Averaging Coordinates
A Utility To Help You Establish Good Coordinates When Placing A Geocache
For Windows 2000, XP, Vista & Windows 7

 

07/25/2010
Click Here to Download The Program

Inaccurate coordinates can be a real pain when searching for a cache, so when I place my caches I want to have the coordinates as accurate as practical.  In an attempt to do this I take several readings in a session, waiting as long between readings as  practical.  After giving the unit about five minutes (more is probably better) to settle, I move it around a little so it will start a new average.  Then I let it average for about two and a half minutes without moving it.  I watch the last digits for the final 30 seconds to see if they're changing.  If they're changing I wait another 30 seconds -- still changing another 30.  I don't average for more than 3.5 minutes.  I capture my first pair this way, then walk a hundred or so feet away, return, do the average again and capture another pair.  Then go off in a yet different direction and repeat. I try to take three sets this way, but even if I don't have time to do the full averaging between readings I take at least three with the walking away between readings.    

The next time I'm at the cache location I do it all again.  If possible I come at a different time on a different day.  The GPS satellites are always moving, and their different locations can give better or worse results.  A different time is more important than a different day, so three times a few hours apart on the same day is better than the same time on three different days. 

 

Sidebar

If your unit does not average while remaining stationary, you'll have to take more readings to get good results.  I've never used a unit that didn't average, but if I were using one this would be my procedure: 

I would take at least 9 reading on each of 3 visits to the cache location.  I would use the above procedure but instead of waiting 2-3 minutes for each reading, I would take a reading, and without moving take another after about 15 seconds, and repeat for a third.  Then I would do the walk away and return, and repeat the three readings.  I'd do this 3 times for the 9 readings total.

A topic on the geocaching.com forums made me realize I need to add another point to this that I'd forgot to mention in earlier versions of this article.  I make a mental note of the EPE values when taking these readings.  I should jot them down, but usually I just remember them.  If my EPE values are high, say 30 feet or greater, I come back at another time.  If possible I try to only take readings when the EPE is 20 feet or less, preferably 13 feet.  I didn't normally get an EPE less than 13 when placing a cache until I got the Garmin 60C.  In the few caches I have placed I've never had to use readings when EPE values were as great a 30 and rarely greater than 20. If I ever have to I will mention it in the cache description.  A decent EPE is important.  A single reading at EPE 10 is likely to be better than the average of 3-5 readings at EPE 50.  Here's my article on EPE.

Both my SproTrak Pro and Garmin 60C must be held vertical to get the best signal.  I got tired of holding it, so I made this hook.  It's surprising how many things it will hang on.  The large end of the hook probably looks familiar:

I needed a way to combine all my readings into a single set of coordinates.  That's what this program does.  It works with coordinates in the typical geocaching format of degrees minutes and decimal minutes, like this:

N 29 35.715 W 95 05.051

I have revised the program from the original so you can enter (paste) coordinates in this format.  This way you can import them from your GPSr using a program such as GSAK and paste them directly into the program.  The original entry method is still supported and can be found near the end of this page.  Data files saved using the original format still work and will import correctly into this version.

New method

When you click "Plot" you get this display.

The blue + marks are plots of the individual readings.  The red + is the average of the individual readings.  I this case I would removed the outlying point on the far left.  An outlier is a point that is far enough away from the cluster of other points it doesn't seem like it's really part of the group.  You can delete points by right clicking on them.  After removing the outlier from the above set you get a revised plot and average.

If you don't think the average is a good center for the plotted points you can click at the location you think is the best center of the cluster and a green + will be put at the location of your choice and the coordinates for that location displayed .

Click on the prompt at the top of the screen to copy the final coordinates to your clipboard for pasting into another application.

Original Method

Normally I would only enter the decimal part of the minutes.  In this example I would enter 715 and 051.  In the very unusual case that you're near the minute change point, and some values have different minutes you will have to enter 4 digits.  For example, if one minutes value were 35.999 and another 36.000 I would enter 5999 and 6000.  You can enter the entire number if you want, but do not include the decimal and you must include 3 numbers after the decimal even if they're zeros -- e.g., 35999 and 36000.

When you click Plot you get a display like this
(Note:  Values are different because the screen shots were made at different times)

The blue + marks are plots of the individual readings.  The red + is the average of the individual readings.  I this case I removed the outlying point on the far right.  An outlier is a point that is far enough away from the cluster of other points it doesn't seem like it's really part of the group.  You can delete points by right clicking on them.  After removing the outlier from the above set you get the following revised plot and average.

If you don't think the average is a good center for the plotted points you can click at the location you think is the best center of the cluster and a green + will be put at the location of your choice and the coordinates for that location displayed .
 
Note:  Because the coordinates are so close together simple arithmetic is used.  Therefore this program will not give good results if trying to locate the center of coordinates that are miles apart.

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