Using GPS Technology for Land Survey

Using GPS Technology for Land Survey

GPS is the acronym for Global Positioning System. It is a highly accurate navigation system using signals from satellites to determine a location on the Earth’s surface, irrespective of weather conditions.

GPS depends on satellites high above the Earth to transmit signals which contain the time and location of the satellite. Any ground-based receiver which receives signals from four or more GPS satellites can use navigation equations to calculate its location on the Earth’s surface. Continued signals help update speed and direction information for moving receivers.

Although GPS was originally developed for military use it has since been made available for civilian use and is now used in such common applications as mobile phones, and car navigation systems, and of course, it is also used in surveying and mapping.

HOW GPS IS USED IN LAND SURVEYING

GPS technology is often incorporated into a Total Station to produce complete surveying data. Receivers used for baseline measurements are generally more complex and expensive than those in common use, which usually require a high-quality antenna.

Surveying and mapping were one of the first commercial adaptations of GPS, as it provides a latitude and longitude position directly without the need to measure angles and distances between points.

GPS is widely used in surveying, however, it hasn’t entirely replaced surveying field instruments such as the theodolite, Electronic Distance Meter, or the more modern Total Station.

Surveyors use either of these three methods of GPS measurement:

• RTK Observations: This means Real Time Kinematic observations which happen when a receiver remains in one position over a known point – the Base Station – and another receiver moves between positions – the Rover Station. The position of the Rover can be computed and stored within a few seconds, using a radio link to provide a coordinate correction. This method is accurate to within 10km of the base station.
• The static GPS Baseline: This method is used to determine the accuracy of coordinates for survey points by simultaneously recording GPS observations over a known and unknown survey point for at least 20 minutes. The data is processed to provide coordinates with an accuracy of better than 5mm depending on the duration of the observations and satellite availability at the time of the measurements.
• The Continuously Operating Reference Stations (CORS): This is where a survey quality GPS receiver is permanently installed in a location as a starting point for any GPS measurements in the district, area, or region. Surveyors’ GPS receivers can then collect field data and combine it with the CORS data to calculate positions. CORS is used commonly in major engineering projects and by local governments. 

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