Land Planning and Surveying
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Wikipedia-Article "Surveying"
- For the American space program, see Surveyor program
Surveying is the art and science of accurately determining the position of points and the distances between them. These points are usually, but not exclusively, associated with positions on the surface of the Earth, and are often used to establish land boundaries for ownership or governmental purposes.
In order to accomplish their objective, surveyors use elements of engineering, physics, mathematics and law.
Surveying has been an essential element in the development of the human environment since the beginning of recorded history and it is a requirement in the planning and execution of nearly every form of construction. Its most familiar modern uses are in the fields of transport, building and construction, communications, mapping, and the definition of legal boundaries for land ownership.
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Method
Historically, distances were measured using a variety of means, such as chains with links of a known length, for instance a Gunter's Chain (see Edmund Gunter), or measuring tapes made of steel or invar. In order to measure horizontal distances, these chains or tapes would be pulled taut, to reduce sagging and slack. Additionally, attempts to hold the measuring instrument level would be made. In instances of measuring up a slope, the surveyor might have to "break" the measurment- that is, raise the rear part of the tape upward, plumb from where the last measurement ended.
Horizontal angles were historically measured using compasses, which would provide a magnetic bearing, from which deflections could be measured. This type of instrument was later improved upon, through more carefully scribed discs, providing better angular resolution, as well as through mounting telescopes with reticles for more precise sighting atop the disc. Additionally, levels and calibrated circles allowing measurement of vertical angles were added, along with verniers for measurement down to a fraction of a degree- such as a turn-of-the-century Transit (surveying).
The simplest method for measuring height is with an altimeter, which is basically a barometer—using air pressure as an indication of height. But for surveying more precision is needed. Toward this end, a variety of means, such as precise levels have been developed, which are calibrated to provide a precise plane from which differentials in height between the instrument and the point in question, typically through the use of a vertical measuring rod.
The basic tool is a theodolite, set on a tripod, with which one can measure angles (horizontal and vertical), combined with triangulation. Starting from a benchmark, a position with known location and elevation, the distance and angles to the unknown point are measured. A more modern instrument is a total station, which is basically a theodolite with an electronic distance measurement device (EDM). Still more modern is the use of satellite positioning systems, such as a Global Positioning System (GPS). Though GPS systems have increased the speed of surveying, they are still only accurate to about 20 mm. It is because of this that EDMDs have not been completely phased out. Robotics allows surveyors to gather precise measurements without extra workers to look through and turn the telescope or record data. A faster way to measure (no obstacles) is with a helicopter with laser echolocation, combined with GPS to determine the height of the helicopter. To increase precision, beacons are placed on the ground (about 20 km apart). This method reaches a precision of about 5 cm.
With the triangulation method, first, one needs to know the horizontal distance to the object. If this is not known or cannot be measured directly, it is determined as explained in the triangulation article. Then the height of an object can be determined by measuring the angle between the horizontal plane and the line through that point at a known distance and the top of the object. In order to determine the height of a mountain, one should do this from sea level (the plane of reference), but here the distances can be too great and the mountain may not be visible. So it is done in steps, first determining the position of one point, then moving to that point and doing a relative measurement, and so on until the mountain top is reached.
Origins
Surveying techniques have existed throughout much of recorded history. In Ancient Egypt, when the Nile River overflowed its banks and washed out farm boundaries, boundaries were re-established through the application of simple geometry. The nearly perfect squareness and north-south orientation of the Great Pyramid of Giza, built c. 2700 BC, affirm the ancient Egyptians' command of surveying.
- The Egyptian land register (3000 BC).
- In Rome, the tax register of conquered lands(300 AD).
- In England, The Domesday Book by William the Conqueror(1086)
- covered all England
- contained names of the land owners, area, land quality, and specific information of the area's content and habitants.
- did not include maps showing exact locations
- Continental Europe's Cadastre was created in 1808
- founded by Napoleon I (Bonaparte), "A good cadastre will be my greatest achievement in my civil law", Napoleon I
- contained numbers of the parcels of land (or just land), land usage, names etc., and value of the land
- 100 million parcels of land, triangle survey, measurable survey, map scale: 1:2500 and 1:1250
- spread fast around Europe, but faced problems especially in Mediterranean countries, Balkan, and Eastern Europe due to cadastre upkeep costs and troubles.
A cadastre loses its value if register and maps are not constantly updated.
Large scale surveys are a necessary pre-requisite to map-making. In the late 1780s, a team from the Ordnance Survey of Great Britain, originally under General William Roy began the Principal Triangulation of Britain using the specially built Ramsden theodolite.
Types of surveys
- ALTA/ACSM survey: a surveying standard jointly proposed by the American Land Title Association and the American Congress on Surveying and Mapping that incorporates elements of the boundary survey, mortgage survey, and topographic survey. ALTA/ACSM surveys, frequently shortened to ALTA surveys, are often required for real estate transactions.
- Boundary survey: the actual physical extent of property ownership, typically witnessed by monuments or markers, such as (typically iron rods, pipes or concrete monuments in the ground, but also tacks or blazes in trees, piled stone corners or other types of monuments) are measured, and a map, or plat, is drawn from the data.
