eTrex 30 Waypoint Averaging

[+MinionBrigade]

Looking for help using the Waypoint Averaging feature on my eTrex 30. I have placed a few caches, including one multi, using this feature. I follow the directions in the manual, but the accuracy is not consistent. Some of my coordinates still seem to be off. Does anyone have experience with this? How many "samples" do you take of the coordinates; the manual implies that only one is necessary as long as the Sample Confidence is at 100%. I'm starting to think this is not correct. I know that the coordinates are good within only 20 feet or so of GZ, but i'm getting negative feedback from experienced geo-cachers who are suggesting significantly different coordinates. If I follow my coordinates, with my GPS, it gets me to the right spot.

 

Main cache in question is this, if it's helpful: GC4TGV9

[+BlackRose67]

I used the same on my eTrex 20 (with WAAS and GLONASS enabled) and have never had any complaints about coordinates being off.

 

I just take a single sample for 3 to 5 minutes, making sure that the sample confidence stays at 100% before ending the sample.

[+Chief301]

I usually go visit the site and take readings at least 3 or 4 times if I can, on different days. Most experienced cache hiders recommend this. I have the Oregon 550 so I'm not sure exactly what the process is on the Etrex 30, but I'm sure it's similar. On subsequent visits, when you start up the Averaging function, you should get the option to add readings to a waypoint you already have.

 

Further, sometimes it will show you 100% confidence within a few seconds if you have a good satellite fix that day. Don't go by the confidence level, go by the time of the sample...even if it shows 100% confidence, let it sit for at least a full minute....2 or 3 minutes is even better....let it settle down and take a good long sample.

 

These two practices, multiple site visits and longer sample times, should improve your coordinates.

[+MinionBrigade]

Further, sometimes it will show you 100% confidence within a few seconds if you have a good satellite fix that day. Don't go by the confidence level, go by the time of the sample...even if it shows 100% confidence, let it sit for at least a full minute....2 or 3 minutes is even better....let it settle down and take a good long sample.

 

These two practices, multiple site visits and longer sample times, should improve your coordinates.

 

Interesting. In general the eTrex takes about 6 minutes to get to 100% confidence. Looks like multiple visits is the key.

[+BlackRose67]

Interesting. In general the eTrex takes about 6 minutes to get to 100% confidence. Looks like multiple visits is the key.

Interesting. On my 20 it takes just under 3 minutes to get to 100%, unless I am under a heavy tree canopy.

[+chillypenguin]

Becouse of issues like you have discribed I have given up using my etrex30 and now use and android app as it's far more accurate!

[+MinionBrigade]

Interesting. In general the eTrex takes about 6 minutes to get to 100% confidence. Looks like multiple visits is the key.

Interesting. On my 20 it takes just under 3 minutes to get to 100%, unless I am under a heavy tree canopy.

 

Come to think of it, I think I did have one instance where it reconciled in about 3 minutes, but the tree cover isn't that different on my caches. I'm hoping to get a fellow 30'er so we can compare notes, but I'm really surprised your 20 is faster. Not sure what to make of that, I guess the color screen is interfering with the GPS? That was about the only real difference I saw when comparing the two (and Chirp). I almost bought a 20.

[+MinionBrigade]

Becouse of issues like you have discribed I have given up using my etrex30 and now use and android app as it's far more accurate!

Seriously?

[+Gitchee-Gummee]

Becouse of issues like you have discribed I have given up using my etrex30 and now use and android app as it's far more accurate!

Seriously?

Notice, (s)he did not say the geocaching.com Android app, just an(d) Android app.

There are apps available that do a really decent job of obtaining accurate coordinates. Some are designed for that function, only.

 

Although the "far more accurate" portion of the statement may or could be arguable.

Mileage of each individual device varies, even within brands.

[+Chief301]

Further, sometimes it will show you 100% confidence within a few seconds if you have a good satellite fix that day. Don't go by the confidence level, go by the time of the sample...even if it shows 100% confidence, let it sit for at least a full minute....2 or 3 minutes is even better....let it settle down and take a good long sample.

 

These two practices, multiple site visits and longer sample times, should improve your coordinates.

 

Interesting. In general the eTrex takes about 6 minutes to get to 100% confidence. Looks like multiple visits is the key.

 

I've made it a habit to power up the GPS way before I get to the cache location....that way it has 5 or 10 minutes while I'm driving to get a good satellite lock and track for awhile before I'm ready to take my reading. Then it gets 100% accuracy fairly quickly. If I wait until I arrive at the site to power up the device, even if it's showing that the satellites are acquired, it seems to take a lot longer to show confidence. Maybe just my imagination but this seems to be the case.

[+GeoTrekker26]

 

Not sure what to make of that, I guess the color screen is interfering with the GPS? That was about the only real difference I saw when comparing the two (and Chirp). I almost bought a 20.

