Waypoint averaging

[+UNIBear]

Since my yellow Garmin etrex doesn't have waypoint averaging, I need to know the best way to put the coordinates down for a new cache. I mean, do you walk up to the cache site 10 times, write down the coordinates each time and then do an average? (Do those degrees, minutes, and seconds add up and divide just like a "regular average"???) I want my cache coordinates to be accurate, but I also want to get it done as easily as possible. Thanks! UNIBear

[+Markwell]

Click here.

 

Empirically, it has been shown that averaging within a short period of time (less than an hour) does not significantly increase accuracy.

 

Anectodtally, I can say that I feel like I've gotten better results with averaging. Besides, it's another excuse to stay out in the woods just a little longer.

 

Markwell

Chicago Geocachers

[+Markwell]

Click here.

 

Empirically, it has been shown that averaging within a short period of time (less than an hour) does not significantly increase accuracy.

 

Anectodtally, I can say that I feel like I've gotten better results with averaging. Besides, it's another excuse to stay out in the woods just a little longer.

 

Markwell

Chicago Geocachers

[Kerry.]

If it feels good then do it but if you achieve a result less than 13m 95% of the time (actually a little more since that's based on SIS) then you've achieved the system's specifications.

 

Actually maximizing the constellation by being on site at the best time of day would give a greater sense of "knowing" that you've taken full advantage of what the system could provide on that day, which would be more important than averaging as averaging bad coordinates only produces a bad average.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

If it feels good then do it but if you achieve a result less than 13m 95% of the time (actually a little more since that's based on SIS) then you've achieved the system's specifications.

 

Actually maximizing the constellation by being on site at the best time of day would give a greater sense of "knowing" that you've taken full advantage of what the system could provide on that day, which would be more important than averaging as averaging bad coordinates only produces a bad average.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+briansnat]

In the beginning I used averaging, the same way you sugggest. I'd mark a waypoint, walk away a few steps, return and mark another. I'd repeat this about 10 times, sometimes more.

 

Despite this, I'd ocassionally receive complaints about my coordinates (as I'm sure everyone does). The one cache I receive the most complaints about is the one I took the most averages of (20).

 

Now I just make sure I have good reception (to less than 25 feet or so), lay the GPS down near the cache, wait a few minutes and mark a single waypoint. I still receive the ocassional complaint, but no more than when I took 10 or more averages. In fact a few of my recent caches have had finders remarking about how accurate the coordinates were

 

"Life is a daring adventure, or it is nothing" - Helen Keller

[+leatherman]

I wouldn't call it averaging, to avoid cofusion with the averaging feature available in GPSr units.

I don't think any special math skills are necessary. With all the readings I took I simply pick the most frequent coordinates.

Yes I do walk back and forth, from the cache location. Every position your GPSr is in recieves slightly different "obstructed signals". Meaning every tree, leaf and branch effects the timing of the signals reaching you reciever. Flat surfaces,like buildings, reflect the sat signals. I work in a small octigon shaped shack like structure on the roof of a building, with large windows on all sides. When I work on my waypoints in there, the GPSr says I am moving back and forth in all directions. Hundreds of yards in all directions. Even barometric pressure effects your receiption. Last week I was in Eugene Oregon. Eugene is in a valley, with no real mountains within miles. Just a very flat plain. Well I went out on a cache, and as I was standing on a bridge 30' above a river. A hundred yards away from the nearest tree. I lost all my satilite locks. I stood there stairing at my GPSr for twenty minutes, turning it off and on. The signals would spike up and down. At one point it showed me in Cambodia. Well it settled down and I found the cache. However I didn't get good receiption untill I drove out of that plain towards Portland.

Well my point is, there was a static dome of humidity over the valley. It was very hot also.

This type of atmospheric condition is like a big reflective dome above you.

If you lay your GPSr down or stand in the same place for averaging. Your just recieving the same bad or obstructed signals and averaging them. If you move around you allow the GPSr to recieve different signals, as if your aproaching from different directions. People searching for the cache will not walk in your exact foot steps anyway.

The comments I recieve on my caches say that my coords are right on. The few bad comments I just shrug off as their GPSr or bad receiption day.

