Whats Wrong With My Gps?

[Guest angelwolf]

Can anyone help me I bought a Magellan 315 GPS about a month ago I went geocaching and placed some caches. I took my brother Inlaw out with his GPS and he couldn't find them his coordinants were about 150-250 FT. off. And All the people that have looked for my caches have said the same even when I've gone looking for caches mine was that far off. So I returned It and got another one Same brand and model, well I'm having the same problem. Any suggestions. Thanks

[Guest Tek465m]

Be sure to check to see what Datum you're using. WGS-84 is the standard for geocaching. Using any other Datum could possibly give you the error you're talking about.

 

Good Luck.

[Guest angelwolf]

Thanks for your help for some reason It was set on nad83 I guess the one I returned must have been to. The coordinance were completly different.

[Guest Kerry]

quote:

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Originally posted by angelwolf:

Thanks for your help for some reason It was set on nad83 I guess the one I returned must have been to. The coordinance were completly different.

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NAD83 is basically the same as GRS80, which for all intent and purposes is the same as WGS84. That wasn't the problem.

 

Cheers, Kerry.

[Guest BigDoggie]

Many things can affect GPS readings. Among them, tree cover, buildings, hills and valleys, and even cloudy skies or storm clouds!

 

When you get to your cache placing point, switch to your satellite display screen and make sure you have several satellites showing strong signals... at least 3 or 4, 6 or more is better. If not, move around a bit until you do, or hold the GPS up.

 

Be sure to WAIT a few minutes for the readings to settle, especially with a Magellan (so it can do position averaging.)

 

If your GPS doesn't do position averaging, then YOU should do so. Take your first set of readings. Walk 100' or more away from the cache, wait a couple of minutes, then walk back. Do the same thing a couple of more times, going in different directions each time. Then numerically average the minutes readings.

 

If you get wildly differect readings as you approach the cache site from different directions and at the cache site, so will your seekers! Try to solve the problem so each of you seekers won't have to!

 

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Interested in Geocaching in the state of Georgia? Visit the Georgia Geocachers Association home page at http://www.ggaonline.org

[Guest DaveA]

Not sure why you are getting such an innaccurate result. I use the 315 as well and find that it *usually* gets me to within 10 feet or so of a cache location assuming clear skies. The only time I was ever off by as much as you report was under 90% tree cover while on top of 600 feet of rock that went on for miles and even then I was only off by < 200 feet. And I suspect that at least half the error was the cache hider's coordinates as nobody's gps could avoid all the multipath present in this situation.

 

As was stated, make sure you are using the WGS84 datum and you should be fine. The only other thing I can think of, and it is a longshot, is that the automatic waypoint averaging feature on the 315 kicks in too early and this can throw you off. What I mean is that when your unit is in averaging mode it no longer displays the coordinates you are receiving, but rather it is displaying the average of all coordinates received while the unit has been in averaging mode. The 315 will enter and remain in averaging mode if you are moving at around 2 mph or slower. This is the only negative I have with the 315(later Magellan units have corrected this). You can know whether you are in averaging mode or not by looking at the first nav screen and it will say averaging or EPE.

 

It is possible that you slow down as you are investigating a potential cache spot, your unit starts averaging and as a result your position will be very innacurate as you move around, unless you move fast enough to get the unit out of averaging mode. I have learned that when I want to get a position with my 315, to stop, then walk quickly to my spot and stop again. This "forces" the unit out of averaging mode.