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Fitness Trackers and Sports Watches with GPS
Crazy about accurately tracked pace, distance and route? There is no better way, as to use a fitness tracker or sports watch with build-in GPS. Wearables without GPS rely on the number of steps and the average distance of one step for a person of your age, body height and sex.
Though this approach seems fair, there are a lot of people that do not conform to the average value. Thus the results may vary considerably. Fortunately the size and costs of GPS chips have been reduced over the years, so that even wearables for beginners offer GPS functionality.
With build-in GPS you don’t have to take your smartphone with you in order to track the pace, distance and route. This list shows all the fitness trackers and sports watches that have build-in GPS.
To understand how distance and pace are measured, it is important to understand how a GPS device can locate your position by receiving the GPS signal.
Finding your position
The Global Positioning System – or short GPS – is a system of 30 satellites that orbit the earth at about 20,000 kilometer height. The reason for using so many satellites can be described best, when describing the purpose of just one satellite first.
Each satellite consists of an atomic clock and is broadcasting its position along with the atomic clock’s time to earth continuously. When received by a GPS device, the device can calculate the distance between itself and the satellite based on how long it took the signal to arrive on earth.
Positioning using GPS
For convenience, let’s consider the earth that you are standing on is flat. The mechanisms for locating a position on a sphere are the same, but not necessary for getting the basic idea.
Let’s get back to the distance between you and a satellite. Once you have the distance you can be sure to be somewhere on a circle that is the intersection of our “flat” earth and the sphere with its radius being the distance between you and the satellite.
This applies for the distance derived from a second satellite as well. Most likely the distance between you and the satellite will differ from the first, i.e. you can be pretty sure to be somewhere on a second circle and that circle being the intersection of the “distance sphere” and the “flat” earth.
As your position is somewhere located on the first circle and at the same time is somewhere located on the second circle they must have something in common – they intersect.
When two circles intersect, they do so in two points. Given this information you can be sure that your location is either the first or the second intersection.
A third satellite is needed to give you the missing piece of information. The whole process is called trilateration and as you can see it requires at least three satellites. With more satellites used resulting in a more precise result.
Now it becomes obvious why so many satellites are needed: If one satellite sets behind the horizon, another satellite must appear above the horizon. To ensure that at least four satellites are “visible”, they a distribute in a smart manner around the earth.
Tracking of pace, distance and route
To track the pace, distance and route, the GPS device has to locate your position continuously and calculate the distance between two adjacent positions. A short interval between two trilaterations allows for greater accurancy.
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