Motorcycles and GPS: Satellite Navigation, Part 1

Dec 20, 2014 View Comments by

A Motorcyclist’s 
Guide to the Galaxy: Satellite Navigation, Part 1Navigation: A Modern-Day Necessity for Riders
For motorcyclists, navigating from one point to another was previously quite a demanding task. Working out the maps required a lot of skill and time, holding many maps took space, as well as continuously determining the current position of the motorcycle, all while exposed to the elements. In recent years, satellite navigation has become accessible and available to consumers, due to mass production, drop in prices, and smaller sizes. In particular, it has become very useful for motorcyclists.

Yet it seems that many riders are struggling to understand this technology and how to efficiently utilize it.

This multi-part series will explain in laymen’s terms how satellite navigation works, how to use it resourcefully, importing routes created by others, and best practices in designing routes from scratch. I’ll also cover what routes and tracks are, the other functions of the satellite receiver, different types of devices, the receiver database, mounting, wiring, and more.

But first, I’ll start with the basic concepts and then gradually move to more advanced topics. I will attempt to simplify the explanations for easy understanding.

Types of Satellite Navigation Systems
Satellite navigation is used because it is a more generic term than GPS. GPS is a system operated by the U.S. Department of Defense and was initially designed for military usage but was later opened up to civilians. There are other Global Navigation Satellite Systems (GNSS), such as the Russian GLONASS, or the European Galileo, which should become operational in 2020. These systems are supposed to have much higher accuracy than the other systems (approximately one yard for open access and a few centimeters for commercial usage). GPS has become so popular that most people now use it as a synonym for satellite navigation. However, it is important to know that there are other systems, and the principles explained here are not specific only to the U.S. operated GPS.

A Motorcyclist’s 
Guide to the Galaxy: Satellite Navigation, Part 1How Does Satellite Navigation Work
So what is a GNSS and how does it work? It is a constellation of satellites floating in near space—around the Earth—covering it globally. Each satellite has a very accurate atomic clock, and it emits a message repeatedly using radio communication. All the satellites are synced to the same exact time, and they basically send a message that looks similar to this: “I’m satellite number seven, and my time now is 13:04:05:00.”

First, Calculate Correct Time
By listening to these messages from just one satellite using a satellite receiver device, e.g. ‘the motorcycle GPS’ or a smartphone, it is possible to know the current time with high accuracy, on virtually any point on Earth. This solves the ancient problem of figuring out the current time and also the reason why your motorcycle GPS receiver always shows the correct time. It never needs adjustment, unlike the motorcycle clock (for those that have it) that continuously drifts out of sync, or gets reset when the motorcycle battery is removed.

A Motorcyclist’s 
Guide to the Galaxy: Satellite Navigation, Part 1Second, Determine Location and Distance
The satellite receiver on the ground has an antenna that is listening to these radio broadcasts. It measures the difference in time between its internal time and the satellite’s time. This time difference is converted to a distance. As we learned in school, distance equals time multiplied by speed, which is the speed of light in this case since the message from the satellite travels as radio signals.

Imagine a sphere where the satellite is at its center—a point which is calculated from the identity of the satellite in the message—since satellites travel in well-known paths. The distance from one satellite means that the receiver point is somewhere on the surface of that sphere. There are infinite possible points all equally distanced from the center of that sphere. But, which point is the right one? For the receiver to know the right point, it needs four distances using a process called trilateration. It receives time signatures from other satellites and calculates four distances. The distances from each satellite are slightly different because it takes time for the radio signal to travel from space to the ground—and even though the speed of light is very fast—it is still a finite speed, and different distances result in very small time differences. The receiver then intersects the four spheres represented by each distance into a single point in space—that point is where the receiver is located.

At that moment, the receiver knows its exact location as three dimensional coordinates relative to the center of Earth. And, it converts it into latitude, longitude, and elevation. If you select the ‘Where am I?’ option on your GPS device, it shows you precisely this information.

A Motorcyclist’s 
Guide to the Galaxy: Satellite Navigation, Part 1Third, Know Your Speed
With that calculated point in hand, interesting things can be done. If the point is re-calculated at every time interval (say every one second), the receiver can measure the distance between the previous point and the current point, and divide it by the time interval. That would give speed. The next time you look at the GPS and see the speed displayed, you will know how it was calculated.

Accumulated travel distance and direction of travel are calculated in a similar way.

I was asked a few times: “How come the motorcycle’s indicated speed and the GPS speed are different?”

Motorcycles typically measure speed from the front wheel or from the transmission. Both are inaccurate. As the former is affected by tire diameter, diminishing tire sizes due to wear or changing tires from stock sizes will cause errors. For the latter, it is measuring a secondary factor—it’s not the motorcycle speed directly—but changing sprocket sizes that introduces errors. But, the main issue occurs because some manufacturers intentionally increase the displayed speed by up to 10 percent (for legal reasons) to make the rider go slower without him being aware. In contrast, GPS speed is very accurate and is independent of the motorcycle speed measurement. RR

A Motorcyclist’s 
Guide to the Galaxy: Satellite Navigation, Part 1Yuval Naveh
Back in the 80s I got hooked on motorcycles after reading 
great Round The World (RTW) adventures and following the stories of Paris-Dakar rallies. My first bike was an East German two-stroke 301cc MZ that for all purposes was an ADV bike before that category was invented. Luckily, today is the dawning of the age of ADVerius, and the Suzuki V-Strom DL650 is a natural choice for a ‘function-over-form’ guy like me.

Writing code started when I was child, on a Sinclair Spectrum computer with 48 KB RAM, and I haven’t stopped since then. When I’m not dreaming about riding or sailing around the world, or building electronics, I work as a chief technology officer (CTO) for a company specializing in financial crime prevention.

Text: Yuval Naveh
Photography: Yuval Naveh and Openclipart.org

Look for the next installment of Satellite Navigation in the 
Mar/Apr ’15 issue.

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