Averaged coordinates seem less accurate

[+hobgoblinkiteflier]

On a few occasions I have noticed that the coordinates that I get using the averaging function seem to be less accurate than if I just simply mark a waypoint. For example, the for last cache I hid, I averaged the coordinates on three separate occasions for about 5 minutes each time.

 

The second finder commented that the coords were off, so I checked and sure enough they were about 8 metres out. When I recorded the coords, the Oregon 450 was reporting 4-5metre accuracy, so I expected it to have averaged to something better than this. I marked a couple of waypoints, one either side but close to the tree where the cache was hidden. Then again tonight I took a couple more readings. The average of these is 0.005' North the 15minutes of auto-averaging figures.

 

Has anyone else seen this kind of problem? I think I might forget about the averaging function and just take a few standard waypoints on different days, letting the GPS settle each time.

[+luvvinbird]

On a few occasions I have noticed that the coordinates that I get using the averaging function seem to be less accurate than if I just simply mark a waypoint. For example, the for last cache I hid, I averaged the coordinates on three separate occasions for about 5 minutes each time.

 

The second finder commented that the coords were off, so I checked and sure enough they were about 8 metres out. When I recorded the coords, the Oregon 450 was reporting 4-5metre accuracy, so I expected it to have averaged to something better than this. I marked a couple of waypoints, one either side but close to the tree where the cache was hidden. Then again tonight I took a couple more readings. The average of these is 0.005' North the 15minutes of auto-averaging figures.

 

Has anyone else seen this kind of problem? I think I might forget about the averaging function and just take a few standard waypoints on different days, letting the GPS settle each time.

I do think it's important to strive for accuracy. I've used my Oregon 450's averaging feature too, but I still like to walk away 100 feet or so and then follow the averaged coordinates back to GZ. I'll do that a couple of times from different directions and then tweak the numbers until I'm satisfied with the results. I think we all realize that within 30-ish feet of the cache is acceptable but I'm always impressed by CO's who have me literally standing in front of the container.

[+ecanderson]

Quick waypoint averaging only deals with a certain set of inaccuracies. One thing it won't help enough with is a lousy HDOP that is caused when the satellite constellation just isn't in a good position at the moment. For that reason, it's a good idea to recheck at another time, after the satellites have had time to shift around a bit, to be certain that the average itself is stable.

Edited November 12, 2013 by ecanderson

[+BAMBOOZLE]

On a few occasions I have noticed that the coordinates that I get using the averaging function seem to be less accurate than if I just simply mark a waypoint. For example, the for last cache I hid, I averaged the coordinates on three separate occasions for about 5 minutes each time.

 

The second finder commented that the coords were off, so I checked and sure enough they were about 8 metres out. When I recorded the coords, the Oregon 450 was reporting 4-5metre accuracy, so I expected it to have averaged to something better than this. I marked a couple of waypoints, one either side but close to the tree where the cache was hidden. Then again tonight I took a couple more readings. The average of these is 0.005' North the 15minutes of auto-averaging figures.

 

Has anyone else seen this kind of problem? I think I might forget about the averaging function and just take a few standard waypoints on different days, letting the GPS settle each time.

I do think it's important to strive for accuracy. I've used my Oregon 450's averaging feature too, but I still like to walk away 100 feet or so and then follow the averaged coordinates back to GZ. I'll do that a couple of times from different directions and then tweak the numbers until I'm satisfied with the results. I think we all realize that within 30-ish feet of the cache is acceptable but I'm always impressed by CO's who have me literally standing in front of the container.

 

I totally agree....the number of caches I hit my head on are amazing.

Regarding accuracy and averaging the newer , higher sensitivity units are amazing. On the 450 and especially the 62S it is very rare for either the N or W to change over .001 from the time I start averaging through 2 or 3 minutes...its almost as if there is no averaging going on because there was such a good lock at the beginning. On older units you could see more N and W fluctuation as the units averaged.

[yogazoo]

As has been mentioned, precision is only as good as the DOP (dilution of precision) at the exact time of data recording. Accuracy is a different animal. The unit might be averaging a point as accurately as the signals allow but the precision is only as good as the ionosphere allows. GPS signals have good days and bad days, good hours and bad hours. You can forecast your DOP by visiting this link and downloading Trimble's free planning software. Be sure to set it up according to your location. Try going out to GZ and averaging coordinates when the DOP is predicted to be at it's lowest. Your precision will, in theory, be higher. It's also fun to see how GLONASS sats effect DOP. At my location GLONASS appears to help reduce DOP by a considerable amount.

 

LINK:http://trimble.dk/planningsoftware_ts.asp

 

An average of points is almost always more reliable than a single snapshot. Many scientists live by mantra "replicate, replicate, replicate". The more samples of data the more reliable the outcome.

 

Good luck

Edited November 12, 2013 by yogazoo

[Grasscatcher]

@yogazoo,

Did you know that there is an online version of that Trimble program now?

Don't have to install and keep up with the almanac updates anymore.

Works great.

