no waypoint averaging

[dboggny]

my garmin etrex (base model) does not have waypoint averaging. i am concerened that if i were to hide a cache that when i took coordinate readings they may be too unreliable and people will not find the cache. does anyone have any advice on this to offer? can i walk away and back to the cache several time to get several readings and average them myself with simple math? thanks

[+DutchBoy]

I also have the basic yellow etrex. I usually do just as you said. I mark the waypoint, then walk away, come back, and mark it again. I do this about 5 times. Then I average the readings. Sometimes I even choose one of the waypoints, hit go to, then see how far it says it is off. Then I choose the best one. Hope this helps.

[+BrownMule & Jackrabbit]

quote:

---

Originally posted by dboggny:

my garmin etrex (base model) does not have waypoint averaging. i am concerned that if i were to hide a cache that when i took coordinate readings they may be too unreliable and people will not find the cache. does anyone have any advice on this to offer? can i walk away and back to the cache several time to get several readings and average them myself with simple math? thanks

---

 

None of the Garmin Etrex models average and in my opinion averaging is way over rated. Do as you said, take a couple readings and average them if it makes you feel better. I don't even bother to do that. I just make sure I have a clear view to the sky and a good lock and then I sit my GPS down for 5 or 10 minutes while I take a break and then record the waypoint. I do walk away and perform a goto to see how close I am before I leave the general area. No one has ever had any problems finding mine. I use an Etrex legend and Garmin GPS V.

 

[+BrownMule & Jackrabbit]

quote:

---

Originally posted by dboggny:

my garmin etrex (base model) does not have waypoint averaging. i am concerned that if i were to hide a cache that when i took coordinate readings they may be too unreliable and people will not find the cache. does anyone have any advice on this to offer? can i walk away and back to the cache several time to get several readings and average them myself with simple math? thanks

---

 

None of the Garmin Etrex models average and in my opinion averaging is way over rated. Do as you said, take a couple readings and average them if it makes you feel better. I don't even bother to do that. I just make sure I have a clear view to the sky and a good lock and then I sit my GPS down for 5 or 10 minutes while I take a break and then record the waypoint. I do walk away and perform a goto to see how close I am before I leave the general area. No one has ever had any problems finding mine. I use an Etrex legend and Garmin GPS V.

 

[Kerry.]

Averaging , do you really need it , No.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

Averaging , do you really need it , No.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Renegade Knight]

Averaging is of vital importance. No self respecting geocacher should ever set a cache without it.

 

Now that I have your attention, It's not overrated but you don't need it to set a cache. With a good reading you will be close enough. Plus averaging many points with a bad location won't make much difference. For averaging to really work you need to average for enough time for the errors to even out. Different constelations help. In other words, most people who do average don't get much better of a reading than you would with a clear sky.

 

When I've checked my average's I've been able to come back to within 4' of where I set my GPS. Maybe averaging makes it too easy?

[jfitzpat]

With due respect to annecdotal evidence, Kerry is right. In controlled tests, averaging actually yields less accurate results now that SA is off.

 

-jjf

[+BigNick]

I too use an etrex basic, and just last weekend someone could not find one of my caches. I revisited with my GPS and a WinCE palmtop and recorded almost 400 points over 15min, after averaging it agreed with the posted co-ords within .001 of a minute. Like Brownmule I too also leave the GPS sitting at the cache location while I sort the cache out, and take a measurement when I am done.

Cheers

Nick.

[+The Cheeseheads]

Personally, for the two I have hidden, I didn't do any averaging at all.

 

Both hides were done in two trips. The first was me going out and just looking for a good spot with the cache left behind in the car. Once I found a good spot, a took a waypoint and headed back for the car to get the cache.

 

I then set my GPSr (A Garmin Legend, BTW) to take me back to my hiding spot. Both times, it took me within 20 feet of the spot, which is probably as good as I can expect.

 

Besides, if the location were too exact, where would the challenge be?

 

[+gnbrotz]

I too keep the GPS (basic yellow) at the cache location while setting it. I take a minimum of 11 waypoints, throw out the high and low and average the rest. So far, I've gotten positive responses from searchers in regards to the coordinates.

