Field inspectors, maintenance teams, utility crews, and emergency workers all require timely access to enterprise GIS data so they can make informed decisions. To facilitate the flow of information to and from the field, mobile GIS solutions leverage advances in wireless technology and the Internet.
With mobile GIS, data is directly accessible to field-based personnel whenever and wherever it is needed. A GPS receiver must acquire signals from at least four satellites to reliably calculate a three-dimensional position. Ideally, these satellites should be distributed across the sky.
The receiver performs mathematical calculations to establish the distance from a satellite, which in turn is used to determine its position. The GPS receiver knows where each satellite is the instant its distance is measured. This position is displayed on the datalogger and saved along with any other descriptive information entered in the field software.
GPS can provide worldwide, three-dimensional positions, 24 hours a day, in any type of weather. However, the system does have some limitations. There must be a relatively clear "line of sight" between the GPS antenna and four or more satellites.
Objects, such as buildings, overpasses, and other obstructions, that shield the antenna from a satellite can potentially weaken a satellite's signal such that it becomes too difficult to ensure reliable positioning. These difficulties are particularly prevalent in urban areas. The GPS signal may bounce off nearby objects causing another problem called multipath interference. Until , civilian users had to contend with Selective Availability SA.
The stationary receiver is the key. It ties all the satellite measurements into a solid local reference. Remember that GPS receivers use timing signals from at least four satellites to establish a position. Each of those timing signals is going to have some error or delay depending on what sort of perils have befallen it on its trip down to us. For a complete discussion of all the errors review the "Correcting Errors" section of the tutorial.
Since each of the timing signals that go into a position calculation has some error, that calculation is going to be a compounding of those errors. Luckily the sheer scale of the GPS system comes to our rescue. The satellites are so far out in space that the little distances we travel here on earth are insignificant. So if two receivers are fairly close to each other, say within a few hundred kilometers, the signals that reach both of them will have traveled through virtually the same slice of atmosphere, and so will have virtually the same errors.
Differential GPS can eliminate all errors that are common to both the reference receiver and the roving receiver. These include everything except multipath errors because they occur right around the receiver and any receiver errors because they're unique to the receiver. That's the idea behind differential GPS: We have one receiver measure the timing errors and then provide correction information to the other receivers that are roving around.
That way virtually all errors can be eliminated from the system, even the pesky Selective Availability error that the DoD puts in on purpose. The idea is simple. Farmers now know how to further improve seed germination techniques, prevent weeds and pest infestation, and maximise overall crop yields.
Data collecting is now a necessary task for many of them. Vantage NSW is a trusted name among farmers and agricultural professionals when it comes to GPS correction services and precision agriculture solutions for all seasons, terrains, crops and vehicles.
We are the authorised distributor of Trimble, a company that knows that farmers need accurate data for their farming needs. Learn more on our website and enquire about Differential GPS and our other correction services.
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