Factors that Affect GPS Accuracy

In This Article

The Basics
Not Enough Satellites
Satellite Position
GPS Drift
Lost GPS Signal
Multipath Error
Signal Obstruction

The Basics

GPS, whether it is a mobile phone or a standalone GPS device, requires a variety of factors to determine and display accurate location.

If you are experiencing issues with GPS accuracy, please see some potential reasoning below.

Please keep in mind that most of these are outside of the control of 18Birdies, but if you are experiencing GPS issues, it is always a safe bet to contact us at Support@18Birdies.com so our team of esteemed support members can investigate further.

It is important to know the difference between the Global Positioning System (GPS) and Global Navigation Satellite System (GNSS). GNSS is the general name for a satellite system that is used to pinpoint the geographic location of a user's receiver anywhere in the world.

There are three major GNSS systems currently in operation; the United States' Global Positioning System (GPS) and the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS) and Europes Galileo system. 

Satellites

Not Enough Satellites

GPS devices, whether it is a mobile/phone device or a standalone GPS device, all use a number of satellites in orbit above Earth in order to make a determination on your estimated location.

A minimum of four (4) satellites are required to be in-line-of-sight in order to give the roughest estimation of location. Any amount of satellites less than four will return an error message 'GPS Coordinates Not Available'. The more satellites that can be seen and used to provide readings, the more triangulation points & references are obtained.

Generally, 7 to 8 satellites are preferred in order to calculate and display a location within 10 - 11 yards.

Satellite Position

Now that we have addressed the number of satellites required to provide location, it is important to mention that the actual position of the satellites providing the location makes a huge impact on accuracy and functionality.

Generally, a set of satellites that are dispersed across a larger area of the sky will return a much more accurate and precise location.

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Location and Device

GPS drift 

The GPS track deviates from the road. You may see that the route generally follows the shape of the road but with much less precision.

This can be caused by reflections and shadowing on an image.

Lost GPS signal 

If the GPS signal is lost and sometime later re-acquired the pre- and post-signal-loss points will be treated just like any other two points (although more time has elapsed between them) and connect them with a straight line.

Multipath Error

A 'jumpy' GPS track can cause your activity to report more distance than you actually traveled since each 'zig' and 'zag' of your GPS track has to be accounted for with a straight line connecting them.

This specific issue can be caused by having local obstructions that cause the GPS signal to bounce off of, which sends varying location details to your device. This can result in instability of your location.

Signal Obstruction

Buildings, trees, tunnels, mountains, clothing, and the human body can prevent GPS signals from the satellites reaching the receiver. When possible, put a GPS receiver in a place where it has a clear and unobstructed view of a large portion of the sky.

In some cases, this can be done by holding the GPS device in a back pocket, or on the outside pocket of a backpack, or in a handlebar mount. In other cases, the obstructions are unavoidable, like in downtown areas where tall buildings block the view of the sky, or when in dense trees.

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