HELP !

[iaing]

I'm currently on a ferry to Zeebrugge but on my way to the boat, my 2610 was showing the triangle for my position incorrectly. On screen it seemed to be about 1cm from the actual route I was on, although it did vary occassionally. There was also a circle round the position indicator.

I've not got my instructions with me - what's wrong and how do I change it back to reading correctly??

 

[Deleted account W]

Sounds like it's only using the base map and not the detailed mapping. Make sure you've got the right maps loaded and ticked in the Map Info section of settings

 

[iaing]

Surely I loaded the maps before I left.......!!

 

[Deleted account W]

Surely I loaded the maps before I left.......!!

Zoom out to 200miles and you should be able to see the map segments you have loaded as grids

 

[chasr]

I think the circle is showing that the GPS is unsure of its position. Stick with it when you arrive, and all should be well. Provided, that is, you loaded the maps.

 

[PanEuropean]

...There was also a circle round the position indicator...

Iain:

The circle around the vehicle position symbol indicates the level of confidence that the GPSR has in the position being displayed. There is a whole lot more to this than simply the quality of the satellite reception.

The major factors affecting the display of a circle around the position symbol are as follows:

1) The quality of the position fix that the GPSR has from observing the satellite constellation. You can determine the 'raw' accuracy of the position fix by going to the GPS settings page, and looking at the accuracy value displayed there. It will indicate something such as '17 feet' or similar - indicating that the satellite reception quality is such that the GPSR is confident that the position displayed as a latitude / longitude is accurate within 17 feet.

2) But, that is not all there is to it. Let's presume that the cartography for the map you are currently displaying has not been validated by Navteq - meaning, they have not driven that route themselves to confirm that the vector map depiction of the road / trail / ferry route is, in fact, dead accurate. In such a case, even though your GPSR might have a super-accurate lat / long position fix, the GPSR will display a circle around the vehicle position symbol because there is some uncertainty about whether the cartography you are looking at accurately depicts the position of the road / trail / ferry route.

In other words, the uncertainty can be caused by one of two factors (or a combination of the two) - poor satellite reception, or, the possibility that the underlying cartography may not depict the road / trail / ferry route with absolute precision.

In your case (on the ferry), I suspect it was the latter - uncertainty that the dotted line depicting the ferry route was, in fact, the exact path that the Captain of the ferry navigates - that resulted in the display of the circle. If you use WorldMap cartography, you often see the circle, even when you have perfect satellite reception with differential correction, such that your lat-long position is known to be accurate within 1 centimeter. It's no comfort to you that your lat/long position is deadly accurate if the cartography you are viewing is not equally accurate - hence the display of the 'uncertainty circle'.

Michael

 

[markie_wales]

one other thing

I'm currently on a ferry to Zeebrugge but on my way to the boat, my 2610 was showing the triangle for my position incorrectly. On screen it seemed to be about 1cm from the actual route I was on, although it did vary occassionally. There was also a circle round the position indicator.

When you say "1 cm from route" you don't say at what zoom level that is, so, it may not be far off (when the circle is displayed).

I can't remmeber exactly what it's called, but isn't there a "snap to road" option, where the triangle will "snap" to the nearest road? No idea whre in the menus it is (if it is not just a mental breakdown, and this option does actually exist !!).

Mark

 

[Deleted account W]

I can't remmeber exactly what it's called, but isn't there a "snap to road" option, where the triangle will "snap" to the nearest road? No idea whre in the menus it is (if it is not just a mental breakdown, and this option does actually exist !!).

Mark

Yes "snap to road" won't work on the basemap which is why I think the units only using that.

It's happened to me before

 

[PanEuropean]

You will sometimes see the accuracy circle appear even under the following conditions:

1) Great satellite reception,
2) Detailed cartography installed,
3) Snap to road enabled.

If there is too much of a difference between where the GPSR determines that it is (from the satellite signals), and where the cartography shows that the road is (from the maps you have loaded), and the hidden attributes for that road do not indicate that the position of the road has been independently verified, the GPSR will show you on the road, but it will pop up an accuracy circle just as a 'head's up' warning to you that not everything matches up properly. The implication here is that if you are looking for a side road that branches off from the road you are presently on, it might not appear exactly where the cartography depicts it.

This is a very thoughtful and helpful feature when you are navigating in rural areas.

Michael

 

[Fanum]

You will sometimes see the accuracy circle appear even under the following conditions:

1) Great satellite reception,
2) Detailed cartography installed,
3) Snap to road enabled.
4) When the Americans turn down the signal strength just prior to launching a precision bombing raid on the area



Michael