Surveying is process which measures the dimension of an object that generally present on the surface of the Earth. The equipment which are used frequently for surveying includes levels and theodolites. These are used for precise or accurate measurement of angles, horizontal, vertical and slope distances. With the improvement of computer based technology such as electronic distance measurement (EDM), total stations, Geographic Positioning Systems (GPS) the traditional optical instruments have been replaced. Although, Land Surveying is common to all types of surveying, there are noticeable differences between land surveying and construction surveying.
Land Surveying Vs Construction Surveying
In many countries, Land Surveying is considered to be a distinguishable profession. For example, Land Surveyors have their own professional associations and licensing criteria. The licensed land surveyor performs boundary surveys and subdivision plans. Whereas construction surveying is generally performed by specialized well trained technicians. When compared with the land surveyors, the plans prepared by the construction surveyors do not have legal status.
Main features or task under construction surveying are as follows:
Surveying of existing ground conditions of new construction site. This will cover, topography of site, measuring and recording the condition of existing buildings and infrastructure. Similarly measuring invert levels and dimensions of sewers and manholes that comes underground infrastructure.
Setting-out or layout of proposed building site, and building location. Fixing of datums or reference or control points that will guide the construction of new structures such building, roads, canals and sewers, etc. Also, the construction surveying will ensure that there will not be major deviations from the planned construction based on the established reference points and markers. For example, the reference points or markers are established according to an arbitrary coordinates system. The continuous monitoring based on the reference points and base lines, the construction surveyor verify the location of structures while construction and do the necessary correction if needed.
Preparation of As-Built Plans to ensure that the construction project or the building project was done according to the approved local authority drawings, specifications and regulations.
The Construction Surveying needs coordinate System. For example,
Arbitrary Coordinates based on Geodesic Coordinates
During construction surveying it is common to use arbitrary construction coordinate system. The arbitrary coordinate system is derived from the geodesic coordinates.
In the case of linear measurements (of roads, buildings) often a chainage or distance will be established from fixed based line such as the center line of the road. During construction, the building or other structures will be located with respect to chainage, offset, elevations, etc.
Building Axes are also have to be established in the case of construction of buildings. These axes are often fixed along the building column or foundation grids or major load bearing walls.
In construction or building projects an arbitrary reference lines may be established either north-south or east-west directions. It may not necessarily be based on true coordinates.