Factors that Affect GPS Accuracy

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. 

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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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Satellite Image Quality

18Birdies relies on the Google Maps system to provide the satellite images golfers see in the app. Ultimately, we are at the mercy of Google for the quality of the images and the frequency of the image updates. If the provided satellite images are outdated significantly enough that the image is unusable, we may disable the GPS satellite image view in the app.

Contrary to popular belief, Google does not have their own satellites for Google Maps image purposes. Rather, Google purchases satellite images from a number of different satellite image providers. Aside from Google itself, the factors Google uses to determine what images to buy is unknown. We can assume these factors may include...

• Just like all businesses, price and cost of acquiring the images is likely a factor considered by Google.
• Google services or business may update an area based on business, or future business needs and interests.
• Similar to price, the quality of the images is a factor that must be considered by Google as they ensure the highest leverl of service possible.
• Population or business density, including new construction or roads, may gain enough interest from Google that would require an update in the Google Maps system.

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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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