GPS accuracy

[Guest Keon]

First (registered) post!

 

I had "bookmarked" my house on my eTrex and when coming back from a trip, the GPS pointes 10m away from the place I stored earlier. I know that this is probably the limit of my cheap eTrex but can I improve waypoint accuracy by standing still for 5 minutes and THEN storing the coordinates? Does the GPS-receiver gets a more precise reading after a while?

 

------------------

ELEV: 40m

N 050°56.025'

E 005°25.995'

[Guest sar6cm]

Howdy,

I have owned several Garmin gps,and two Etrex units. I have just a few thoughts about the difference in your bookmark and position...

DOP may have a lot to do with the difference, to include the difference between the time you set the waypoint and the time you returned. As for 10meters, that is not unusual if accuracy is, say 15meters. I have been very pleased with return point accuracy with Garmin.

 

Hope this helps a little.

[Guest swangner]

The theoretical accuracy of the entire GPS system is 15 meters, so your 10 meter result is well within this range. Actually, returning to a waypoint involves 30 meter inaccuracy - 15m when setting it originally, and 15m when returning - so you're doing well with 10m. BTW, this is a limitation of the GPS system, not the receiver.

 

After you've used the unit for a while, you'll see that many times you can get accuracy better than 15m, but never count on it. The eTrex (and most other consumer GPS receivers) are rated at 15m accuracy.

[Guest cyclone]

actually, from what I learned a few years ago part of the accuracy involves errors from one GPS unit to another. For instance, I you are given a set of coordinates derived from another GPS unit, the 15m figure applies. However if you mark a location with your GPS, you should be able to return to that waypoint with somewhat greater accuracy.

[Guest Kickaha Ota]

I'm not familiar with the eTrex; but the eMap does have the option to improve the accuracy of waypoints by standing still for a long time. While creating a waypoint, or while viewing the details of an existing waypoint, press Menu; a menu will pop up with an "Average Location" option. When you choose that option, the eMap will start repeatedly taking location readings and averaging them together; it will also show you the estimated accuracy of the readings it's taken so far. If you're willing to stand still for an hour or so, you can make a waypoint that's accurate to within a meter or two.

 

Of course, this doesn't mean that you'll be able to return to the waypoint with perfect accuracy. The waypoint itself may be dead-on; but when you return, you'll still have to deal with the fact that the reading of your current location is only accurate to within about 15 meters, unless you're willing to stand still for another hour. Still, as another poster mentioned, you're effectively cutting the potential inaccuracy in half--since you now only have to deal with uncertainty about your current location, not with uncertainty about both your current location and the waypoint's coordinates.

 

If you're planting a cache somewhere, you should definitely use this feature when creating a waypoint for the cache's location, assuming that standing there for an hour won't get you arrested for vagrancy.

[Guest Kickaha Ota]

I'm not familiar with the eTrex; but the eMap does have the option to improve the accuracy of waypoints by standing still for a long time. While creating a waypoint, or while viewing the details of an existing waypoint, press Menu; a menu will pop up with an "Average Location" option. When you choose that option, the eMap will start repeatedly taking location readings and averaging them together; it will also show you the estimated accuracy of the readings it's taken so far. If you're willing to stand still for an hour or so, you can make a waypoint that's accurate to within a meter or two.

 

Of course, this doesn't mean that you'll be able to return to the waypoint with perfect accuracy. The waypoint itself may be dead-on; but when you return, you'll still have to deal with the fact that the reading of your current location is only accurate to within about 15 meters, unless you're willing to stand still for another hour. Still, as another poster mentioned, you're effectively cutting the potential inaccuracy in half--since you now only have to deal with uncertainty about your current location, not with uncertainty about both your current location and the waypoint's coordinates.

 

If you're planting a cache somewhere, you should definitely use this feature when creating a waypoint for the cache's location, assuming that standing there for an hour won't get you arrested for vagrancy.