# "Averaging" coordinates

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I have seen people publish on their cache pages that when they placed the cache, they averaged the coordinates , and sometimes, they even say how many times they averaged them.

What is the purpose of this, and how many different sets of coordinates would you use to come up with your average? I've seen some people say they averaged as few as 5 and as many as 200.

I don't average. I set my GPSr down and let it crank out a solution while I do other stuff.

I don't average. I set my GPSr down and let it crank out a solution while I do other stuff.

That's pretty much been our approach, too.

I have seen people publish on their cache pages that when they placed the cache, they averaged the coordinates , and sometimes, they even say how many times they averaged them.

What is the purpose of this, and how many different sets of coordinates would you use to come up with your average? I've seen some people say they averaged as few as 5 and as many as 200.

Well, as you know, the accuracy of the coordinates your GPS is giving you will vary from minute to minute and day to day due to all kinds of variables. So what many people do is take several coordinate readings over the span of a few minutes, at the very least, up to a few days (i.e. they make multiple trips). Then they take an average of those numbers.

Suppose I place a cache. I put my GPS down on the rock where my cache is hidden, and let it sit for a few minutes. It seems to stabilize on minutes coordinates of 15.101 and 25.850 (degrees portion omitted for simplicity). I go for a bit of a walk and come back and do it again. This time I get 15.109 25.843. I go back the following day and I get 15.106 25.851. That's three sets of coordinates. I'll average them, to get a final set of coordinates 15.105 25.848, which is what I post on the website.

All I did was average (101, 109, 105) and (850, 843, 851).

Some GPS units have a built-in averaging function where you just leave it in the spot for a while and let it crunch the numbers for you.

My GPS does it for me. The 60CX sereies have an auto averaging thingy. It takes readings every second or so, and averages them against one another. I think it does a fair job....seems to work for me.

My GPS does it for me. The 60CX sereies have an auto averaging thingy.

I use the same function on my GPSMap76S. After one or two minutes the averaged coordinates are very accurate.

My GPS does it for me. The 60CX sereies have an auto averaging thingy. It takes readings every second or so, and averages them against one another. I think it does a fair job....seems to work for me.

The Garmin V also has that function, and I suspect many other Garmins do, as well. I'm guessing their competitors' models may also have that capability.

The Garmins will easily average your location several hundred times in the time it takes to sign the logbook and trade swag. I do this when the my coords differ significantly from the cache's posted coords after accounting for the accuracy reading (EPE) at the time. I then post those coords in my online log in case anyone wants to try them.

Edited by worldtraveler

I'm guessing their competitors' models may also have that capability.

Some Magellan GPSr automatically start averaging if the receiver is not moved for some seconds.

I take individual readings and I also let my 60CS auto-average several times. I do both over several days. Quite frankly, no matter which way I do it, I come out very much the same. The bigger variances, in my particular experience, have occurred from day to day readings. All my readings on a particular day have been very close to each other.

A lot of the newer models have an average function built into them. I have a 76CSx (the 76CS I had previously had this also) and I can push the Enter button to create a new waypoint and then cursor over to the AVG button and let it cycle through readings. It doesn't take long to go through 100 or so sample readings and it gets the coordinates pretty darn close to actual ground zero.

I have a friend with a Legend and it doesn't auto average. He approaches his caches from numerous directions, angles, etc. under different conditions and gets the coordinates amazingly accurate. Of course he hides micro caches with insane camo so the only way you can find some of them is the fact that you can count on his coordinates being right on the money.

I have seen people publish on their cache pages that when they placed the cache, they averaged the coordinates , and sometimes, they even say how many times they averaged them.

What is the purpose of this, and how many different sets of coordinates would you use to come up with your average? I've seen some people say they averaged as few as 5 and as many as 200.

When I first started placing caches I did average. I would take about 20 readings by standing at the cache, marking, walking away, returning and marking. Then I would throw away the farthest off and average the rest.

Eventually I realized that any benefit was so minimal that it was a waste of time, so I stopped averaging and my coordinates are no better or worse now than then were when I averaged.

My GPS does it for me. The 60CX sereies have an auto averaging thingy. It takes readings every second or so, and averages them against one another. I think it does a fair job....seems to work for me.

Yep, when my 60CSx came I was sitting in my recliner looking it over and found the averaging feature, I let it average my location and locked in the waypoint. Next evening I sat in the same recliner and checked, it said I was 3 feet off. Not bad at all, although I haven't checked it again since.

I agree with Briansnat though, as long as you get a good signal and let it stabilze you shouldn't need to average it, the hunters won't average theirs, they'll just get close and start looking.

