POI's Have Gone Off Road

sturgi · Occasional Visitor Joined: Dec 28, 2006 Posts: 55

Currently running a 720 with 815 Maps and 8.302 but have noticed since updating to 8.302 that the POI's I show all appear to be off road. I only show Petrol Stations and Car Parks along with Speed Cameras. The icon is in the right spot along the road but appears to show further Right on the screen so Petrol Stations are either in a field or down a side road.

Any ideas?

Cheers

Ian

PaulB2005 · Posted: Tue Mar 10, 2009 12:36 pm Post subject:

Who's POIs? TomTom or PGPSW?

sturgi · Occasional Visitor Joined: Dec 28, 2006 Posts: 55

Sorry TomTom's POI's except speed cameras wich are PGSPW's

Andy_P · Posted: Tue Mar 10, 2009 1:21 pm Post subject:

I suspect this is a recurrence of an old and as yet unsolved problem (it usually goes away by itself)
As you may know, most SatNavs for cars, "snap" your indicated position to the nearest road, so you cannot see any small positional errors.
There have been several incidents where this error gets large enough for the position of your car cursor to run about 100-200metres adrift, either ahead or behind your real position (if the road runs in that direction) or PARALLEL to the road. Often you only see it if there happens to be another road running beside the one you are on.

Once, about a year ago, I saw just what you are describing, but with some speed camera positions from this site. I didn't manage to get a screen grab at the time, but I made a mockup of what it looked like, and even still have it!

The general problem has been discussed on these forums several times (try a search for "200 yards" or "200 metres") but it has been one of the few "unsolved mysteries" that we have never really got a solution for.
I suffered with it fairly often for a while, (even convincing myself it happened at the same time on the same day of the week!) but haven't had it for ages. For a while we also convinced ourselves it was something to do with the GPSQuickFix downloads from TomTom.

For me, the situation usually slowly improved over 45 minutes to an hour, except for once when it persisted for about 5 days. Just when I had given up on it and was about to send it away for repair, it all came good, and hasn't shown the same symptoms for months since.

Pocketgps · Posted: Tue Mar 10, 2009 1:29 pm Post subject:

This reminds me that I use to create scenery for Microsoft's flight sim.

On each new release they use to move the position of the land on the earth - What power they have. It made it really difficult to keep moving the scenery to the new position, with some 1200 lats and longs to retype in and re-compile for it to work.

layingback · Regular Visitor Joined: Feb 12, 2009 Posts: 124

In the image posted you only have probably 3 satellites. That's marginal. In theory 3's enough, 4 to give height. But the 3 signals have to be perfect. Given that modern GPS chips can pull in 8 or 9 pretty easily with TT-sized antennas, chances are that if it could only latch onto to 3, then all 3 feeds weren't perfect. Accuracy is v. poor without extra satellites to compensate for momentary loss of 3rd sat (buildings or wet leaves overhead). An accelerometer and gyro could fix, but we can't all afford that model Wink

And as you say, the snap-to covers lots of sins, e.g. the road may well be in a different place from when the POI was added. POI location would most probably have been done on the highest quality map on a workstation, but a recent TomTom is a very compressed map. Amazingly so.

Lot better than when SA was on: 100m was considered good then, and the cursor on the road - without snap-to - a fluke! Frontage roads along freeways, as are common in some cities in California, would often lead to amazing directions as it tried to re-route off the freeway in order to get on it, if you see what I mean!

OADT, who at TT had the bright idea to make QuickIcons coloured? (See the green arrow jukebox/FM button in Andy's image.) They should surely be silhouette ones like the + and - ones in the corners. Laughing

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Andy_P · Posted: Wed Mar 11, 2009 2:26 am Post subject:

Faucet · Posted: Wed Mar 11, 2009 9:11 pm Post subject:

Just a thought.

This displacement of the map from the gps position as shown on Andy-P's mock up looks like what used to happen with Palm Top Software (which later became Tom Tom) running on the Psion 5. On that software there was a control to calibrate the map so that the curser was moved to the correct position.

I wonder if the error you are seeing is due to the software not calibrating correctly at start up, maybe moving off before having a fix?

On page 7 of the manual it says
The following conditions are required for successful calibration:
Your Go is receiving a strong GPS signal.
The car has been stationary for at least 5 seconds and then travels along a straight and level section of road for at least one minute.
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layingback · Regular Visitor Joined: Feb 12, 2009 Posts: 124

Most of the Page 7 quote is correct, but this is the first I've ever heard of

trevor.dowle · Lifetime Member Joined: 16/06/2003 05:22:14 Posts: 412

Andy_P · Posted: Thu Mar 12, 2009 12:59 am Post subject:

Pocketgps · Posted: Thu Mar 12, 2009 1:51 pm Post subject:

Andy_P · Posted: Thu Mar 12, 2009 3:08 pm Post subject:

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