Land Surveying and GPS Articles | Land Surveying

By: Charles Iner

Land surveyors once used tape measures and transits to measure distances and positions. Since the 1980s, electronic distance measurement, or EDM, devices have allowed for much more efficient and accurate measurements. These use a wave of energy that is shot between the EDM instrument and a reflector. The time the beam takes to return is then calculated as distance. Today, such calculations can be done using sophisticated GPS systems.

The Global Positioning System uses a network of satellites to precisely pinpoint the device's location on Earth at any moment. GPS uses the principle of trilateration, using the location of several satellites to pinpoint an exact location. A receiver can determine the latitude, longitude, and elevation of a point using four or more satellites; there are a total of 24 Global Positioning System satellites currently in use. First created by the U.S. Department of Defense as a navigational aid in 1994, today it is used in many devices, tracking everything from cell phones and delivery vehicles to the movement of the tectonic plates of Earth's crust.

Land surveyors use Global Position Systems to note the precise coordinates of spatial locations. Exact measurement of these positions is one of the fundamental elements of land surveying. The benefit of is that it is much more accurate than hand-measuring these locations. There is some degree of error in all land surveying measurements, due to human errors, environmental characteristics like variations in magnetic fields, temperature, and gravity, and instrument errors. GPS allows for much more precise measurements than previously available to land surveyors using measuring tape and an angle sight.

Another benefit of the use of its use as a land surveyor is that the coordinates can be located precisely, while other methods of land surveying rely on measurements from other known locations, such as the edge of the property line, the corner of a house, or another landmark. These locations could change over time, such as if a house is torn down or another obstacle is built between the structure and the measured point; even a surveyor's stake may be removed before the land is re-surveyed. The coordinate of a given location on Earth, however, remains the same. Therefore, using GPS as a land surveyor produces measurements that will be accurate no matter what happens to the surrounding land.

Although Global Position System receivers allow for very precise measurements, there is still a degree of error involved. A receiver on a tripod will record the location slightly differently each time; when many measurements are taken, these data points will form a cluster around the actual location. Better-quality receivers, of course, reduce this amount of error. Survey-grade receivers, rather than those meant for non-surveying uses, may produce a group of measurements clustered within just one centimeter of the actual location. Today's receivers are steadily gaining in use, but may not be as accurate as the surveyor would like, especially in areas that are heavily wooded or which have other large obstructions. However, the technology is rapidly advancing and gaining a foothold in the available equipment for land surveyors. Since 1994, the accuracy available when using GPS units has improved steadily.