Introduction to Surveying
Surveying may be divided into Geodetic and Plane Surveying. In Geodetic Surveying, large areas of the Earth’s Surface are involved and the curvature of the Earth is taken into account. In Plane Surveying, relatively small areas are under consideration (less than 250km2 in area) and the Earth’s surface is assumed to be flat (i.e. a horizontal plane). Measurements that are taken in the field are projected onto the horizontal plane before plotting of plans. When connecting Plane surveys to Geodetic surveys, care should be taken to avoid large discrepancies.
Surveys may be classified (according to purpose) as follows: –
Geodetic Surveys: Involve measurements taken to the highest standard for establishment of control networks (e.g. for a whole country). Traditionally these have involved frameworks of angular and distance measurements between points. Modern methods of establishing control networks (e.g. Global Positioning System) that establish three dimensional control networks to high accuracy are in increasing use.
Geodesy: Branch of Surveying involved with the study of the size and the shape of the Earth and its gravity field.
Topographic Surveying: For production of plans and maps of natural and man-made features. Plans are mainly for engineering design and administration while maps have a variety of uses (e.g. navigational, recreational, military etc.).
Engineering Surveying: Includes survey work done before, during and after any Engineering works. Large-scale maps and plans form the basis for design, while the proposed position of any feature must be marked on the ground in a process known as “setting out”. Surveys of “as built” structures are often required and occasionally includes monitoring of movement of large structures (such as dams and large buildings).Cadastral Surveying: Undertaken to produce plans of property (showing boundaries) and other data for legal purposes to enable registration of title or other entitlement to land.
Photogrammetry and Remote Sensing: This involves use of photographic and satellite imagery to determine shapes, sizes and positions of objects. It is an indirect method of measurement since it the images rather than the objects themselves that are scrutinized. Some linear and angular measurements may be made in the object-space for control purposes. This method is particularly useful where direct measurement may be impracticable, impossible or uneconomical.
Hydrographical Surveys: Concerned with measurement and production of charts, plans and maps covering harbours, lakes, rivers and associated structures in those areas. It includes measurement of tides, determination of bed depths, and determinations of direction of currents.
Mining Surveying: Involves measurement to provide plans, maps and charts for mines. It includes control networks that relate surface control to underground control.
Geographical/ Land Information Systems: Concerned with collection, storage, analysis and dissemination of land information, primarily by use of computers to facilitate complex analyses of information to make faster, timely and more informed decisions.