Saturday, January 09, 2010

The 350mph jogger

Anyone who was watching the track of G4ILO-12 this morning may have been surprised to see me whizzing along at 350 miles per hour over south-west Scotland at 10,000 feet.

No, I hadn't taken a trip by plane. I had APRSISCE running on my phone in its desktop cradle and when I noticed my icon scooting across the Scottish landscape I saw that the GPS was losing its position.

I don't know what caused this, but after it occurred I couldn't get the GPS to lock up again, even when using another application (Google Maps) and taking the phone outside in the garden to be sure it could see the satellites. I had a sinking feeling that the GPS in my phone had failed. Fortunately, after turning the phone completely off and then on the GPS started working properly again. It was certainly a worrying few minutes!


Lynn (D) said...

This seems to be a "feature" of the internal GPS inside HTC phones. My AT&T Tilt GPS does this when it stays too long in an area of marginal signals. It seems to decide that a single satellite is the ONLY one that is right and zings you 100s of miles away from where you really are.

Unfortunately, software like APRSISCE and Google Maps can only believe what the GPS is saying, even though people can tell it isn't right.

I've found 2 ways to get the GPS to finally give up on the lone (sometimes 2) satellite that is throwing it off. First, you can simply reboot your phone. I used to do that, but it gets old.

The better way is to turn off the GPS in ALL apps that might be using it (or close the app if there's no option to disable the GPS). Let it turned off (or closed) for 2-5 minutes then turn the GPS back on. In APRSISCE, if you still get a single green satellite on the top line (in use), it didn't work, turn it off again and wait longer. If you end up with 3+ satellites cooperating in the fix, I've always landed back where I belong.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile

PS. You'll see the same effect with Google Maps when you keep your phone's GPS out of coverage long enough, but we don't tend to let Google Maps open unless we're out and about. With APRSISCE, we tend to leave it running to see what's going on around us. I just make it a habit to toggle the GPS off (double-click the Fix Quality box) when I go indoors.

Unknown said...

Thanks for the comment, Lynn. I'm learning lots with this software. I didn't know I could turn the GPS off. I'll try and get into the habit of doing that when I'm here (and also try and remember to turn it back on again when I'm going somewhere!)

Tim said...

Incidentally, I get the same effect on iBCNU and iPhone. In that case, it is generally because you can't initially get a GPS fix (being inside or something) and so the phone works out an approximate location based on the cell tower it's seeing. Then it gets a GPS fix and the program says 'hey, I've moved!' and you get the rapid movement.

At least, I think that's what's happening!