 

Greg

N 39° 54.705'

W 77° 33.137'

[+Prime Suspect]

A few things you can do to get better readings:

 

1. Turn WAAS on. If you've got a good view of the sky (and the WAAS satellites) you can significantly improve your accuracy.

 

2. Turn WAAS off. If you're only getting WAAS data for a few of the satellites you have a lock on, you're better off deactivating WAAS. Otherwise, the unit will only use the few satellites with WAAS data to calculate a position.

 

3. Orient the antenna properly. A unit with a patch antenna (like the eTrex line) should be held horizontally. Other types of antennas should be held vertically (or if the antenna if movable, rotate it to the most vertical position).

 

4. Don't think you have to be standing next to the cache site to take a reading. If you have the choice of being right next to your cache location, but under heavy tree cover, or walking 15 feet away and having open sky, then head for the open sky. Chances are good that you'll get a reading that's more useful to a cache hunter that way. If you're good at math, you could adjust the readings accordingly (N/S adjustments are a snap, E/W is tricker).

 

5. Wait. Let the GPSr sit in one location for several minutes. Watch the lat/lon numbers, and wait for them to settle down. Try to not block signal reception with your body.

 

[+sbukosky]

I agree with the responses that say to set the Etrex down and let it be for several minutes. I have an eMap that averages if desired but I've noticed that if I let it have an undisturbed view of the sky, the accuracy will improve the longer it sits. So, don't worry that you don't have averaging. Just let it set for a while and that should be good enough. Remember, we expect that ground zero readings can be off by a 60 foot radius or so.

 

Steve Bukosky

 

Steve Bukosky N9BGH

Waukesha Wisconsin

[BassoonPilot]

quote:

---

Originally posted by Prime Suspect:

 

1. Turn WAAS on. If you've got a good view of the sky (and the WAAS satellites) you can significantly improve your accuracy.

...

---

 

I'm still waiting to see one authenticated example where WAAS provided more accurate readings than the same (consumer hand-held) unit with WAAS disabled. I've compared the readings on at least 200 cache searches, and have yet to see any gain in accuracy ... usually, it's been the other way around.

[peter]

quote:

---

Originally posted by BassoonPilot:

I'm still waiting to see __one__ authenticated example where WAAS provided more accurate readings than the same (consumer hand-held) unit with WAAS disabled. I've compared the readings on at least 200 cache searches, and have yet to see any gain in accuracy ... usually, it's been the other way around.

---

 

David Wilson's results at:

http://users.erols.com/dlwilson/gpswaas.htm

are the best documented that I've seen, but others have also reported that WAAS leads to greater accuracy when comparing the results to a *known location*.

 

Almost all the reports I've seen that appear to show a disadvantage when WAAS is enabled have been looking at the receiver's own reported EPE values. These values have never been properly defined by either Garmin or Magellan and cannot be taken as an indication of the actual accuracy provided by the GPS receiver.

[BassoonPilot]

quote:

---

Originally posted by peter:

... but others have also reported that WAAS leads to greater accuracy when comparing the results to a *known location*.

 

Almost all the reports I've seen that appear to show a disadvantage when WAAS is enabled have been looking at the receiver's own reported EPE values. These values have never been properly defined by either Garmin or Magellan and cannot be taken as an indication of the actual accuracy provided by the GPS receiver.

---

 

Been there, done that at known locations, and using my Garmin Vista, I have noted no improvement in accuracy or a decrease in accuracy using WAAS on every occassion.

[Kerry.]

This is taking things to the extreme as WAAS doesn't give "proper" coverage over this way but we certainly receive the signal (POR) but just happen to be way way outside the ground station network which is where WAAS gains its accuracy capability.

 

everybody keeps telling me where to go

[Kerry.]

This is taking things to the extreme as WAAS doesn't give "proper" coverage over this way but we certainly receive the signal (POR) but just happen to be way way outside the ground station network which is where WAAS gains its accuracy capability.

 

everybody keeps telling me where to go

[Guest mcb]

Averaging does make a difference but I don't think most geocachers have the patence to wait long enough. Averaging for 5 minutes is not going to help a bit. Maybe 15-30 minute and you'll make some improvement. Averaging for a few hours really helps and for 12 or more hours it will make a big difference. I make shift average would be to mark a cache and them come back a few hours later and mark it again, and repeat a few more times. Average these point. The fact that you have left and come back makes not difference what you are looking for is different satellite geometry.

