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How Far Off Is Too Far?


drames
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I recently was looking for a cache out in the desert/sagebrush found in my area. I looked and looked but was having no luck at all. I looked in a circle with a radius of about 30'. I was about to give up when I decided to follow part of the cacher's description of it being in line with 2 different posts. I finally found it and my GPS (Magellan Meridian Platinum) showed I was off the mark by 69'! I sat for awhile letting it average but it didn't change significantly. Is this much error normal? I've been 10 to 15' off before but never this far.

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its not uncommon for your GPS to be 30 feet off. Forget what the EPE states. Its not uncommon for the Hiders GPS to be off 30 ft.

that could lead to a 60 foot error. A lot depends on then number of Sat's in the sky, weather. Beer consummation. and several other factors.

 

So while not common, it is possible.

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I wouldn't say 69 ft off is "normal," but I would also not say it was unusual.

 

Anything within 50 ft is within normal tolerances. I've been FTF on many caches where the coordinates indicated on my gps differed from those on the page by over 100 ft; the worse coordinates were off by over 1/2 mile. I suppose "how far is too far" is really determined by the potential number of hiding places in an area and how much time and effort one wants to expend on the cache.

 

There are so many variables that determine the accuracy of coordinates at any given time, on any given day. These forums contain a lot of useful information on the subject.

 

its not uncommon for your GPS to be 30 feet off. ... Its not uncommon for the Hiders GPS to be off 30 ft.  that could lead to a 60 foot error.

Actually, I recalling seeing several mathematical models in these forums over the years that suggest that scenario would lead to a potential error of 45 ft.

Edited by BassoonPilot
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Although I understand the idea of circular probable errors (your GPSr is off 30 ft, as well as the hider's GPSr being off by 30 ft, resulting in a 60 ft error), I have only rarely experienced this much combined error. In my experience, limited as it might be, caches I have found, are within less than 25 ft of the posted locations. In the instances where the found location has been greater than 25ft, I have either listed my found coords, or at least mentioned that I found it xx distance from the posted location.

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I did one today that ended up being almost 200' from the listed coordinates per my own dingus. I put most of the blame on my GPSr, which can occasionally throw off a wild result (but got two other caches dead-bang today). But I'm pretty sure the hider was off, too, mostly because his reported position didn't look right on the topo map.

 

My more general experience is to assume if my GPSr says it's more than 50' away, I'm probably in the wrong spot.

 

I can think of one occasion were coordinates posted in a user log saved me from a heartbreaking DNF. If you have high confidence in your coords, make a tactful mention of them in your cache log.

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I finally found it and my GPS (Magellan Meridian Platinum) showed I was off the mark by 69'! I sat for awhile letting it average but it didn't change significantly. Is this much error normal? I've been 10 to 15' off before but never this far.

You are using a Magellan Meridian, so you probably weren't off the mark or experiencing error. The coordinates to the cache were most likely not taken very carefully. It's not unusual to find coordinates that are way off, this happens when the hider hastily records them so that they can quickly leave the area after the hide.

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A lot depends on Beer consummation.

Beer Consummation: What two beers do after the wedding.

Beat me to it.

 

Back on topic. 69 feet ain't all that bad. When I'm struggling to find a cache I will expand my search to about 100 feet or more before giving up. Like I said, 69 feet not terrible but it is something that the cache owner should rectify ASAP.

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I just did a quick scan of your finds, and think I found the one you were having the problems with. In this case, a couple previous finders had posted their own coordinates, indicating similar positional errors. It's hard to say if the hider was the only one that was experiencing difficulty, or if everyone is. While it appears the terrain is fairly flat, it's hard to say what sort of problem the nearby high voltage power lines are causeing. I noticed that the one set of coordinates posted by other finders is 74 feet away from the original, while the other set is 108 feet off, but they are 46 feet away from each other. One other thing that could be a factor is that it appears the person who hid the cache, and one of the people who posted different coordinates may be using older units only accurate to two decimal places.

Edited by Searching_ut
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I would suggest that a good way to decide on your search radius is to set your GPSr up to show you the accuracy. Walk around the site and note the largest number at any point within about a 20 ft circle of the point where you zero out. Now double that number. The resulting cicle has some fairly high probablility of containing the cache (I would guess something like 90 or 95%). But even then, there is still a small probablility that the cache is outside the circle. And this assumes that the manufacturer is being honest about the accuracy level.

 

Also remember to be thankful that this accuracy is not very small (e.g. 1 ft) because that would take away the challenge and make the whole thing uninteresting.

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