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