Global Positioning System
The global positioning system (GPS) is a space-based satellite navigation system that provides users with a highly accurate three-dimensional positioning information (longitude, latitude and elevation) as well as time. GPS technology is useful in performing tasks requiring high precision, such as crop mapping, automatically driven farm vehicles, soil sampling, and distribution of fertilizers and pesticides at variable rates. Today, many growers use GPSderived products to enhance operations in their vineyard operations. The accuracy of GPS allows growers to create vineyard maps with precise acreage for vineyard blocks, road locations and distances between points of interest. Global positioning systems allows growers to accurately navigate to specific locations in the vineyard, year after year, to collect soil samples or monitor crop conditions. Combining GPS and geographic information systems (GIS) has enabled the coupling of real-time data collection with accurate position information, leading to the efficient manipulation and analysis of large amounts of geospatial data.
Every time a GPS receiver calculates its position, there is some amount of error inherent in the calculated position. Errors can be introduced from a number of sources (e.g., GPS clock errors, atmospheric conditions, the distribution of GPS satellites) over which the GPS user has little control. The most common way to counteract GPS errors is by using Differential GPS or DGPS.
Several coordinate systems are in use for mapping and may cause problems with compatibility between software systems. Users frequently need to transform position data into a plane (flat) coordinate system, either to merge them with another data set, to plot a map of the GPS results, or to perform further calculations for such parameters as area, distance or direction (plane coordinate systems are usually easier to work with than geodetic coordinates). When using data and maps from several sources, coordinates must be based on the same datum. The coordinate system differences, which are caused by a different reference frame, ellipsoid and data adjustment, are significant (up to several hundred meters) and cannot be ignored.
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