punmia. Surveying by BC Punmia. p. 2. Retrieved 9 December 2014.
- A History of the Rectangular Survey System by C. Albert White, 1983, Pub: Washington, D.C. : U.S. Dept. of the Interior, Bureau of Land Management : For sale by Supt. of Docs., U.S. G.P.O.,
- Richards, D., & Hermansen, K. (1995). Use of extrinsic evidence to aid interpretation of deeds. Journal of Surveying Engineering, (121), 178.
- "The Surveying Handbook". 1995. "doi:10.1007/978-1-4615-2067-2. "ISBN "978-1-4613-5858-9.
- Keay J (2000), The Great Arc: The Dramatic Tale of How "India was Mapped and "Everest was Named, Harper Collins, 182pp, "ISBN 0-00-653123-7.
- Pugh J C (1975), Surveying for Field Scientists, Methuen, 230pp, "ISBN 0-416-07530-4
- Genovese I (2005), Definitions of Surveying and Associated Terms, ACSM, 314pp, "ISBN 0-9765991-0-4.
- Public Land Survey System Foundation (2009) Manual of Surveying Instructions For the Survey of the Public Lands of the United States. www.blmsurveymanual.org
|""||Look up surveying in Wiktionary, the free dictionary.|
|"Library resources about
|""||Wikimedia Commons has media related to Surveying.|
- Géomètres sans Frontières : Association de géometres pour aide au développement. NGO Surveyors without borders (French)
- SurveyorConnect Community forum for Land Surveyors and Geomatics Professionals offering peer-to-peer support, education, networking and tales from the field.
- The National Museum of Surveying The Home of the National Museum of Surveying in Springfield, Illinois
- Land Surveyors United Support Network Global social support network featuring surveyor forums, instructional videos, industry news and support groups based on geolocation.
- Natural Resources Canada – Surveying Good overview of surveying with references to construction surveys, cadastral surveys, photogrammetry surveys, mining surveys, hydrographic surveys, route surveys, control surveys and topographic surveys
- Table of Surveying, 1728 Cyclopaedia
- Surveying & Triangulation The History Of Surveying And Survey Equipment
- NCEES National Council of Examiners for Engineering and Surveying (NCEES)
- NSPS National Society of Professional Surveyors (NSPS)
- Ground Penetrating Radar FAQ Using Ground Penetrating Radar for Land Surveying
|This article needs additional or more specific "categories. (July 2016)|