[yogazoo]

@yogazoo,

Did you know that there is an online version of that Trimble program now?

Don't have to install and keep up with the almanac updates anymore.

Works great.

 

Whoa! I didn't know there's an online version. Sweet, thanks Grasscatcher! I use the program all the time to plan my data acquisition and your right, keeping up with almanacs can be a pain (but ultimately has been worth it). What would we do without the internets?

 

Link to the only online predictor I could find: http://satpredictor.navcomtech.com/

 

If there's another please post link. Thanks.

Edited November 13, 2013 by yogazoo

[Fangamon]

Interesting discussion of GLONASS here https://sites.google.com/site/gnssgofor/gnss

 

Basically switch GLONASS on if you have it

 

Even for us Australians down in the southern hemisphere? Surely not.

 

[+hobgoblinkiteflier]

Thanks for the interesting replies. The website with the DOP predictions might be useful. You could even check back later and see if you happened to pick a bad time to mark a waypoint, or it could be a good excuse for a DNF.

 

I think I will try some experiments in my back yard and see if I can replicate the odd behaviour I was reporting.

[+GeoTrekker26]

Yep ... GLONASS has provided full global coverage since end of 2011

 

More info here http://gpsworld.com/directions-2013-glonass-today-and-tomorrow/

 

Yup, it's real hard to design a satellite orbit that doesn't cover the southern hemisphere!

 

(for the humor or science impaired replace "real hard" with impossible)

[gpsblake]

Has anyone else seen this kind of problem? I think I might forget about the averaging function and just take a few standard waypoints on different days, letting the GPS settle each time.

 

I also noticed that using ADJUSTED benchmarks as a test. I think what might be happening is let's say your unit is accurate 80% of the time but floats out to 20-30 feet 20% of the time. Therefore if you average out the coords, it will be off by 5-10 feet because it's averaging all the coords when though your unit will most of the time be very accurate. As others have said, taking readings a few different times at different time of the day will probably help with accuracy.

[+GeoTrekker26]

Has anyone else seen this kind of problem? I think I might forget about the averaging function and just take a few standard waypoints on different days, letting the GPS settle each time.

 

I also noticed that using ADJUSTED benchmarks as a test. I think what might be happening is let's say your unit is accurate 80% of the time but floats out to 20-30 feet 20% of the time. Therefore if you average out the coords, it will be off by 5-10 feet because it's averaging all the coords when though your unit will most of the time be very accurate. As others have said, taking readings a few different times at different time of the day will probably help with accuracy.

 

Why at different times of the day? The satellite constellation is never the same at a given time on different days.

[yogazoo]

I also noticed that using ADJUSTED benchmarks as a test. I think what might be happening is let's say your unit is accurate 80% of the time but floats out to 20-30 feet 20% of the time. Therefore if you average out the coords, it will be off by 5-10 feet because it's averaging all the coords when though your unit will most of the time be very accurate. As others have said, taking readings a few different times at different time of the day will probably help with accuracy.

 

Why at different times of the day? The satellite constellation is never the same at a given time on different days.

 

gpsblake didn't say to do it on different days. He said to average coords at different times over a single day. But the key to really bumping the accuracy of any given point is to take several different readings over the course of a few days anyway. Or at a minimum of 90 minute intervals. The more samplings the better. Although it's always horseshoes and hand grenades.

[+GeoTrekker26]

I also noticed that using ADJUSTED benchmarks as a test. I think what might be happening is let's say your unit is accurate 80% of the time but floats out to 20-30 feet 20% of the time. Therefore if you average out the coords, it will be off by 5-10 feet because it's averaging all the coords when though your unit will most of the time be very accurate. As others have said, taking readings a few different times at different time of the day will probably help with accuracy.

 

Why at different times of the day? The satellite constellation is never the same at a given time on different days.

 

gpsblake didn't say to do it on different days. He said to average coords at different times over a single day. But the key to really bumping the accuracy of any given point is to take several different readings over the course of a few days anyway. Or at a minimum of 90 minute intervals. The more samplings the better. Although it's always horseshoes and hand grenades.

 

Yea, I misread that. I fully agree with the last statement. :-)

[+L0ne.R]

On a few occasions I have noticed that the coordinates that I get using the averaging function seem to be less accurate than if I just simply mark a waypoint. For example, the for last cache I hid, I averaged the coordinates on three separate occasions for about 5 minutes each time.

 

The second finder commented that the coords were off, so I checked and sure enough they were about 8 metres out. When I recorded the coords, the Oregon 450 was reporting 4-5metre accuracy, so I expected it to have averaged to something better than this. I marked a couple of waypoints, one either side but close to the tree where the cache was hidden. Then again tonight I took a couple more readings. The average of these is 0.005' North the 15minutes of auto-averaging figures.

 

Has anyone else seen this kind of problem? I think I might forget about the averaging function and just take a few standard waypoints on different days, letting the GPS settle each time.

 

I have had the same problem with my 62S. (Never had a problem with my 60Cx).

Edited November 18, 2013 by L0ne R