In the old days.... way back in 2002, we used to have very inaccurate gps receivers.

They would only grab 3 satellites, and wandered all over the place.

Back then, we would take 3 or 4 readings, and average them out.

You can get 12 satellites, and the receivers can take a reading every second or so, and average them out for you.

However, if you want to see how different satellites 'drift', then set your gps on a table in the yard, and zero it out. Then let it sit there for a couple of hours and check the trackmap. It will have moved around the yard...sometimes up to 30 or 40 feet.

I don't average. I set my GPSr down and let it crank out a solution while I do other stuff.

That's pretty much been our approach, too.

That is want I do to.

Averaging will produce more accurate coords than a single reading. Averaging several times at intervals of 30 minutes or more should give the best results. If satellite geometry or signal reflections are causing a substantial error, averaging for say 10 minutes will not reduce the error by much, and the averaged coords may be off by 50 feet or more if signal reflections are present. If you come back to the location later, satellite geometry may change enough to eliminate the reflection problem and allow accurate readings. I see a lot of posted coords that are off 50 feet or more due to signal reflections, almost always on or near a rocky slope.

Edited by CharlieP

If you have a GPS where you can turn the averaging function on and off, and have the time to do it, then go ahead and take a few hundred readings. If you have to do it manually, I wouldn't bother. The fewer readings you take, the greater the chance that a single bum reading will really throw off the results.

I make a waypoint, leave, come back and make another waypoint,

repeat a few times.

then I just look at the map, and make the final waypoint in the spot that looks most likely to be the correct one, in the middle somewhere.

This is what I do to find the waypoint for my cache. It takes a while.

I hide the cache, place the GPS on the cache and take a location reading, then I walk away and download the coordinates. I turn the GPS off and on and then walk to ground zero. When I get to ground zero I pull out my compass and see how far away from the cache I am. Depending on where I am to the cache I'll add degrees/minutes to the North coords if I need to go north and subtract from the North coords if I need to go south. I'll add degrees/minutes to the West coords if I need to go west and subtract if I need to go east to get to the cache. So for example if I am southwest of the cache then I'll add a few degrees/minutes to the North coords and decrease a few degrees/minutes from the West coords. Then I'll walk away again and follow the new coords for ground zero. This way I slowly zero in on the right coords that will take me to the cache each time( or as close as I can get).

My real trouble comes from low batteries. Ended up in the next county one time because of bad batteries. .

Edited by Luckless

What? Now I'm really confused.... Stop walking around, you're making me dizzy...

Just mark the waypoint. If the coords are not very good, every cacher that finds it will correct you.

Getting good coords when placing a cache can be tricky at times. Heres my favorite method.

As I approach the location I'm hiding the cache, I first roll down the window and decrease my speed to under 15 MPH. With my gps is one hand and the film can in another, I toss the film can out the window and mark the location at precisley the same time.

I've had a few complaints that my coords are off, but I think they are garmin users so I usually just disregard them.

Another way I do it is to just set my gps down and let it average itself as I cover the ammocan with rocks, sticks and whatnot.

I rarely get complaints on those caches as they are usually being found by Magellan users.

An alternative to averaging is to guess the position of the cache in relations to some object around it about the size of a car and then adjust what the GPSr gives you with satellite images that you can get in Google. This does not work if the cache is hidden in a bunch of trees or is somewhere that no good sat images exist.

I rarely get complaints on those caches as they are usually being found by Magellan users.

Never mind. Way too easy.

Edited by Prime Suspect

"every cacher that finds it will correct you. "

Hehe, don't I know it.

I use the auto-averaging if the accuracy is showing low numbers that day. I also make at least a few waypoints to check against the average that comes up.

If the accuracy is off by too much, I usually make at least 8 waypoints using the "walk away 30 feet and return method" throwing out any outliers, and averaging the rest.

A couple of qualifiers:

If one set of numbers appears over and over in the set, I just go with those.

I check them with the online maps to make sure they seem to direct folks to the spot.

I get many compliments about my coords being spot on.

If your unit has auto-averaging then use it, otherwise don't bother.

You have to average a minimum of 30 or so to get any real improvement in accuracy, and that becomes a hassle.

If you come back on another day to get a 2nd set of reading, choose a different time of day. The satellites are nearly in the same position at the same time each day, varying by about 4 minutes or so.

they averaged the coordinates

Every time I see this I know the coordinates are going to be off. some cachers think they can do a better job of averaging coordinates then the GPS in there hand that has a bulit in computer that averages the coordinates.

Just make sure your GPS has been turned in for at least 15 minutes and you will get a very good reading.

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