Your smartphone downloads ephemeris data everyday. What does it do?

Every day your smartphone is downloading ephemeris data. But it's not just your smartphone, your tablet is, your car's navigation is too, every device in the world with a GPS is downloading ephemeris data. So what is ephemeris data, and what does it do for you?

Ephemeris data is...

Ephemeris data is a collection of numerical values that can be used to determine the location of a satellite that is orbiting the Earth. Each satellite has its own unique collection of numerical values to determine its location.

Great, but how does it help me?

When you start up Google Maps or want to tag a location for your Instagram post, how quickly do you expect your smartphone to determine your location?

Instantly, right?

One of the key reason your smartphone is able to locate you instantly is the use of Ephemeris data. (Another key reason is WiFi and cellular positioning, which I will cover in another article).

Ephemeris data, when supplied to a GPS device, ensures you get the quickest and most accurate location possible.

The Technical Stuff

There are 32 GPS satellites orbiting around the Earth. At any given time only 8 to 12 satellites will be above you and visible to your GPS. For your smartphone, tablet, or car to determine where you are, the GPS must locate at least 4 satellites. With Ephemeris data, the GPS is aware of where all the satellites are around the Earth and can select the four best satellites to use to determine your location.

Why does it have to be downloaded daily?

Accuracy! The location of a satellite is affected by factors such as the gravitation pull of the Sun and the Moon to how accurate the onboard clocks are. All these factors make it difficult to have Ephemeris data accurately determine the location of a satellite for longer than a couple hours (There are a few expectations such as Predicted Ephemeris that can provide 14 days of Ephemeris data). Therefore for your GPS to work it's best, Ephemeris data needs to be downloaded and readily available to be used by the GPS.

Ephemeris data can be downloaded directly from the satellite, but this is slow and limited to getting Ephemeris data for visible satellites only. It is far more common to down a complete set of Ephemeris data either from the network provider or device manufacturer.

Ephemeris data is used to determine the exact location of a satellite orbiting Earth. Ephemeris data is downloaded daily to ensure your smartphone, tablet, and car obtains the quickest and most accurate location.


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