Last edited 02 Sep 2016

Land surveying


[edit] Introduction

Land surveying is a process for determining distances and angles between points on land. Land surveyors use traditional instruments and digital technology, to produce surveys, data and maps describing the Earth’s surface features. This is essential for civil engineering and construction projects.

Land surveying is a historic practice, with the first land surveys dating back nearly 3,000 years to Ancient Egypt, where surveyors subdivided fertile land around the Nile River after annual flooding.

Modern land surveyors use technology such as robotic total stations and theodolites to precisely map an area. This collected data can then be manipulated by computer aided design (CAD), building information modeling (BIM) or geographic information systems (GIS) software. For more information, see Surveying instruments.

[edit] Types of land survey

Land surveys can be divided into three basic categories:

  • Standard land surveys: Describing boundary lines, calculating land areas, and so on.
  • Engineering surveys: Ensuring a building is constructed in the correct place, and so on.
  • Informational surveys: Used to create maps and charts.

Land surveys can also be classified as geodetic or plane surveys:

  • Geodetic surveys tend to cover large areas, and must take into consideration the Earth’s curvature in order to achieve precision. These surveys require techniques such as triangulation and trilateration.
  • By contrast, plane surveys consider the Earth’s surface as a flat plane, with curvature not taken into consideration. These tend to be used for smaller areas. Techniques required include plane trigonometry and plane geometry.

[edit] Land surveying uses

Land surveying can be used to establish boundaries for ownership. Information about boundaries is important as it helps determine where roads or buildings will be constructed, helps to settle property line disputes, and enables the development of land maps.

Other common uses of land surveying include:

  • Initial surveys and environmental impact assessments of potential sites for construction.
  • Geospatial measurement – charting exact coordinates of site features.
  • Setting out - Establishing building lines and road alignments on site, as described by drawings (effectively the reverse of surveying).
  • Photogrammetry – producing digital images of sites.
  • Remote sensing – mapping land use with satellite photography.
  • Geomatics – gathering data and using GIS to analyse and interpret site features.
  • Geomechanics – monitoring land movement and subsidence as a result of construction works or natural processes.
  • Draughting 2D and 3D charts and maps.
  • Hydrographic surveying – gathering data for canals, dredging operations, navigational charts, oil and gas exploration, undersea mining, locating and salvaging sunken ships, and so on.

[edit] Land surveying techniques

The type of land survey technique adopted will depend the type of survey that is being undertaken.

[edit] Triangulation

Triangulation uses a series of connected triangles from which angles can be measured from determined stations. This is an efficient technique as it minimises the number of necessary measurements.

[edit] Trilateration

Trilateration calculates angles using electronic distance-measuring equipment to measure the lengths and sides of the triangles that are used in triangulation. This is often used in areas of uneven topography or rough terrain to produce more accurate calculations.

[edit] Traverse

The traverse technique uses a series of lines, of measured distances and lengths, that are connected together by points in determined locations. Traverse lines can be open or closed and adjusted to take account of obstructions, rough terrain, and so on. This is often used for the preliminary surveys of new roads.

[edit] Levelling

Levelling is the process of determining the height of one level relative to another. It is used in surveying to establish the elevation of a point relative to a datum, or to establish a point at a given elevation relative to a datum. The difference in elevation between two points can be established by using trigonometry.

[edit] Radiation

Radiation uses a fixed position above a ground location from which various points are taken at the boundary of the survey area. The points are plotted and distances measured and converted to the required scale on the survey sheet. It is most commonly used in conjunction with a plane table (a device used to provide a solid and level surface on which to make drawings, charts and maps), as well as with techniques such as traverse and triangulation.

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