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Tips On Creating Good Coordinates?


geowego

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Okay, I know I have seen a topic like this in the past and a search for it has turned up nothing so I'll state my case. Lately a few of my hides have had people looking 30 to 50 feet from where my cache is hidden given the coordinates I have listed at the site. My GPSr which is a basic yellow Garmin eTrex has been very reliable to me. Although I did notice that when I was creating my coordinates I could not lock an accuracy rating better than maybe 25 or 30 feet. I would usually get around 16 or even 14. And this would be on a clear sunny day with no trees or buildings around to obstruct my view of the sky.

 

So basically my question is this...

 

Is it best to take your coordinates directly where you plant your hide since most GPS's will not give the same 100% accuracy as other's or should I continue to take them a few yards away from the cache as I have been?

 

And second, is getting your accuracy the lowest you can better for creating your coords or is 25 to 30 feet still ok?

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Is it best to take your coordinates directly where you plant your hide since most GPS's will not give the same 100% accuracy as other's or should I continue to take them a few yards away from the cache as I have been?

 

And second, is getting your accuracy the lowest you can better for creating your coords or is 25 to 30 feet still ok?

Yes you should take the coordinats from EXACTLY where you hide the cache or as reasonably close as possible to obtain a sat reading. If you are a "few" yards away - say so on the cache page - something like "cache is 5 yards north of posted coordinates".

 

Getting an average error rate of about 25 to 30 feet with a non WAAS unit is very good and about as good as you can expect.

 

It is normal (common) to have to seach for a cache within 20 - 40 feet of where your GPSr "zeros" out. Keep in mind that your readings may have had a 30 foot error and the searchers GPSr might habe a 30 foot error and that leaves the cache 60 foot away.

 

No worries - sound like you are doing ok.

 

edit for fast typing

Edited by StarBrand
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We use an etrex as well.

Our technique is to move away from the cache about 30ft is or to some nearby clearing and walk SLOWLY back to the cache, hold the gps above it for awhile and mark the waypoint.

Now move off in another direction and repeat try to do this from four sides of the cache.

Go home and using the excell averager (on our website) find the average of the co ordinates you have taken.

The important thing is to move slowly and allow the gps to settle above the cache

Hope this helps !!

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I started with a yellow etrex and placed my first hide with it. I got a little carried away though. I went back 6 times (3 different days & times) and approached the location from N, S, E, W then averaged all the numbers and posted what I got. Now I have a GPS 60 and I have hidden several with it. It allows you to average the location and has given fairly good results. I let it average for about 30 minutes. And it all depends on the type of hide & location - micros, desired good readings, regular-large not that critical. If you are in doubt on your numbers provide good information on the cache location or post a spoiler picture of the cache location. Once I get close to the cache location I find MY ground zero and begin the search from there. I have found one within 2 feet of where I set my GPS down and the other was 7 feet (both micros), that is the closest I have ever come a majority of them can be found within 20-30 feet of the posted numbers if good readings were taken at first.

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The best way to get the best accuracy on the coordinates of your cache, short of extraordinary effort, is to take your fix when the satellites are in the most favorable configuration. The accuracy or EPE reading on your gpsr is the only convenient way you have of telling how good the satellites are at a particular time.

 

But there is a way of maximizing your chances of being there when the satellites are best. That is to use satellite prediction software. Trimble has a bloated (Windows application) program to do this, which I've long since removed from my computer. My preferred program is from Leica Geosystems.

 

Here's a screen shot of the Availability/DOP page for today in your area. The best times are at the minimums of the blue line, though any time GDOP is less than 6 will probably be fine for hunting. Less than 3 is nice for placing a cache. But to get the actual numerical value of GDOP when you take a fix, you would need to write down the satellites you're actually receiving at the moment, and then edit the page to exclude all others from the calculation. The accuracy reading from your gpsr is a rough indication of this.

 

This chart shows right around 2pm PDT is the best time this afternoon.

 

082d4629-fb0c-428b-8c98-549a2ed7c52b.jpg

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Okay, I know I have seen a topic like this in the past and a search for it has turned up nothing so I'll state my case. Lately a few of my hides have had people looking 30 to 50 feet from where my cache is hidden given the coordinates I have listed at the site. My GPSr which is a basic yellow Garmin eTrex has been very reliable to me. Although I did notice that when I was creating my coordinates I could not lock an accuracy rating better than maybe 25 or 30 feet. I would usually get around 16 or even 14. And this would be on a clear sunny day with no trees or buildings around to obstruct my view of the sky.

 

So basically my question is this...

 

Is it best to take your coordinates directly where you plant your hide since most GPS's will not give the same 100% accuracy as other's or should I continue to take them a few yards away from the cache as I have been?

 

And second, is getting your accuracy the lowest you can better for creating your coords or is 25 to 30 feet still ok?

On my GPS I can about 200 readings and average them on my Vista C. I get good comments for the accuracy of the coords. There are ways you can average coordinates even if you cannot do it on your GPSr.

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If you have access to a National Geographic Topo map series, you can pick out a feature and go there and mark it with your GPS, then come back and download onto the map, to see if they mesh. You can do the same with Topozone. I dropped a cache at a feature and used it as first stage of a multi, on the cache page when the Topozone opens I can see if it is within range. Recently I saw some back and forth over a cache where marks were 100 to 170 feet off on each of a 5 part multi, the owner blamed the equip.

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On the few hides we've done, we've tried to get as accurate as possible with the GPSr. Then, at home, we've looked up the coordinates on an online map (Google Maps, for instance) - zooming in to the maximum. Then we try adjusting the coodinates on the map until the arrow centers on the cache location. (For instance, if the arrow seem too far east, we increase the west coordinates .001 degree, and continue from there.)

Edited by Sugar Glider Sweatshop
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After getting the best coordinates that I can using most of the above mentioned techniques I'll do a final check using my magnetic compass. I'll move off at least 60 to 80 feet preferrably to a spot with a good view of the sky and after allowing the unit to settle down do a "find" or "go to" the cache. Noting the bearing degrees to the cache I'll dial it in on my compass and if it then points to the cache hiding spot then I know my coords are pretty good. I'll repeat this from 2 or 3 different spots. Maybe it's overkill but I feel a lot more confident afterwards.

 

Olar

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Also, you can use USAPhotomaps to help verify your coords. Plug them in and look at the Sat view. Finders of our caches have done this to show us when we were a little off. Now I plug the coords in on all of our new ones, and we've gotten praise for the accuracy of our hides.

 

Good luck,

 

- T of TandS

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Have you tried standing on the cache location and turning off your gps and then turning it back on? I wonder if that would give a more accurate reading...

 

I tried it this weekend on a "disposable" waypoint (marked location of marina on the lake so I'd be able to find my way back to shore) and the numbers seemed to be right on.

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Thanks everyone for contributing to my questions! Lately I have been getting good locks on my satellites and am averaging about 14 - 16 feet accuracy with my GPS'r. This has given me a big plus on setting my waypoints. Occasionally I have my accuracy at around 30 feet or so but I notice then that I don't have very good satellite reception. Thanks again!

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I simply set my Magellan Sportrak down where the cache will be and when all satellites are in effect with WAAS let it sit for about three to five minutes. Then write the numbers down so there is no disputing where I was.

 

Dont be surprised though if people go find your cache and say it is 20 feet off because their system isn't using the same amount of technology as yours is.

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