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What is averaging?


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Let's say you have a perfect spot for a cache. You want the most accurate coordinates possible. You mark a waypoint in your GPS & name #1. You now walk away from that spot, come back to the exact spot and mark another waypoint in your GPS & name #2. When you get home you add the two North coordinates together from your #1 & #2 and divide that by 2 to get an average. You do the same for the West coordinates. That's what averaging a waypoint means. On the Garmin 60CSX there is a function that will do this for you so you don't have to keep coming back to the spot marking waypoints. The longer you let it run, the better the average.

 

Not sure about your second question.

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1.) Averaging. Let's say you stand at one spot and just used the coordinates given on the GPS. You move and come back and stand at the exact same spot as before. You will get similar but different coordinates. You move for a third, fouth time and so on and comeback to the exact same spot and you get similar but different coordinates. These coordinates are averaged and give you a more accurate coordinates. Some GPS will do this for you. The only thing you do is hold you GPS for a few minutes in one spot. The coordinates will change as your body moves. So you get different coordinates. You GPS takes these coordinates and averages it.

 

2.) What version is your Garmin eTrex Vista? The Garmin eTrex vista C, Cx, and HCx has the averaging feature. The Garmin eTrex Vista does not appear to have averaging feature.

Edited by ssgeo83
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The Garmin eTrex Vista does not appear to have averaging feature.

The way to average with a unit that does not have waypoint averaging built in is to set track log to "log by time" then start a log and let it run for however long you want, and set an approprite time internal as well. For instance log every 5 seconds for 5 minutes, or every minute for 60 minutes. Stop the log when you are done. When you get home, download the track log into a spreadsheet and average the lats in one column and average the longs in another. It's easier if you use decimal degrees rather than DMS. Works great.

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I much prefer the way the 76CS series (and I would assume the 60CS series) do it. Mark a waypoint, select average, and let the thing take readings. I usually adjust the position of the unit until it gives me the best accuracy reading I can get and then let it average for a hundred cycles and then mark that as my spot. Of course, once I've done that I walk away and check if the unit takes me back to the spot. I check it using both the normal compass and the electronic compass. It seems to give me pretty accurate spotting.

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I see several misconceptions here already. This is a pet peeve of mine.

 

Averaging on a GPS is done by selecting the "AVERAGE WAYPOINT" function on your gps. It uses a different algorithm to factor in additional satellites to perfect your fix. It then shows you a timer counting the number of seconds that your waypoint reading has averaged in those extra satellites. From the Joe Mehaffey and Jack Yeazel website it has been shown that the best length of time to average a waypoint is 5 minutes.

 

It is NOT, and I repeat NOT, taking a bunch of gps readings, adding them up, and dividing by the total number of readings. Since the satellites are orbiting the Earth every 11 hours and 58 minutes it is quite likely that you will be utilizing a different satellite in your fix when you take different readings over time. If your fix uses a different satellite in its simple calculation then you will get a different end result. If you get a satellite with poor health in the fix then you are simply averaging poor numbers into your mathematical average. In the end...you are everaging in unknowns and the end result is pot-luck.

 

If your GPS does not have the "Average Waypoint" feature then you can't average. Don't be fooled into mathematically averaging a bunch of waypoint readings.

Edited by victorymike
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victorymike, are you saying that there is no value in taking multiple readings and mathematically averaging them?

 

Your definition of averaging is no doubt true, but it seems to me that mathematically averaged readings are better than picking one of the readings you've seen and using that as the cache's coordinates.

 

Visitors to your cache will hopefully see the same coordinates that you saw. If the values you list as the coordinate are in the middle of the set, then the visitors should not be too far off.

 

But then again, if you took lots of readings and decided to use the coordinates that you read more often than any others, you might help the visitors even more. Maybe this is what the averaging as you described it does.

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My experience shows me that it is probably more accurate for others with different gps's if you take a bunch of coords and divide manually. I find that if you let the gps average, your coords don't change making them more accurate only on that gps. I can't find documentaion on this, but try it and you'll see what I mean. The numbers don't change at all.

 

Hi all,

 

I have a few questions. 1) What is averaging? 2) Can it be done a on Etrex Vista? 3) If not, can I buy software to make it do so?

 

Thanks,

 

Phil

Edited by Team Lucky
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