Best accuracy with gpsmap 76csx

[Rick]

Hello,
Would anyone know which of the following would be the best way to get a more accurate point horizontally and vertically I am using a Garmin GPSmap 76csx?

1. Set the gps on the point and let it average for one hour or so.

2. Set the gps on the point, turn on the tracking mode set to one or two second interval, let it collect for an hour or so then average the collected points.

Any input will be appreciated,.

Thank you,
Rick

 

[kered]

Make sure WAAS is activated if it has it, this will give a better position

 

[Andrew Kalinowski]

To the best of my knowlege; Doing math (weighted average) on the data set obtained using the second method should give you more accurate results than depending on the averaging done by the receiver. The longer the session, the smaller the difference will be. At one hour, the difference may be insignificant.

 

[Rick]

Thank you very much for you're input I will try a few tests and re post the results.
Rick

 

[txrpls]

I can't speak for all hand held units, but in generalities there is no software on board that will average out the positions collected to get a better position solution. I think the only way it would work is that would have to average the shots externally. I doubt this will gain you anything, since you accuracy is still limited by the accuracy of the unit with WAAS on. You will never get sub-meter accuracy with the consumer units. With the survey grade units we use, we cannot get that accuracy without using differential positioning or post processing the data. On most survey grade receivers you can get a "better" position by letting the receiver "cook" on the point for a longer period of time. The position is still only accurate to 10-15 meters in true location. For new projects in an area with no control we generally do three 2 hours sessions at different times of the day and process the data with the NGS OPUS program. The best analogy I can offer is trying to get sub meter accuracy with a hand held is like trying to drill a 1/16 hole with a Black and Decker hammer drill. Hope this helps.

 

[Andrew Kalinowski]

Sorry to say it but your information is inaccurate.

Most of the handheld units have an averaging function and 76csx does have it. Ref. page 8 of the manual http://www8.garmin.com/manuals/GPSMAP76Cx_OwnersManual.pdf

As for the averaging, it's not that hard to get couple meters accuracy and often better with customer grade receivers ( http://users.erols.com/dlwilson/gpsavg.htm ) the problem is, one can not guarantee the solution so, it's not good for legal surveying but, IMHO it's perfectly fine for informal use.