GPS Machine Control Home
GPS Info:
What is GPS
How GPS Works
GPS Systems Accuracy
- US GPS
- Soviet GLONASS
- EU Galileo
- Why GPS, GLONASS & Galileo
Machine Control GPS:
How GPS Machine Control Works
- Base Stations intro
- Radio Base Stations
- GPS and RTK accuracy
- GPS + Laser = MM Accuracy
- GPS + Cell = 1200+ Sq Miles
- GPS on Machines
- GPS Control Boxes/Computers
- GPS Automate Vs. Indicate
GPS System Benefits:
GPS Machine Control Benefits
- Billing Controls
- Data and Management
- Job Management
- Move Dirt 1 Time!
- Many Machines
GPS Parts, Prices, and More:
GPS Machine Control Parts & Cost
- Pricing Automate vs Indicate
- GPS for Graders
- GPS for Dozers
- GPS for Blades
- GPS for Scrapers
- GPS for Excavators
Informative Grade Sites:
AccurateGrade.com
- Precision Grading Practices
LowCostMachineControl.com
- Laser Machine Systems
Sponsors:
Rocky Mtn Lasers
Construction Lasers
Construction Directory
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GPS Accuracy
A Little More About GPS Accuracy
Did you notice that when accuracy is specified it’s described as “horizontal” accuracy? This is because GPS supplies a higher degree of horizontal accuracy than it does vertical accuracy.
It can plot your latitude and longitude very precisely. But elevation, or vertical accuracy, is more difficult. That’s because all the GPS satellites are overhead, so there can be a wide range of horizontal bearings (virtually from one horizon to the other). But since no GPS satellite signals are available from below the receiver, it’s impossible to have a larger range of vertical points.
So what is a typical vertical accuracy for GPS RTK systems? From two to three times less accurate that of the horizontal accuracy, which should be anywhere from ½ to ¾ inch (12 to 18mm). Of course, the more GPS satellites you are receiving, the better your vertical accuracy will be.
GPS Precision Has A Price
There are many factors associated with using the GPS system and getting the precision you require. There’s a huge difference between knowing where you are within 30 feet (10 meters) and knowing where you are within ¼ inch (6mm). You can buy an inexpensive, handheld GPS receiver for around $1000 that will provide location information within a horizontal tolerance of ±30 feet (10 meters). However, a GPS system that can provide accuracy to within ¼ inch (6mm) requires much higher sophistication and a much larger investment.
But why is that? They both use the same satellite signals, right? Simply put, a basic system must deal with a few obstacles such as:
- GPS Satellite drift;
- GPS “Multipath” Signals (false signals that are generated when a true signal bounce off the ground or nearby structures).
- GPS Signal Refraction of the radio waves as they go through the earth’s atmosphere
- Radio and other interference
To overcome these obstacles, suppliers have created GPS systems that provide many standard features and options to give the most precise, real-time positioning information for your application.
To compensate for GPS satellite drift, GPS providers maintain the position of all the GPS satellites in view, and reference each GPS satellites precise orbit relative to each other. This way, drift can be corrected for.
To eliminate multi path errors, antennas are designed to “look” nowhere but up, and utilize filtering software that kicks out suspected “signal bounce”
To eliminate errors caused by the earth’s atmosphere, a secondary receiving station called a “base station” is set up over a known, surveyed point. This known coordinate is input into the base station, and then as it receives satellite information, it compares that data to its known location and continually transmits “correction” data to the “roving” GPS receivers and GPS machine control units on the job site. This correction data is then used in conjunction with the GPS satellite signals received by the moving GPS system to provide highly precise information despite the motion.
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