EPE

[XMIT]

Hi All,

 

Still learning gps and how it works. I am currently using an Ifinder. I bought this unit for boating and work. Then I discovered Geocaching. Fun Fun. Now I am wondering how my Ifinder compares to other units accuracy. My EPE on a clear day in Texas (after noon), with no foilage attenuation, is at best 34' EPE. In foilage (w/o leaves now) it is around 100'+. I was just curious what other units EPE is under simular conditions. I wonder if EPE is really the bottom line on how accurate my GPS is, being that it is an estimated figure. List your EPE if you wish.

 

Thanks and happy holidays,

 

XMIT

[+robert]

My Magellan SporTrak Color will get down to 7 on REALLY good days, and 13-16' on others. If the day is really crappy, 20' is about the worst it will get.

[+TotemLake]

I will typically see from 10-20' EPE. I have had it down as low as 7 on a few days and once even saw the EPE at 0'. I was absolutely astounded and had to show it to somebody else so I could have a witness. I was on the highest hill on an island with good horizon to see the WAAS.

Edited December 17, 2003 by TotemLake

[+EraSeek]

Now I am wondering how my Ifinder compares to other units accuracy. . I wonder if EPE is really the bottom line on how accurate my GPS is, being that it is an estimated figure. List your EPE if you wish.

Not to worry. The EPE is an estimate only of how your unit is doing. It is NOT truely an accuracy reading. Your Ifinder is probably simular to other units in accuracy. The best way to see how good it is, is to find a survey marker which is rated for horizontal measurments and stand on top of it with your gps set to GOTO its coordinates. This will show you how well the gps does, as well as how inaccurate you EPE reading is as an accruacy gauge. Really what the EPE is saying is "the target will be within 30' 95 percent of the time". Of course it may 2' away or 29' away. It may even be 50' away given the other 5 percent of the time. It is only an estimate gauge, based on what kind of satelitte fix you have, and the programing that produces the EPE reading.

[+GeckoGeek]

Now I am wondering how my Ifinder compares to other units accuracy.

How long did you let it run? Even after the GPS unit has a fix it will still acquiring more satellites and downloading the data to be able to make the most use of them. If you haven't used your unit in a few days it can take a good 10 - 15 minutes before it really locks in with a good EPE.

 

If you haven't already, invest in a set of rechargeable batteries so you don't care about burning electrons so you'll keep the unit on more.

 

Also, keep in mind that simply having a good overhead view isn't enough. A good view toward the horizon will help it pick up more sats at more angles. Having 3 sats that are almost overhead isn't going to give you a very good fix. But if you can have 3 sats that are out near the horizon, then it can compute the distance much easier.

 

With that thought in mind, make sure you're holding the unit right. Some like to be held flat with the display facing the sky, others like to be held upright with the display facing the horizon.

 

Everything else said and done there is variability in the sats themselves. Sometimes they aren't in a good position or the few that are in site are behind obstacles. So you can get two different results on two different days with nothing being noticeably different.

[Day Late AV8er]

XMIT,

You might want to try a program called "SA Watch". With this program you can connect your GPS to your PC and "Watch" the accuracy/drift of your unit right on your monitor.

Go to www.huntting.com/sawatch/ for more info. Its a shareware program and free download. Its a cool program.

[Kerry.]

Trying to compare EPE's between different makes/models is really a lost cause, means very little if anything at all.

 

For a particular unit the relative movement is probably a more meanifull indication of the position improving or getting worse, but in absolute terms don't mean all that much

 

Cheers, Kerry.

[+Prime Suspect]

Now I am wondering how my Ifinder compares to other units accuracy.

That's comparing apples to oranges. Each manufacturer has their own algorithm for calculating this. There's no industry standard.

[+apersson850]

Since the different manufacturers want their figures to look good, chances are that the EPE has a 50% probability, rather than 95%.

[Kerry.]

Since the different manufacturers want their figures to look good, chances are that the EPE has a 50% probability, rather than 95%.

Funny that manufacturers never really liked the 95% figure eventhough it's what system accuracy is generally based on.

 

CEP (that 50% figure) was obviously one of those little invented specifications to confuse accuracy.

 

Cheers, Kerry.

[+Cornix]

Here's a short overview article:

 

Error Measures: What does this all mean?

 

Your GPS's EPE readout is just a "figure of merit".  It is NOT an indication that the given position readout is within "EPE" feet of absolute perfection.

 

Cornix

[XMIT]

I think the best suggestion for me on this subject was by EraSeek. Going to find a know set of coords (BM) and camp on it till I am satisfied. All of your suggestions and replies were helpful.

 

Thank You,

 

XMIT