TomTom GPS

Tony

It wouldn't start until well after 0900, it would stop repeatedly between then and 12.30, go awol for 90 minutes, and then it would only perform poorly until 9 minutes to 5 when it would shut down altogether.

Too true Bob.

Hi That's correct everytime I plug the unit ( Tom Tom One V3) in and open "TomTom Home" , then click check for updates it does updates for the G Fix everytime. I have been told that if you dont keep the update Up? the unit can lose it's accuracy.
Have been hearing of some units playing up in the Flinders , seems due to the ore bearing rocks,
Cheers Des.

Hi Des,

Just for clarification mate, whoever told you that is telling porkies.

The Tomtom will not lose accuracy.
GPSfix merely speeds up the process of locking on to the satellites as the device "knows" where to look first.

Instead of taking upto 20-30 secs to lock on, I find my Go 720 locks on within 10 secs or so.


Bill.

Before a GPS can establish its position, it needs to download Ephemeris data from at least 4 satellites - to do this it has to receive data from them for 30 seconds WITH NO INTERRUPTION. This can be difficult while driving under trees or near buildings.

All that Assisted GPS does is to download this info, while connected to the Internet to allow less waiting time before a fix.

Older GPS units never connect to the Internet and their accuracy never degrades.

Mike,

The newer Tomtom GPS units don't connect to the Internet either and therefore their accuracy also never degrades.

Only when the device is connected to a computer does it receive updates. TheTomtom Home application establishes a connection via the Internet to check for updates and if available, downloads them to the Navigation device.
Both GPSfix (satellite location info) and Map corrections are updated in this manner.


Interference from buildings, etc. will interrupt satellite reception on any GPS enabled device, but not technically degrade their accuracy. It simply stops tracking during such times.


Bill.

"newer Tomtom GPS units don't connect to the Internet either"

- I think people are aware that GPSs don't connect to the Internet, when connected to a PC that's conected to the Internet, they will update their data.


"Interference from buildings, etc. will interrupt satellite reception on any GPS enabled device, but not technically degrade their accuracy. It simply stops tracking during such times. "

No. Nearby buildings or trees will reduce the number of satellites that are received, and that will reduce accuracy of the fix long before you lose tracking completely.

Thanks Fella's, looks like we can still learn something everyday, thats what I like about this forum, always lots of helpfull advice,
Also as regards to the Flinders debate one of my mates works at Roxby and his garmin some times has brain fade ( his words) up there.but it doesn't last long,
Just one thing I have noticed my Tom Tom with lock onto the sats inside at my desk, but my Garmin760 will only lock on outside , but it will hold them when I come back in,???
Cheers Des.

GPS receivers vary greatly in their ability to pick up satellite signals.

When I started writing GPS software twenty years ago, the only affordable GPS receivers were ONE Channel - they had to step through the satellites they needed to receive. OK for planes and boats with no obstructions, useless when driving near trees.

Soon 4 channel receivers came out and these were usable for driving. I used them on commercial aircraft but only picked up satellites on your side of the sky - the receiver needed to be able to "see" the satellites.

When 12 channel receivers came out the difference was amazing - in a commercial flight it would pick up all sats above the horizon.

Then SiRF III came out and now you could walk under thick vegetation or in canyons and it would maintain lock. Bushwalkers Wilderness Rescue uses them to keep a tracklog of searches in very rugged rainforest terrain.

"my Garmin760 will only lock on outside , but it will hold them when I come back in,??? "

GPS receivers need to pick up Emphemeris Data for at least 4 satellites to get a fix and this means an uninterrupted signal for 30 seconds. Once it has Ephemeris, it only needs needs to pick up shorter transmissions for each fix.

So if your signal is weak indoors, it may lose lock every 10 seconds and therefore not be able to pick up Ephemeris.

If your GPS is having trouble getting lock while driving under trees or near buildings, you will get faster lock if you stop.

Hi Willem
I had some problems on Lake Torrens a couple of years back, but the situation only lasted for just over half an hour. I was later informed when I submitted my report that the Department of Defence were conduction GPS blocking activities at Woomera, and from other reports, these test are still happening to this day. They may not be launching many rockets there these days, but are still carrying out a lot of secret work.

Cheers

Stephen