Waiting for GPS Signal

[bondy99]

Hi,
Has anyone had this problem and what was done to resolve it?

Last week I used my TomTom device to travel more than 4 hours to a place I have never been to previously. The device worked until I stopped at a servo to fill up on fuel and have something to eat. My device would not restart. it remained frozen waiting for a valid gps signal. It stayed like that for 1 and half hours so I switched it off and used my smartphone using Google Maps. At least I had a working map to show me where I am and what routes to take.

After arriving at the destination. I stayed for an hour to pick up an item.

I switched the TomTom device back on, I switch it on and off a few times. then out of the blue it worked again.

After a few miles and still on the Toowoomba Bypass Range I had to stop the car, switched engine off for a comfort stop. I then switched engine on and switched the TomTom device back on, only to have the same thing happen "Waiting for valid GPS signal. I left the device on for at least 2 hours and drove 210klms and still never recovered so I switched it off.

Would this be a TomTom device battery problem or something else?

Thanks.

 

[Willy875]

Hello,
If this is for the XXL 540, as in your profile via TomTom Home, do you update the satellite positions with QuickGPSFix?

 

[bondy99]

Hello,
If this is for the XXL 540, as in your profile via TomTom Home, do you update the satellite positions with QuickGPSFix?

Yes, I have managed to get the latest map update. I'm certain I have updated with QuickGPSFix, but may have to do so again in case it never updated.

 

[canderson]

Yes, I have managed to get the latest map update. I'm certain I have updated with QuickGPSFix, but may have to do so again in case it never updated.

Map update and QuickGPSFix updates don't necessarily happen at the same time. Be sure you've updated the latter.

 

[Willy875]

@bondy99
You should update QuickGPSFix every 7 days.

 

[bondy99]

@ Willy875,
Ok. I thought the QuickGPSFix would last longer. Much appreciated.

 

[canderson]

Ephemeris data should be good for at least two weeks before satellite position drift starts making a noticeable difference.

It all comes down to two lines of numbers (aptly called a 'two line element set') for any given satellite that mathematically define its orbit, and how long the orbit is stable enough to be accurately defined by those two lines of numbers. Then some agency has to keep recomputing those values based upon actual orbital observations to keep the data up to date.

I've written a bit of code for this project that is responsible for steering these beasts:

United States Space Surveillance Network - Wikipedia

en.wikipedia.org

Take the word "Deep" with a very big grain of salt. They're only interested in things that circle the Earth.

 

[bondy99]

@ canderson, much appreciate the reasoning behind why it needs updating.

 

[canderson]

It's interesting. All kinds of external factors cause some amount of upset to 'regular' orbits. Even flying close to the Earth's two poles causes a change.

The effects of traveling over the poles—along with perturbations caused by Earth's shape, gravitational anomalies, and atmospheric drag—are mostly but not entirely deterministic. These forces, along with external influences such as the gravitational pull of the Moon and Sun, follow predictable patterns, but have to be accounted for on a regular basis, hence the need for the updated ephemeris (TLE) data.

The reason for all of this is that your device's position calculation is all done based upon its distance from the satellites being used for the calculation (and hence, the precise timing of signals reception), and knowing rather precisely where they are is the only way to know the exact distance at any given moment. When the satellites start to drift vs. their assumed position, the quality of the calculation is degraded. The device makes the assumption that you're on a road, so you don't often see that error appear on the device map. Only if the calculation gets really wonky will your position drift off-road and out into the weeds on the map.