 

As for WAAS I have seen a big difference in my own navigation. As for seeking a cache remember your dealing with the error from your own unit and the error introduce by the hider's unit. Also keep in mind the the further you are from a ground correction station the less benificial WAAS will be.

 

Another tip when marking or averaging a cache's position is to move GPS so that it has the most possible number of satellite lock on as possible. This will help you accuracy more than most other things.

 

mcb

 

GPS-Yote

[+Alan2]

In checking my Vista against a NGS benchmark, I was 1 meter to 4 meters from the actual with four diferent readings. The one meter was off on a Wass reading and also without WASS. The sky was clear, no obstructions and the GPS sat on the benchmark from a few second to a few minutes only.

 

Others did the same "test" and posted their results on my web page. With many different GPS models being used by different cachers, the results were amazingly close to the actual coordinates.

 

If someone could analyze the results in some form of table, it would interesting to see what the overall results are.

 

Here's the cache page.

http://www.geocaching.com/seek/cache_details.asp?ID=10814

 

Alan

[Kerry.]

One can analyse endless amounts of data but averaging is certainly never going to be as important as being at a certain place at the best time.

 

There will generally be that unknown and with some planning the "best possible result" can be achieved but that doesn't always suit as one can not always be at a certain place at the "best" possible time.

 

These are actual examples but in no way are what might be expected elsewhere, it could even be worse but then things might be better, that's one of the problems, the unknown can be about 50/50.

 

The results of averaging and the followup Affects of averaging part II as well as the Affects of averaging with obstructions

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

One can analyse endless amounts of data but averaging is certainly never going to be as important as being at a certain place at the best time.

 

There will generally be that unknown and with some planning the "best possible result" can be achieved but that doesn't always suit as one can not always be at a certain place at the "best" possible time.

 

These are actual examples but in no way are what might be expected elsewhere, it could even be worse but then things might be better, that's one of the problems, the unknown can be about 50/50.

 

The results of averaging and the followup Affects of averaging part II as well as the Affects of averaging with obstructions

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[abombone]

If you want to average with any of the etrex series, you can download your tracklog. My favrite software for that is Waypoint:

 

http://www.tapr.org/~kh2z/Waypoint/

 

export your tracklog as a comma delimited text file and you can use excel or whatever to average, throw out outliers, you name it.

 

WAAS is tricky; if you are in the wrong place, haven't received the full almanac and ephemeris, etc. it will definitely throw you off. WAAS only became a reality in Georgia a few months ago, and I'm seeing better results with it than before. Expect to take longer with it in any case. More info is at

 

http://edu-observatory.org/gps/dgps.html

 

(follow the links at the bottom of the page).

 

Whatever you do it will help to visit your cache at different times of day as the different satellite geometries will affect your results. The geometries approximately repeat every 12 hours, so 2-3 hours should make a difference (the exception is the WAAS satellite, which is always in the same place: toward the southeast over the eastern US; southwest in the western).

 

Good luck!

[+Alan2]

quote:

---

Originally posted by abombone:

If you want to average with any of the etrex series, you can download your tracklog. ...

 

Whatever you do it will help to visit your cache at different times of day as the different satellite geometries will affect your results. The geometries approximately repeat every 12 hours, so 2-3 hours should make a difference (the exception is the WAAS satellite, which is always in the same place: toward the southeast over the eastern US; southwest in the western).

 

Good luck!

---

 

The cache visitors to my NGS benchmark cache http://www.geocaching.com/seek/cache_details.asp?ID=10814&logs=y&decrypt= visited over a four month period at different times during the day. Some averaged, some didn't, some did both. Diffrerent models were used by cachers of different experience. This is a real world situation.

 

WOuld you like to analyze and post the results here in a table or spreadsheet. I thin it would be interesting to see the results.

 

Ttks

Alan

[+Alan2]

The analysis can be found in topic: "GPS Accuracy in a real-world geocache test" in the GPS Units and Software section.

 

ALan