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Average waypoints with an iPhone (and EPE?)


teambaconpancakes
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We're planning on hiding our first cache this weekend, and after reading about how to average a waypoint I still have some questions.

 

We don't own or have any access to a GPS device other than our iPhones with the Geocaching app on them. Will this work for collecting waypoint coordinates? (I'm assuming I just get the coordinates of my position off that first main page of the app?)

 

Also, what does "EPE" mean? On the forum stickie about averaging waypoints, it talks about EPE and lists some example waypoints with EPE's included in feet. What are these, are they necessary, and how do I find out what my EPE is on my iPhone?

 

Thank you!

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EPE means Estimated Position Error. Its only value is for you to have a feeling for how good the reception is of the satellite signals. A smaller EPE means the GPS is getting better (more) information than when there is a larger EPE. It is of no value in absolute terms of knowing the accuracy of a given reading. Pay a lot of attention to the first word, "Estimated."

 

Also, newer iPhones are likely to be more accurate than older ones like the 3 or 3gs. I understand there are apps for the iPhone that will help you average coordinates.

 

Once you have your coordinates, you should go back the following day and navigate to the coordinates to see how close it gets you. If the terrain allows, do this from several directions.

 

Good luck with your first hide. Be sure you have read, reread, and then read again, the guidelines. Pay particular attention to the proximity rules. It looks like most of the places along the river have been taken and what appear to be available spaces are likely taken by puzzle or multi caches.

 

Have fun!

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We don't own or have any access to a GPS device other than our iPhones with the Geocaching app on them. Will this work for collecting waypoint coordinates?
Well, before the iPhone 4, the GPS system in iPhones earned a reputation for being inaccurate. It was fine for figuring out which street you're driving down, but not really accurate enough for geocaching.

 

But if you don't trust your coordinates, then test them. Enter them into your device, and use it to approach your cache location from at least 100ft away. Repeat the process, approaching your cache location from various directions. No matter which direction you approach from, the arrow on your device should point at the cache location. If it doesn't, then you need to adjust the coordinates and repeat the test.

 

Bonus points for repeating the test on a different day, when the GPS satellites are in a different configuration.

 

Also, what does "EPE" mean? On the forum stickie about averaging waypoints, it talks about EPE and lists some example waypoints with EPE's included in feet.
EPE is the Estimated Position Error. It is a statistical estimate of how far from perfect the reported coordinates are likely to be. Actually, it kinda works the other way around. Given a specific threshold (say, 75%), the system estimates the distance for which the probability matches the threshold that the reported coordinates are within that distance of the true coordinates.

 

So if the threshold is 50% and the EPE is 5ft, then 50% of the readings will be within 5ft of the true coordinates, and 50% of the readings will be more than 5ft from the true coordinates.

 

And if the threshold is 95% and the EPE is 15ft, then 95% of the readings will be within 15ft of the true coordinates, and 5% of the readings will be more than 15ft from the true coordinates.

 

Or at least, that's the device's best guess, based on the signals it's receiving from various GPS satellites. But the important thing is that an EPE of 10ft does not mean that you're 10ft from the true coordinates. It means that the device thinks that you're probably within 10ft of the true coordinates, for some definition of "probably".

 

I can't help with specific details though, since I don't use an iPhone. Sorry.

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