I have just found out about the ee update file for AGPS, from what I understood needed to have a faster GPS synchronization - only lasting for a week.

I am actually wonder what type of information is contained in this file, and if it would be readable by any means on a pc.

Also, I am surprised about the fact that it expires. What is the reasoning behind that?

Thank you in advance!


In a nutshell1 AGPS (Assisted/Augmented GPS) is a method to help a GPS device determine the position of the GPS satellites by supplying pre-computed data. The data itself changes in time due to the fact that the satellites themselves change in position over time in a manner that can't be expressed by a simple formula directly implemented by the GPS device itself. Which explains why the data expires over time.

In lieu of using the pre-computed data, the GPS device can receive the equivalent data from the satellites themselves. However this data is only transmitted at about 50 bits/second, or about 6 characters per second. Thus with no AGPS data, the GPS device needs to accumulate enough data from the visible satellites to "fill in the blanks" when calculating a GPS position - which takes time.

If you shut off a GPS device and then turn it on again after moving it it a significant distance (or keep it in the same spot but turned off for a significant time), the required data needs to be refreshed. Providing AGPS data minimizes the time needed to acquire a GPS fix.

I just downloaded an ee file (130k in size) from Nikon and took a look at it. It appears to be binary data. Given the size and format I doubt there is any practical use for looking at it on a computer.

  1. I'm not a GPS engineer nor did I play one on TV or stay in a specific brand of hotel last night. This is just my general understanding on how things work.

This file contain orbits of GPS satellites (simplified). This information is required to calculate the satellites position and with precise time received from satellites to calculate your geographic coordinates. And it is indeed limited to one week data.

If you do not update this file you need to switch on you camera and stay in open space with good visibility to the sky and wait between 6 and 12 minutes to receive this data via satellite link data. But in this case this information will be limited to day or so.

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