What is a reasonable timeout for acquiring a GPS fix?

Question

I am creating a BREW app that requests the user's position.

If the phone cannot acquire the position, I would like to display an error.

How long should I wait for my callback to be called before I determine that the phone is not likely to get a GPS fix?

Answer 1

When a cold start is required, the receiver has to download a full set of Ephemeris data, which is broadcast from the GPS satellite over a 30 second cycle and re-transmitted every 30 seconds.

So I would say that 60-90 seconds (two or three Ephemeris cycles) would be a suitable time to wait before declaring failure.

http://www.navigadget.com/index.php/gps-knowledge/ttff-time-to-first-fix

Note that if a device requires an almanac download, the startup time can be much longer (on the order of 12.5 to 15 minutes). This is referred to as a Factory TTFF (Time to First Fix).

Answer 2

I might go with an increment (say 20 or 30 seconds) between notifying the user that you have failed to establish a link, and give them the option to stop trying. Keep at it until they stop you, or a set number of iterations have passes (say 5 - 10 iterations).