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Global Positioning System (GPS) is new tool used for either positioning of ground locations or as for surveying. It has become very popular among professionals ranging from surveys to engineers to archaeologists. Many of them have are using GPS on their survey work. For many of us, GPS may seems complicated, but the principle is very simple. GPS stand for Global Positioning System which is a tool used for locating ourselves on the earth. This tool ( based on satellite communication system) was used by United States Military and later extended to civilian use. It uses 4-orbital satellites (moving along 6-orbital planes) orbiting at an altitude of approximately 20200 Km every 12 hours. The communication or carrier waves broadcast from these satellites are used to location on a given ground position. In essence, the GPS system uses a radio receiver (located on ground) that receive signal from satellites thereby locating its geographic coordinates. More specifically, the ground receivers will transmit its positions and time by making simultaneous measurements to the satellites. Then three orbiting satellites will derive the 2-d dimensional position or location. If 3 dimensional coordinates (latitude, longitude and height) are needed, it is essential to communicate with minimum of four satellites within the signal range. Use of GPS in Surveying GPS seems to be an excellent technique for surveying. In many civil engineering fieldwork, GPS is used widely at present. It is mainly used for mapping, exact location or the spots, earth work, topographic surveys. In combination with other latest techniques GPS has become a ready substitute for the conventional surveying techniques. The selection of the type of GPS depends on the level of accuracy expected. Many engineers may be happy with the degree of accuracy possessed by hand-held GPS. This has been an essential item ( or surveying tool) for field investigation and reconnaissance work. The hand held GPS may not be the best equipment, where accuracy within a meter is required. For example, for surveying involving trench stakeouts, contour surveys and recording of sites at scales up to 1:2500, using of Differential GPS may be appropriate. For more precise recording, such as grid layouts, excavation plans and topographical surveys, Carrier-Phase GPS will have to be used. Thus implying very high level of accuracy up to millimeter. GPS Compared to Total Station Until recently the Total Station Theodolite (TST) has become the preferred tool for setting out of trenches, surveying sites or topographical surveys. Frequently in archaeological work, Now GPS has become the popular tool for many surveying professionals. GPS has outperformed TST when the work has to be done: Where sites are remote and has limited access, hard details are not available, and positioning may be unreliable. Where more man power is required, where line of sight cannot be maintained between the instrument and prism. where no dependency can be maintained on permanent landscape features. when there is no dependency on a maintained line of sight between the base receiver and rover. In addition, GPS may need less man power and less time to complete same coverage of TST. In other words, both setting up and surveying time is considerably reduced. When using GPS, one should know the pros and cons of GPS. There are limitations associated with GPS. Since, this system depends on communication with satellite system, when carrying out GPS surveys, clear sky has to be there always. Similarly, you may notice poor satellite signal reception when in thick forest cover or close to tall buildings. Finally, it is essential to know the cost of GPS. The cost of GPS may vary according to the level of accuracy you need. The accuracy comes with a price tag.
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Land Surveys Pty Ltd are one of Perth's premier surveying companies and providing surveying services and GPS mapping services in Western Australia.
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