 

Dissclaimer:

This is only an opinion. This is a compillation of experiences with three specific GPSr units. These experiences may or maynot add or detract from the specific capabilities of other units of the same makes or models. Any experiances or opinions by this user may or maynot support or conflict with the experiances or opinions of other users, and will not be held in debate.

This is only an opinion.

 

Preperation, the first law to survival.

[+leatherman]

I wouldn't call it averaging, to avoid cofusion with the averaging feature available in GPSr units.

I don't think any special math skills are necessary. With all the readings I took I simply pick the most frequent coordinates.

Yes I do walk back and forth, from the cache location. Every position your GPSr is in recieves slightly different "obstructed signals". Meaning every tree, leaf and branch effects the timing of the signals reaching you reciever. Flat surfaces,like buildings, reflect the sat signals. I work in a small octigon shaped shack like structure on the roof of a building, with large windows on all sides. When I work on my waypoints in there, the GPSr says I am moving back and forth in all directions. Hundreds of yards in all directions. Even barometric pressure effects your receiption. Last week I was in Eugene Oregon. Eugene is in a valley, with no real mountains within miles. Just a very flat plain. Well I went out on a cache, and as I was standing on a bridge 30' above a river. A hundred yards away from the nearest tree. I lost all my satilite locks. I stood there stairing at my GPSr for twenty minutes, turning it off and on. The signals would spike up and down. At one point it showed me in Cambodia. Well it settled down and I found the cache. However I didn't get good receiption untill I drove out of that plain towards Portland.

Well my point is, there was a static dome of humidity over the valley. It was very hot also.

This type of atmospheric condition is like a big reflective dome above you.

If you lay your GPSr down or stand in the same place for averaging. Your just recieving the same bad or obstructed signals and averaging them. If you move around you allow the GPSr to recieve different signals, as if your aproaching from different directions. People searching for the cache will not walk in your exact foot steps anyway.

The comments I recieve on my caches say that my coords are right on. The few bad comments I just shrug off as their GPSr or bad receiption day.

 

Dissclaimer:

This is only an opinion. This is a compillation of experiences with three specific GPSr units. These experiences may or maynot add or detract from the specific capabilities of other units of the same makes or models. Any experiances or opinions by this user may or maynot support or conflict with the experiances or opinions of other users, and will not be held in debate.

This is only an opinion.

 

Preperation, the first law to survival.

[+MrGigabyte]

quote:

---

Originally posted by UNIBear:

do you walk up to the cache site 10 times, write down the coordinates each time and then do an average?

---

 

Unfortunately, you may think you improving you accuracy this way, but in reality, you are doing nothing (except maybe trapping a gross error). Ten minutes of readings means 20 waypoints recorded with no consideration to the geometry of the satellites. To be of any value, the geometry must change. The birds move 30 degrees an hour, so waiting even half an hour is a big improvement.

 

All you may be doing is getting an average of bad data. It may be accurate but it is not precise. They may all be within 5m of each other, but they may also all be 100m out!

 

How you get the average is irrelevant. Whether by rigorous (least squares) or semi-rigorous (guesstimate) methods does not make any difference, if the average you come up with is based on questionable readings.

 

Moving is very important if it means moving to a location where the view of the sky is improved over the exact spot you have hidden or looking for the cache. Simply moving to the other side of a tree or even 10m or more may improve your precision by several orders of magnitude. You can always manually adjust the latitude and longitude later knowing that 0.001 minutes is roughly 2m.

 

Get to know your satellite screen. It is the best information your GPSr provides.

 

Keep an eye on the satellite page. Wait until you have the best reception and geometry and then set a waypoint. If you have to move 5m to get out of the tree shadow, then do so. Moving that 5m may increase your accuracy by a factor of 10.

Now keep watching the satellite page for as long as you can stay there. Take more waypoints. Just wait, be patient, improve your view of the sky and take multiple waypoints ONLY when the satellite view is good. The longer, the better.

Now, just zoom right in on your map screen on your GPSr and manually select the best position (be it a recorded waypoint or not) from the grouping of waypoints you recorded.