 

I think you are not correctly remembering your shopping comparisons. The e20 & e30 have identical color displays. The big differences are the electronic compass, barometric altitude measuring and unit to unit data transfer. I doubt many would consider Chirp a major difference. Indeed Garmin doesn't even mention it on their comparison chart.

[+JohnCNA]

I have the eTrex 30 and whenever I select the averaging function it prompts that it's best to wait at least 90 minutes between readings. I assume that is to have the satellites in a different position than when the first reading was taken. With one of my hides that had a few DNF's I went back a couple days later and took another averaged set and was only .001 different on my North coord and the same on my West coord. I have a high degree of confidence in the eTrex's accuracy if I take the time to let it settle. I have it set to use GLONASS and WAAS.

[+MinionBrigade]

 

Not sure what to make of that, I guess the color screen is interfering with the GPS? That was about the only real difference I saw when comparing the two (and Chirp). I almost bought a 20.

 

I think you are not correctly remembering your shopping comparisons. The e20 & e30 have identical color displays. The big differences are the electronic compass, barometric altitude measuring and unit to unit data transfer. I doubt many would consider Chirp a major difference. Indeed Garmin doesn't even mention it on their comparison chart.

 

You are absolutely correct. Now that I think about it, my shopping comparisons were done between the 10 and 20 at Academy. I discovered the 30 at REI a few days later and bought it on a whim. So when it comes to differences between the 20 and 30 I know not whereof I speak.

[tr_s]

20 feet accuracy would be superb. I wouldn't be looking for systematic/receiver errors and reinvestigate the coordinates unless people are starting to suggest that coordinates may be 100 feet or more off the cache.

Waypoint averaging won't correct much for the atmospheric errors by the way, unless you take several readings hours/days apart and put together a linear average of those. (A poster above now writes the eTrex 30 might suggest this upon averaging, I haven't seen it yet!)

[+MinionBrigade]

20 feet accuracy would be superb. I wouldn't be looking for systematic/receiver errors and reinvestigate the coordinates unless people are starting to suggest that coordinates may be 100 feet or more off the cache.

Waypoint averaging won't correct much for the atmospheric errors by the way, unless you take several readings hours/days apart and put together a linear average of those. (A poster above now writes the eTrex 30 might suggest this upon averaging, I haven't seen it yet!)

 

[spoiler Alert for anyone thinking about doing my cache]

Here is one response I got from a seasoned cacher regarding a stage:

"At stage three I got to the location and I had the coordinates at 30 17.743, 81 39.089"

 

My coordinates for that stage are: n30 17.743 w081 39.093

 

That looks like a significant deviation on the west coordinate. Can you tell just from the numbers the distance involved?

[jholly]

20 feet accuracy would be superb. I wouldn't be looking for systematic/receiver errors and reinvestigate the coordinates unless people are starting to suggest that coordinates may be 100 feet or more off the cache.

Waypoint averaging won't correct much for the atmospheric errors by the way, unless you take several readings hours/days apart and put together a linear average of those. (A poster above now writes the eTrex 30 might suggest this upon averaging, I haven't seen it yet!)

 

[spoiler Alert for anyone thinking about doing my cache]

Here is one response I got from a seasoned cacher regarding a stage:

"At stage three I got to the location and I had the coordinates at 30 17.743, 81 39.089"

 

My coordinates for that stage are: n30 17.743 w081 39.093

 

That looks like a significant deviation on the west coordinate. Can you tell just from the numbers the distance involved?

 

Yes, it is about 21 feet. Fizzycalc is your friend.

[insig]

According to http://www8.nau.edu/cvm/latlongdist.html the distance between 030 17.743'N 081 39.089'W and 030 17.743'N 081 39.093'W is 0.0040 statute miles.

 

0.0040 miles is 21.12 feet.

 

EDIT: jholly beat me to it.

Edited December 4, 2013 by insig

[+Mineral2]

Perhaps you aren't understanding what waypoint averaging is, and the statistical significance of the confidence bar.

 

When you take an average, there is a variance that describes the distribution of points sampled to estimate that average. Your confidence in the average (or rather your standard error in the estimate of that average) is the sqrt(variance/n) where n is the number of points sampled.

 

Waypoint averaging takes a sample every second or so, and as you add more points, the effect on that average becomes smaller and smaller (your error on the estimate of the mean becomes smaller). The GPS's confidence hits 100% when adding points no longer affects the estimate of the mean, though really this can happen around 75%.

 

So, now you have your waypoint that was averaged with hundreds of points. You want to test how accurate it is by walking away and navigating to it. You find that the GPS gets you within 10 feet or so of the actual point. Great! Remember that when you're navigating, your location is reported one sample at a time, so the GPS may be off. Of course, as you stand still on or near your waypoint, you'll notice your distance randomly wandering around and the GPS reporting that you are 10 feet a way, then 30, then 25, then 7, then 5, then 4, then 13..... and so on. This random movement is norman and expected.