- Deformation survey: a survey to determine if a structure or object is changing shape or moving. The three-dimensional positions of specific points on an object are determined, a period of time is allowed to pass, these positions are then re-measured and calculated, and a comparison between the two sets of positions is made.
- Draw lot: one lot from a plat is drawn, with any easements and setbacks that may be on it.
- Foundation survey: the position of the house is measured before it is finished being built.
- Mortgage survey: a simple survey that generally determines land boundaries and building locations. Mortgage surveys are required by title companies and lending institutions when they provide financing to show that there are no structures encroaching on the property and that the position of structures is generally within zoning and building code requirements. Mortgage surveys are not sufficiently accurate for use in building new structures.
- Physical survey: the finished house and driveway are measured, and all markers on the boundary are indicated. This is recorded when the lot is sold.
- Plot plan: a proposal for a house or other building and driveway or parking lot are added to a draw lot.
- Subdivision plat: a plot or map based on a survey of a parcel of land. Lines are drawn inside it, indicating the location of roads and lots. Plats are usually discussed back and forth between the developer and the surveyor until they are agreed upon, at which point pins are driven into the ground to mark the lot corners and curve ends, and the plat is recorded in the cadastre (USA, elsewhere) or land registry (UK).
- Topographic survey: a survey that measures the elevation of points on a particular piece of land, and presents them as contours on a plot.
- Hydrographic survey: a survey conducted with the purpose of mapping the seabed for navigation, engineering, or resource management purposes. Products of such surveys are nautical charts. See hydrography.
- Construction surveying (otherwise 'lay-out' or 'setting-out'): the process of establishing and marking the position and detailed layout of new structures such as roads or buildings for subsequent construction. In this sense, surveying may be regarded as a sub-discipline of civil engineering.
Surveying as a career
The basic principles of surveying have changed little over the ages, but the tools used by surveyors have evolved tremendously. Engineering, especially civil engineering, depends heavily on the surveyor. Whenever there are roads, dams, retaining walls, bridges or residential areas to be built, surveyors are involved. They determine the boundaries of private property and the boundaries of various lines of political divisions. They also provide advice and data for geographical information systems (GIS), computer databases that contain data on 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, property, and contracts. In addition, they must be able to use delicate instruments with accuracy and precision.
In most states of the U.S., surveying is recognized as a distinct profession apart from engineering. Licensing requirements vary by state, however these requirements generally all have a component of education, experience and examinations. In the past, experience gained through an apprenticeship, together with passing a series of state-administered examinations, was required to attain licensure. Nowadays, many states require a Bachelor of Science in Surveying, or a Bachelor of Science in Civil Engineering with additional coursework in surveying, in addition to experience and examination requirements. Typically the process for registration follows two phases- first, upon graduation, the candidate may be eligible to sit for the Fundamentals of Land Surveying exam, to be certified upon passing and meeting all other requrements as a Surveyor In Training (SIT). Upon being certified as an SIT, the candidate then needs to gain additional experience until he or she becomes eligible for the second phase, which typically consists of the Principles and Practice of Land Surveying exam along with a state-specific examination.
Registered surveyors usually denote themselves with the letters P.S. (professional surveyor), L.S. (land surveyor), or P.L.S. (professional land surveyor), or P.S.M. (professional surveyor and mapper) following their names, depending upon the dictates of their particular state of registration.
Typically a licensed land surveyor is required to seal all plans with a seal, the format of which is dictated by their state jurisdiction, which shows their name and registration number. In many states, land surveyors are also required to place caps bearing their registration number on property corners which they have set.
See also
- Architecture
- Benchmark
- Chain
- Dumpy level
- Geodesy
- Geographic information system
- Geoid
- Geomatics
- Geomatics Engineering
- Global Positioning System
- Jacob's staff
- Point of Beginning
- Real estate
- Royal Institution of Chartered Surveyors (RICS)
- Spirit leveling
- Tacheometry
- Technical drawing
- Theodolite
- Topography
Famous surveyors
- Benjamin Banneker
- Len Beadell
- Daniel Boone
- Admiral John Bossler
- William Austin Burt
- Captain James Cook (navigator)
- Walt Disney (subdivision maps)
- Andrew Ellicott
- John Ericsson
- Sir George Everest
- Peter Fidler
- Sir John Forrest
- Malcolm Fraser
- Captain John C. Fremont
- Carl Friedrich Gauss
- Edmund Gunter
- Thomas Jefferson
- Joseph Jenckes (1656-1740), Governor of Rhode Island
- Harry Johnston
- Lewis and Clark
- Abraham Lincoln
- Liu Hui
- Colonel William Light
- Sir Alexander Mackenzie
- Charles Mason and Jeremiah Dixon
- Metius
- Major Sir Thomas Mitchell
- Peter Pond
- John Septimus Roe
- General William Roy
- Willem Schermerhorn
- David Thompson
- Henry David Thoreau
- Charles Tyers
- Captain George Vancouver
- George Washington
- Per Ivar Gjengedal
External links
- Organizations
- Technology