GPS adrift again?

Andy_P · Posted: Wed Oct 01, 2008 3:04 pm Post subject: GPS adrift again?

Over the last couple of days I have been seeing the problem again where the TT believes it is about 100-200 yards away from its true location.
This time it's NORTH by a 100 yards or so.

Sometimes it's difficult to spot (especially if you have a route entered) because of the way it "snaps" onto the nearest road, but you can see it if there is a road parallel to yours in the appropriate direction so the TT sits on the wrong one.

When it has happened before, it has been noticed by several other people at the same time.
Anyone?

dhn · Posted: Wed Oct 01, 2008 5:56 pm Post subject:

Andy, have you ever found doing a pin reset help the situation at all?
_________________
David

imokah · Occasional Visitor Joined: Jun 13, 2008 Posts: 1

Hey guys...my GO720 did this twice on me this week while driving in western Colorado. I was traveling on State Route 50 and the next thing that I am watching is the pointer veering off on a cow trail. The 720 NA map has some weird roads showing that are nothing more then ancient hay wagon roads through cattle country. Pointer did snap to the correct route, but it was interesting watching where that pointer was trying to go.

Andy_P · Posted: Thu Oct 02, 2008 1:05 am Post subject:

Snudge · Posted: Thu Oct 02, 2008 1:31 am Post subject:

Andy, I think it was you who previously blamed the 'quickfix' data for that effect - so can you relate what you are seeing now to a recent quickfix update?

Andy_P · Posted: Thu Oct 02, 2008 1:46 am Post subject:

Yes, I had got a GPSQuickfix when I first tried Home v2.4

Darren · Posted: Thu Oct 02, 2008 8:05 am Post subject:

I avoid QuickFIX as much as possible, it's simply not necessary for most devices.
_________________
Darren Griffin

rover220 · Regular Visitor Joined: Jul 18, 2006 Posts: 63

mines done this ever since upgrading from 7.whatever to 8.010

does usually settle down after a while but its a right pain.

Andy_P · Posted: Thu Oct 02, 2008 12:31 pm Post subject:

I'm still on v7.221, so it isn't a software version issue.

What I need to do is lug a laptop around with me so I can delete the Quickfix files WHEN IT'S DOING IT, rather than later that evening.
That's the only way I can see that I can really convince myself they are the cause.

theripper · Posted: Thu Oct 02, 2008 3:05 pm Post subject:

Is it possible that this is map related as on numerous occasions when driving between Christchurch and Lymington(around Everton) although I am on the main road both TT and my old laptop with R66 show mee driving throuth the village.

theripper

Andy_P · Posted: Thu Oct 02, 2008 4:20 pm Post subject:

Surely if it was a map error, it would be in one place and would happen all the time.

This is on routes I do every day and all across London.

StanStill · Regular Visitor Joined: Feb 27, 2005 Posts: 81

As I said in a prvious post, I am sure that I have heard somewhere that solar activity distorts the upper atmosphere so that signals to and from satellites are pushed out of position, thats why sometimes the signal to your satnav shows you in a slightly different position and why your satnav cannot find the satellite to lock onto even though it has the correct position from quickgps fix.

If it was a problem with quickgps fix all that would happen is that the TomTom would be looking in the wrong part of the sky and it would just take longer to get a fix on the satellites, it would not affect the signal from the satellite to your TomTom.

Andy_P · Posted: Thu Oct 02, 2008 4:51 pm Post subject:

I should have mentioned... while this is happening I have perfectly good satellite reception (as shown by both the signal strength meter on the status bar and by the fuller display on the GPS status screen.
So it is not lack of satellite lock.

I do not pretend to understand why adding a GPSQuickFix patch should do this (obviously it shouldn't!) and I know that all it is supposed to do is give thesystem a "place to look".
BUT it happens and all I and others can say is that it TENDS to happen soon after a QuickFix download.

StanStill · Regular Visitor Joined: Feb 27, 2005 Posts: 81

You may have a good satellite lock but if the returning time signal from the satellite is bent from a straight line (like the way the image of a stick in water is bent when the light goes through the water) the timing signal will be slightly wrong and show you in a false position.

I am not an expert in these matters but it seems to me to be the most logical explanation as I had this problem very occasionally with the original Go - well before quickgps fix.

But then again, as my wife keeps telling me, I could be wrong. CoPilot

Andy_P · Posted: Thu Oct 02, 2008 5:59 pm Post subject:

Thanks, that makes a lot more sense. Smile

Anyone else seeing it at the moment though?

	PocketGPS
	Web