 

Ok, so you come back a few days later and take another averaged sample and the coordinates are off by a bit. This isn't really a fair comparison because the position of the satellites have moved and so the estimate of your position has moved.

 

But, your estimate is likely to only move within 10 feet.

 

The level of accuracy we're demanding out of consumer GPS units is unreal and ridiculous. I'm happy that my GPS can tell me which intersection I'm standing at, let alone which corner I'm on. When you get within 30 feet of a geocache, it's time to put down the electronics and navigate with your eyes using landmarks.

[+chillypenguin]

Becouse of issues like you have discribed I have given up using my etrex30 and now use and android app as it's far more accurate!

Seriously?

Seriously

 

Since the Garmin software update to fix the `Sticky` issue, the waypoint averaging on my etrax30 has been next to useless.

 

We use one of the original Google Nexus 7 tablets, with GPS Averaging app. I have had fewer comments about accuracy on caches placed with the Nexus than with the etrex. It's not infallible, I ended up with co-ords 20m off for 1 cache. But it's certainly as good.

 

Don't tar all Android devices with the same brush, there is a lot of variability with the GPS chip-sets. We now look back at the Android we stared with and wonder how we ever found any caches!!

[+MinionBrigade]

Perhaps you aren't understanding what waypoint averaging is, and the statistical significance of the confidence bar.

 

...

 

 

This was helpful and a good assumption. From studying the forum and getting information from other cachers, I knew that simply marking a waypoint with my GPS was supposedly not the best way to go when hiding a cache. Waypoint Averaging was needed, so when I purchased a dedicated GPSr, that was a necessary feature I made sure was included. Perhaps my methodology is wrong. It doesn't help that the Garmin manual doesn't actually mention the use of the feature. Here's what I do each time I hide a cache. Walk to the desired location, select Waypoint Averaging and tell it to 'Go'. Then set it down on my desired hidey spot and walk away. Every few minutes I check on it to see how far along the confidence bar is. When it's at 100% i'll click the button again to stop the process and record the coordinates. Those are then the coordinates for the cache. I do not, currently, return to take further samples.

[+ecanderson]

I have the eTrex 30 and whenever I select the averaging function it prompts that it's best to wait at least 90 minutes between readings. I assume that is to have the satellites in a different position than when the first reading was taken.

That is correct. Taking good averages at different times of the day gives you different constellation configurations to work with. Once in a while the PDOP will absolutely stink due to an odd alignment, and taking readings at different times aids in throwing out any outliers.

[+JohnCNA]

Since the Garmin software update to fix the `Sticky` issue, the waypoint averaging on my etrax30 has been next to useless.<br /><br />We use one of the original Google Nexus 7 tablets, with <a href='https://play.google.com/store/apps/details?id=org.destil.gpsaveraging' class='bbc_url' title='External link' rel='nofollow'>GPS Averaging</a> app. I have had fewer comments about accuracy on caches placed with the Nexus than with the etrex. It's not infallible, I ended up with co-ords 20m off for 1 cache. But it's certainly as good.

 

Don't tar all Android devices with the same brush, there is a lot of variability with the GPS chip-sets. We now look back at the Android we stared with and wonder how we ever found any caches!!

 

What firmware do you have on your '30? Mine is at 3.40 and I have not had any issues with placing waypoints.

 

After getting a Samsung Galaxy SIII, I compared the two during several cache placements. I use CacheSense on the phone, which has averaging built in. I set the two side by side and ended up with the exact same coords for North, and was .001 different with West. Or perhaps the other way around. The eTrex grabs sat lock much faster in heavy tree cover but once it has lock, the SG3 is VERY accurate. My wife has the iPhone5 and uses Geosphere. I've been able to compare all three while caching and I think the newest phones are close enough in accuracy that the average cacher would never notice the difference. The biggest difference will be the skill of the user.

[Fangamon]

To average quickly just place on ground == 1 minute!

[+MinionBrigade]

Since the Garmin software update to fix the `Sticky` issue, the waypoint averaging on my etrax30 has been next to useless.<br /><br />We use one of the original Google Nexus 7 tablets, with <a href='https://play.google.com/store/apps/details?id=org.destil.gpsaveraging' class='bbc_url' title='External link' rel='nofollow'>GPS Averaging</a> app. I have had fewer comments about accuracy on caches placed with the Nexus than with the etrex. It's not infallible, I ended up with co-ords 20m off for 1 cache. But it's certainly as good.

 

Don't tar all Android devices with the same brush, there is a lot of variability with the GPS chip-sets. We now look back at the Android we stared with and wonder how we ever found any caches!!

 

What firmware do you have on your '30? Mine is at 3.40 and I have not had any issues with placing waypoints.

 

 

Looks like my firmware is 3.10. Perhaps time to update that! They must have recently released new versions because the GPS is only about 3 months old, and i updated it as soon as I got it.