SURVEYING is the technique and science of accurately determining the terrestrial or three-dimensional space position of points and the distances and angles 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 maps and boundaries for ownership or governmental purposes.A surveying point in Germany

 

Even though remote sensing has greatly speeded up the process of gathering information, and has allowed greater accuracy control over long distances, the direct survey still provides the basic control points and framework for all topographic work, whether manual or GIS-based.

 

In areas where there has been an extensive direct survey and mapping program (most of Europe and the Continental US, for example), the compiled data forms the basis of basic digital elevation datasets such as USGS DEM data. This data must often be "cleaned" to eliminate discrepancies between surveys, but it still forms a valuable set of information for large-scale analysis.

 

The original American topographic surveys (or the British "Ordnance" surveys) involved not only recording of relief, but identification of landmark features and vegetative land cover.

 

HISTORY

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 Egyptians' command of surveying.

 

      The Egyptian land register (3000 BC).

      Under the Romans, land surveyors were established as a profession, and they established the basic measurements under which the empire was divided, such as a 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.

 

 

Surveying Instruments

 

 

A theodolite is an instrument for measuring both horizontal and vertical angles, as used in triangulation networks. It is a key tool in surveying and engineering work, but theodolites have been adapted for other specialized purposes in fields like meteorology and rocket launch technology. A modern theodolite consists of a telescope mounted movably within two perpendicular axes, the horizontal or trunnion axis, and the vertical axis. When the telescope is pointed at a desired object, the angle of each of these axes can be measured with great precision, typically on the scale of arcseconds.

 

A total station is an optical instrument used in modern surveying as well as by police, crime scene investigators, private accident reconstructionists and insurance companies to take measurements of scenes. It is a combination of an electronic theodolite (transit), an electronic distance measuring device (EDM) and software running on an external computer.

 

The 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.

 

Chains and Tapes were also traditionally used to measure distances in land surveys. These can still be used today for small short distance surveying, while most distancing is done with laser distance finders today.

 

 

 

 

 

 

GO BACK

 

 

LINKS

http://en.wikipedia.org/wiki/Surveying

http://en.wikipedia.org/wiki/Total_station

http://en.wikipedia.org/wiki/Theodolite

http://www.surveyhistory.org/