TYPES OF SURVEYING & LEVELLING

TYPES OF SURVEYING & LEVELLING

Types of Surveying

There are many types of disciplines in surveying and a surveyor during their career may decide to specialise in a particular discipline or may gain experience in all disciplines.  The main disciplines of surveying are:

Land surveying:

Land surveying involves measuring and determining property boundaries, which are used as the basis for all property transactions including buying, selling, mortgaging and leasing.  Due to the importance of having a secure and strong property market, in NSW a land surveyor needs to be registered to be able to carry out a land survey.

Engineering surveying:

Engineering surveyors are engaged in the construction industry and ensure construction works are built in the correct location and as per their design.  They are generally found on construction sites setting out various types of works such as buildings, roads, bridges, tunnels and various other forms of infrastructure.

Mining surveying:

Mining surveyors are involved in the development and construction of mining operations and can generally be found above and underground taking measurements to determine volumes and setting out new excavations and tunneling.  Mining surveyors in NSW are registered due to many safety issues involved in mining including ensuring mining does not encroach upon hazardous areas and future subsidence.Hydrographic surveying:

        Hydrographic surveying involves locating and measuring points under the sea and on the shore.  There measurements are used to design infrastructure such as docks and jetties as well as ensuring ships have enough clearance from the sea bed to safely travel around the world.  Using sonar scanners they are able to provide a picture of the sea bed without needing to

get their feet wet and enabling the discovery of ship wrecks and other objects lost at sea.

Geodetic surveying:

Geodetic surveyors are involved with undertaking very precise measurements to determine the shape and size of the world and track the movement of continents.  Their measurements are used in the monitoring of sea level rise, earthquakes, and the tracking of satellites.  Geodetic surveyors are involved in the development of co-ordinate systems and datum’s which are used in the productions of maps and plans.

                                              

Photogrammetry and remote sensing:

Photogrammetry and remote sensing involves taking measurements of the world via photography or other wavelength bands such as infra-red or ultra-violet.  Measurements may be sources from aerial photography or satellite imagery.  Photogrammetry and remote sensing is used to map large areas and determine changes in the world over time.

Mapping:

          The making of maps (Cartographic) has become as high-tech as any other industry with Images taken by air craft and satellites.  The cartographic then uses these images combined with other information about the area to construct the maps.

Environmental Planning:

Survey are involved in research projects such as global warming, monitoring of existing environments such as whale moments in the waters off the north coast of new south wales and providing environmental impact statements for new development.

GPS Satellite Surveying & Satellite Imagery:

Surveyors use Global Positioning System (GPS) in all kind of Surveying. Satellite imagery is also being used to monitor movements on the Earth’s surface earth quake zones potential mud solid or even troops on the move in a war zone.

Types of Leveling:

Leveling is the measurement of geodetic height using an optical leveling instrument and a level staff or rod having a numbered scale. Common leveling instruments include the spirit level, the dumpy level, the digital level, and the laser level.

Spirit (optical) leveling:

Spirit leveling employs a spirit level, an instrument consisting of a telescope with a crosshair and a tube level like that used by carpenters, rigidly connected. When the bubble in the tube level is centered the telescope's line of sight is supposed to be horizontal (i.e. perpendicular to the local vertical).

The spirit level is on a tripod with sight lines to the two points whose height difference is to be determined. A graduated leveling staff or rod is held vertical on each point; the rod may be graduated in centimeters and fractions or tenths and hundredths of a foot. The observer focuses in turn on each rod and reads the value. Subtracting the "back" and "forward" value provides the height difference.

If the instrument is placed equidistant from the two points to be measured, any small errors in its adjustment and the effects of earth curvature and refraction will tend to cancel out.

Leveling procedure:

A typical procedure is to set up the instrument within 100 meters (110 yards) of a point of known or assumed elevation. A rod or staff is held vertical on that point and the instrument is used manually or automatically to read the rod scale. This gives the height of the instrument above the starting (back sight) point and allows the height of the instrument (H.I.) above the datum to be computed.

The rod is then held on an unknown point and a reading is taken in the same manner, allowing the elevation of the new (foresight) point to be computed. The procedure is repeated until the destination point is reached. It is usual practice to perform either a complete loop back to the starting point or else close the traverse on a second point whose elevation is already known. The closure check guards against blunders in the operation, and allows residual error to be distributed in the most likely manner among the stations.

Some instruments provide three crosshairs which allow stadia measurement of the foresight and back sight distances. These also allow use of the average of the three readings (3-wire leveling) as a check against blunders and for averaging out the error of interpolation between marks on the rod scale.

The two main types of leveling are single-leveling as already described, and double-leveling (Double-rodding). In double-leveling, a surveyor takes two foresights and two back sights and makes sure the difference between the foresights and the difference between the back sights are equal, thereby reducing the amount of error. Double-leveling costs twice as much as single-leveling.