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EPE and WAAS..


lthaus
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Howdy..

I'm looking for opinions, and I know most people have them..

 

I currently have a GPS12 and while I like this unit I would like to get a new GPS with more Icons and map ability.

 

I purchased GPS from the local WM and sat in my drive way to do a little test. My garmin 12 settled down with epe of 12 or 13, but the new unit with Waas on and locked never got below 21.

 

I marked a point in the chair I was sitting in and my ft drifted as far as 45 feet away.. All while sitting there. I walked down the street and back and it was closer, but it said I was 17 ft away. I'm not happy with the performance of this "new" unit and will take it back.

 

Question is, With "any" gps unit, should the epe be accepted or with a grain of salt? My G12 was steady the whole time. What experance does anyone have with the Garmin Vista or the Magellan Platnum? Those are what I am looking at next. My Garmin 12 is almost 5 years old.. but if it is as steady as the epe said, I may just keep it.

 

Thanks for any input..

 

Lthaus

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I was out side..sitting in the drive way.. clear sky.. and waas locked. The other thing I did notice was the Lat/Lon from my gps 12 was sitting still.. while the "other" gps was moving around in the .thousandths, not much..but still not steady. Should I turn it on and leave it in view of the sky for a few hours? Perhaps it needs to "Tune" in.. or at least settle down. I am not sure if it needs to load or calcluate the tables over time. It was fresh out of the box.

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What is the other unit? I have a 12 and a Map76. Don't take the EPE as gospel. It is an estimate of how your unit is doing. It is not true accuracy. With Waas the accuracy may drift around more until it has time to lock on and download the almanac from the sats. There are times when WAAS may do worse for you than not using WAAS. With Waas on, it prioritizes certain sats over others, and this may not always give you the best geometry. In the open, with a good WAAS lock, WAAS can often (usually) get you down to a few feet. Here is the comparison (as I recall) of my readings while on a benchmark with WAAS on and off:

 

Waas on:

Accuracy reading 6'

distance to target 0'-3'

 

Waas off:

Accuracy reading 14-17'

distance to target 7'-10'

 

Those are not exact but close. I recall my actual position was consistantly 40% closer than my EPE. Your EPE mostly just says 'your target will be somewhere within this distance about 90% of the time.

 

Comparing my 12 to my Map 76, the 76 will hold a signal in tree cover longer, but my 12 will give a more consistant postion.

 

4497_300.jpg

 

"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington

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Goodness yes! You need to (first time!) let it download the almanac till you see 'D's' on all the signal bars. Be patient! It takes a while the first time.

 

4497_300.jpg

 

"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington

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EPE is a funny animal and in an absolute sense really means little and can be quite deceiving. Simply by looking at displays generally doesn't give the overall picture as many will only see what they want to see.

 

The following are 3 receivers of the same make from different era's ranging from 1994 to 2002 (pre and post SA software versions), all recorded data and over the same 24 hour time frame, all Standard Positioning Service and effectively all different.

 

GPS1 1994 95% accuracy 6.2m EPE Range 8.9m to 101.3m

 

GPS2 1998 95% accuracy 4.8m EPE Range 2.8m to 6.4m

 

GPS3 2002 95% accuracy 3.1m EPE range 3.3m to 6.5m

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

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Yeah help me out too. What is EPE???

 

Now that you know I am a newbie I can say that my E-Trex Vista whenever putting in new batteries I have found to lay it on an open surfacr clear to the sky for about 10 to 15 minutes and do a compass calibration.

 

murph

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quote:
Originally posted by EraSeek:

Estimated Position Error. How far of target you may or may not be 95% of the time, maybe.


 

95% Maybe? now I'd like to see that in writing, signed by any manufacturers chief trust me signerer, willing to guarantee it.

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

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