Why is the blue accuracy circle 320 meters but the accuracy data field says 4meters?

[passdump]

As far as I can make out (from reading posts like here: http://forums.Groundspeak.com/GC/index.php...t&p=2643198 ) the blue circle denotes the GPSr’s accuracy estimate. On my GPSr the radius of the blue accuracy circle is 320 meters but the “accuracy” data field says its 4 meters. Whats going on there then? Why the huge difference between the two estimates?

[+Red90]

The circle shows combined accuracy of the GPS signal and the map data.

[Hertzog]

The circle shows combined accuracy of the GPS signal and the map data.

If the radius is 320 meters when the "accuracy" is 4 meteres, you are likely displaying the basemap; none of the more detailed mapsets add near this much to the circle radius.

[+dsshepard]

Could what you are seeing is the circle for the proximity alarm?

[passdump]

While testing out my GPSr I accidentally stumbled on something. I noticed that when I changed the map using the Map setup page of the GPSr I noticed that the blue accuracy circle also changed!

 

If I used the standard Americas base map that came pre-installed on my VentureCx then the accuracy circle would be in-or-around what the accuracy data field displayed. Fine.

 

If I then enabled the Garmin World base map (originally meant for the iQue 3600 but also works on the Venture Cx) then the accuracy circle would be stuck at around 320 meters, even though the accuracy data field would be way smaller, say 4 or 5 meters.

 

It’s strange that the map loaded should affect, what I would have thought was purely an internal calculation of the GPSr. Especially as the accuracy data field (thankfully) isn’t affected by the loaded map. Weird.

[CenTexDodger]

While testing out my GPSr I accidentally stumbled on something. I noticed that when I changed the map using the Map setup page of the GPSr I noticed that the blue accuracy circle also changed!

 

If I used the standard Americas base map that came pre-installed on my VentureCx then the accuracy circle would be in-or-around what the accuracy data field displayed. Fine.

 

If I then enabled the Garmin World base map (originally meant for the iQue 3600 but also works on the Venture Cx) then the accuracy circle would be stuck at around 320 meters, even though the accuracy data field would be way smaller, say 4 or 5 meters.

 

It’s strange that the map loaded should affect, what I would have thought was purely an internal calculation of the GPSr. Especially as the accuracy data field (thankfully) isn’t affected by the loaded map. Weird.

 

Garmin assumes that if you are close to a road thenyou are on the road. If the your actual position is on the road, but the map incorrectly has the road off, then the accuracy circle says that you are somewhere withing that circle.

[passdump]

Garmin assumes that if you are close to a road thenyou are on the road. If the your actual position is on the road, but the map incorrectly has the road off, then the accuracy circle says that you are somewhere withing that circle.

 

Ahh...ok. I think I have it. If there is a conflict between where the map "tells" the GPSr my location is and where the GPSr thinks it is, then the accuracy circle enlarges to cover the conflict area (?)

 

Thanks.

[+Red90]

As I explained above, it shows the combined accuracy of the GPS AND the map. The maps have a limit on their accuracy. The circle is to tell you that on THAT map you should be within the circle.