MnGCA

Moe the Sleaze · Posted: Mon Jan 19, 2004 7:04 pm Post subject: GPS Accuracy

I've been noticing a lot of logs lately where the finder takes issue with the posted coordinates because their GPSr indicated they were off by 20 feet or less! What some people don't seem to realize is that because accuracy can be affected greatly by tree/leaf cover, nearby buildings/bluffs, or simply by the constellation of satellites, 20 to 25 feet of accuracy is often as good as one can hope for. Now, the hider may have 20 feet of accuracy when he hides the cache and the finder may have similar accuracy in the opposite direction which would result in a perceived error of 40 feet!

Personally, I rarely post "corrected" coordinates unless my reading is off by more than 0.01 minutes (approx. 60 feet) unless I have good reason to believe my coordinates are significantly better and the hide is in a "target rich" area (ie. the cache is a micro and there are a hundered spots to hide it in a fifty foot radius).
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"Hi, I'm Moe, or as the women know me - Hey! You in the bushes."
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RJ · Posted: Mon Jan 19, 2004 9:39 pm Post subject:

I rarely change the coords on caches I've posted unless I get many posts on the inaccuracy of my coords. 20 feet or less is pretty good if you ask me. I used to think that 30 feet was about average.

Marsha and Silent Bob · Past MnGCA President Joined: 02 Sep 2003 Posts: 6261

SirPoonga · Posted: Mon Jan 19, 2004 9:45 pm Post subject:

Yep, mathematically you could be a ways off.

Ok, lets say your gps is getting good coverage and you are gettign an EPE of 15ft. You hide your cache. The GPS marks it down, but it's coordinates are actually 15ft north of the cache. Now, the cacher's gps with the same EPE will be led 15ft north of the cache. Actually, with his 15ft EPE he could be led 15ft further north, a total of 30ft north away from the cache.

This most likely won't happen, but it is possible.

15Tango · Posted: Tue Jan 20, 2004 3:48 am Post subject:

My "Down in the Valley" cache is down in a valley, with nearby high-tension wires, and I always get complaints about the coordinates--every time I've gone to do maintenance, my GPSr has been with 20-30 feet. My hiding technique helps out my accuracy--I'll scout out a location, mark the coords in my GPSr, then go home, write my cache page, assemble the cache, then go hide it with a different sat. constellation. If I'm within 10-20 feet, I'll consider everything good to go, if not, I'll come back a few more times and change the coordinates to whatever average I get.
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There comes a time in every young boy's life when he gets an irresistible urge to seek buried treasure.--Mark Twain

Marsha and Silent Bob · Past MnGCA President Joined: 02 Sep 2003 Posts: 6261

Arcticabn · Posted: Tue Jan 20, 2004 9:46 am Post subject:

Yea SB, that's why you were using all that foul language when you were looking for the GPS Knowledge Challenge Cache right. You did good. I guess I only heard 15 or 20 swear words per point on the course. Laughing

We need to do it again.
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Airborne All the Way!

Marsha and Silent Bob · Past MnGCA President Joined: 02 Sep 2003 Posts: 6261

murph · Posted: Sat Jan 24, 2004 4:34 pm Post subject:

As a previous poster said I pretty much turn mine off when I get to the area. Or I sometimes will find a open spot from trees and lay it on the ground and wait a bit.

murph