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Accuracy

 
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FreeS



Joined: 07 Mar 2005
Posts: 6
Location: Manitoba

PostPosted: Mar 20, 2005 4:00 pm    Post subject: Accuracy Reply with quote

I've been wondering if the brand of GPSr makes any difference in coordinates. I've read some logs on geocaching.com where one person says, "the coord's were dead-on", and a few logs later another cacher says the cache was 12m off. Is this dependent on conditions or on the different GPSr's?



For those of you who set up caches in tough conditions (e.g. under dense trees), what are some methods of getting accurate coordinates?

-- Edited by FreeS at 10:47, 2005-03-20

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Gumpy



Joined: 12 Mar 2005
Posts: 13
Location: Winnipeg

PostPosted: Mar 20, 2005 10:13 pm    Post subject: RE: Accuracy Reply with quote

I kind of answered this one on my other post.

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TheStuntman
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PostPosted: Mar 21, 2005 12:04 am    Post subject: RE: Accuracy Reply with quote

If there is a clearing close to the cache it's a good idea to get a distance and bearing then pace it in to the cache. I've had to do this for a few different caches and it seems to work.



I noticed that P Mclure even mentions this little tip when doing his Lockport East cache.



The-Stuntman



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FreeS



Joined: 07 Mar 2005
Posts: 6
Location: Manitoba

PostPosted: Mar 21, 2005 7:20 pm    Post subject: RE: Accuracy Reply with quote

Would this also be the best way to set up a cache? I'm planning on doing a cache come spring, but I'm actually a little scared of posting slightly off coord's, since my Magellan doesn't always seem consistent. I've had to turn it off and then on again before to get a proper signal, even in an open area like the "Rivers Collide" cache.

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TheStuntman
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PostPosted: Mar 21, 2005 7:44 pm    Post subject: RE: Accuracy Reply with quote

If you read the how to's at geocaching.com, when setting up your cache, they explain that you should take a half dozen readings and average them out to get better accuracy. Walk in on your cache sight a few times to check it against yourself.



The-Stuntman



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Peter and Gloria



Joined: 06 Mar 2005
Posts: 254
Location: N50 00.___ W96 57.___

PostPosted: Mar 23, 2005 10:20 pm    Post subject: RE: Accuracy Reply with quote

There are many things that affect accuracy. Sun Spots; time of day; snowing ; wet leaves; tall building; metal structures.



I read somewhere that if you have various GPSr's sitting togther that there is a good chance they would all have the same reading, but that if you came back later to the same spot with the same GPSr's, they could quite easily all have a different readings.



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1Queenand4Jokers



Joined: 07 Mar 2005
Posts: 270
Location: Manitoba

PostPosted: Mar 24, 2005 2:28 pm    Post subject: RE: Accuracy Reply with quote

Joker 1 usually lays the GPS right on top of the cache in a forested area or on a day when the signals are jumpy and lets it rest for a minute or so and then marks the spot. He does this 2-3 times and then we average the readings (if they are within reason). Then he walks away and circles it at a distance to see if the arrow points toward the cache. It most often does. If not he tries again. We always walk away and try to find it ourselves.



 



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junglehair



Joined: 05 Apr 2005
Posts: 374
Location: Winnipeg

PostPosted: Apr 08, 2005 3:04 pm    Post subject: RE: Accuracy Reply with quote

A couple things to keep in mind when placing a cache.



1)  Let your GPS settle first before marking the spot.  20 seconds or so should be good, just so it has a solid fix on it's location.



2)  Check the accuracy at the time you place the cache.  If you have a clear view of the sky, and the satellites are in good position, your accuracy can be as low as 7 or 8 feet.  If that's the case, you can mark the cache once and walk away - you're probably not going to get any better coordinates than that.



3)  Ideally, you would get readings at different times of the day, since the location of the satellites determines the accuracy, and use the average of those readings.



I usually mark the location, walk about 50' away, go back and mark it again.  I do this a couple of times to see if I am getting consistent readings.  If the accuracy is 30' (10 meters) or greater, you might consider going back at a different time of day and trying again.



Even if you had absolutely perfect coordinates, it's going to depend on the number and location of the satellites the GPS is receiving when the person goes to look for it.  That is why some people report that the coords were dead on, and some say that they were off by 30' or more. 



If I find a cache that is 50' or more from the posted coordinates, then I usually take a reading with my GPS and post it on the cache page. 



Hope that helps.



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