How GPS Works in a Car: The Complete Guide
With so many remakes of classic films and film ideas, it’s amazing there isn’t a new Cannonball Run. Maybe the advance of GPS has made the concept unworkable.
Like many modern conveniences, GPS seems to be everywhere and used by everyone. Still, have you ever found yourself asking how GPS works?
The usefulness of the service is obvious. Improvements in equipment and concept have increased the once lofty 7.8-meter accuracy to a new standard accurate to within 4.9 meters.
Improvements currently announced claim even higher levels of precision. What are they changing and how does it affect a technology that has existed since the 1960s? Read on for details galore.
How GPS Works: The Tech
First, definition of terms.
You probably know that GPS stands for Global Position System. What you are less likely to know is that the System represents 32 US launched satellites.
Russia has a similar set of satellites known as GLONASS. (It’s an acronym largely in Russian, so we’ll leave it out here.) Together, these two entities work together and share resources with the ICAO (International Civil Aviation Organization).
The ICAO creates the codes and protocols that let every nation access the two large satellite arrays in addition to tertiary satellites added by companies and smaller national efforts.
You might use GPS as shorthand to mean any navigation system, but the Global Navigation Satellite System (GNSS) is actually a shell that uses GPS.
Satellites are the core of how GPS is explained. Receiving units are the terrestrial component needed. This sounds simple enough, conceptually.
The real workhorse of the process comes from how these systems interact. This has two components timing and positioning. Let’s explore how we achieve these two feats.
Just like in comedy, for GPS to function, timing is everything.
The satellites utilize sophisticated atomic clocks to provide time measurements. These have to be accurate to nanoseconds. They also need to receive and transmit information many time each second.
The ground unit requests information in the form of a ‘ping’ from a designated satellite. The satellite compares the timestamp from the sent signal to the timestamp after the process received it.
Calculations are also made for how long the signal took to arrive. Signal speeds change as they move through the troposphere and ionosphere. The satellite has to adjust for all of this to give accurate information.
Once a signal is received and calculated, a response is sent back, with additional adjustments for how long it will take the signal to get back to the transmitting device.
Triangulation vs Trilateration
If you have done much manual navigation or signal tracking, you understand the idea behind triangulation. Measuring angles from three different sources enables you to arrive at detailed results.
Triangulation is used to determine distance, time, and height of objects with unknowns.
Trilateration measures distances. When a device sends a GPS signal, it doesn’t go to just one satellite. It doesn’t even go to the nearest three satellites.
Near and far don’t matter for the trilateration calculation. The only thing that needs to be known is the time. That’s why the atomic clock is the first important step in answering ‘How does GPS navigation work?’
Once a ground-based device sends a trio of signals and a trio of satellites receives them, your position is known.
The improvements in accuracy seen over the decades of GPS technology come from the speed of processing.
In recent years, the advancements in tech are revealed at the annual ION GNSS+ showcase.
Faster chips in the satellites and the ground-based units give the same accuracy in timing but are better able to correct for your movement during data transfers.
Extra signal frequencies provide backups so you don’t get false positions from signal bounce. If you have ever been lost in the city or a canyon, you know how bad signal bounce can be.
As tech advances, new applications become possible. Take a look at our article on motion sickness intervention.
How GPS Works: Navigation (GNSS)
Now that you understand how GPS knows where you are, let’s look at how it knows where you are going.
Since 2008, more devices have been developed to work without wi-fi or data signals. For early adopters that were using GPS in the 90s, you already know how this basically works.
Rather than update the maps on the fly, these devices download maps ahead of time and then update positions with GPS signals.
To provide the best in satellite navigation, modern devices use digital maps that represent the local area. Many of these maps were originally formed by satellites but have improved since.
Projects like Google Street View filmed and modeled miles upon miles of roads to adjust the satellite images into more discrete units.
From there, your relative speed is determined and the system in the car itself takes over doing the bulk of the calculations. The car unit updates and receives new information from the satellites but not constantly.
The map tool knows the distances between objects. It also knows your speed. From there, it is possible to guide or direct you without GPS at all. The GPS serves an essential purpose in building accurate maps for the unit but continues to be used as a backup, not the primary tracker.
Satellite navigation through GPS also gathers information from other broadcasting sites. Street lights, businesses, and other devices through the same service provider all provide relative information. Together, these systems give an accurate map of the world even outside the mapping information in the car unit.
These overlapping, partially redundant, systems create an ever increasing accuracy for tracking and guiding you through the world.
All the Best
How GPS works differs from one unit to the next. Part of this is the service provider and part is the features of the device.
Integrated voice through your car’s sound system works better than a speaker from a phone. Integrated systems also track from the car and don’t get confused as easily with signal bounce.
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