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CundL

...get the most accurate coordinates?

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Hi! :)

 

We want to place a cache (our first one) and already found a very nice spot, a good hiding place and a container that fits very well. Moreover, we've read and unterstood the guidelines and are aware of the rules.

 

However, we took the coordinates three times with our GPS (Garmin) and every time got - of course - slightly different coordinates. To see which coordinates would be most accurate we tried them out in Google Maps and Bing. And we were really suprised to see that...

...in Google Maps the coordinates we got from our GPS are about 30 meters walking distance from our anticipated hiding place where we took the coordinates.

...in Bing the they are closer to the anticipated hiding place but still not really at the correct spot.

 

What should we do? Should we publish the coordinates we took with our GPS or rather trust Bing or Google coordinates and take them from there?

 

Thanks in advance for your answers!!

Greetings from Germany

 

CundL

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DO NOT trust the coordinates from the Internet! What type of Garmin GPSr do you have? Many of them have the option to do waypoint averaging which records and averages a series of readings over time. You could average the coordinates for a minute or more and probably get the best results. If you do not have this option on your GPSr, then you can take 15 different readings a minute apart and average them all together, you'll have a better set of coords than if you take one reading and leave.

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The way I was taught was to back off 30 or 40 feet from the cache and then walk up to the cache, let the GPS settle down as much as possible, then write the coordinates down. Repeat this from all four directions then average the last three numbers of the coordinates.

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Here's the method I use. Some might think it's overkill but this is what I do...

 

1. Turn on your GPS at GZ and allow 5-10 minutes or so for it to acquire satellites and settle.

2. Move away from GZ approx 20m (or 60 feet) then return to GZ. Allow the GPS to settle and take a reading. Write it down.

3. Repeat step 2 in a different direction from GZ.

4. Complete this procedure a total of six times, in six different directions. You will now have 6 readings.

5. On another day, (could be 1,2,3 or more days later) complete the above procedure again as the satellites are now in a different position. You will now have a total of 12 readings.

6. On a third day, complete the above procedure again. You will now have a total of 18 readings.

7. Any readings that are way off, disregard. Average the remaining readings. This will give you a set of coordinates for GZ.

8. On a fourth day, test the set of coords you have come up with.

 

Using this procedure you should now have a set of coordinates that are as close to accurate as possible. I have never had to adjust the coordinates on any of my caches due to inaccuracies after employing this method.

 

Good luck with your task.

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...we've read and unterstood the guidelines and are aware of the rules.

You may have read the guidelines, but I am not so sure that you really do understand them.

 

I say so because of this question.

What should we do? Should we publish the coordinates we took with our GPS or rather trust Bing or Google coordinates and take them from there?

 

The first line of the Technical Requirements section says:

Listings must contain accurate GPS coordinates.

You will notice that Bing or Google are not words contained in that sentence.

 

It is good that you ask first (some don't bother even to do that).

I would say that you should check to make absolutely sure your GPSr is set to the correct Datum and Format: WGS-84 and HDD(D)° MM.MMM .

It probably is, but re-checking certainly won't hurt.

 

Other posts (already added) pretty much delineate proper procedures. Averaging is good, but add to that TIME. To rush out and take (singular) readings is not good. Take your time, allow the unit to settle in. Multiple readings over several days is best, but not absolutely necessary.

When averaging, toss out the obvious wild readings before doing your calculations, if your unit will not average them for you.

 

Cannot stress enough that time is a necessary ingredient. Rushing to get it done does not help.

 

Wishing you well on your first hide. Work hard and do it well. It gets easier with practice.

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Averaging with readings over time. Different times of day - different days is the best method. Averaging readings in a single session though will either give you roughly the same result as a single reading or if the sats are in poor geometry overhead - you just average together bad data. You just don't know which. I have found that a single reading after letting the unit settle down is often every bit as good as a single session averaging.

 

Never rely on the online maps - I know one local area where the maps are a good 30 meters off. The published accuracy of those maps is usually no better than 10 to 15 meters. You unit is far more accurate most of the time. Sometimes they are spot on - trouble is you never know for sure.

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Thank you geoCATing for the hint with the averaging option!! Our GPS does have it. :)

 

And thanks a lot DonB, Calypso62, Gitchee-Gummee and StarBrand for sharing your experiences and methods!!

We'll give them a try and hopefully find out the most accurate coordinates like that! :) (And we'll no longer let us unsettle by Google/Bing!)

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Thank you geoCATing for the hint with the averaging option!! Our GPS does have it. :)

 

And thanks a lot DonB, Calypso62, Gitchee-Gummee and StarBrand for sharing your experiences and methods!!

We'll give them a try and hopefully find out the most accurate coordinates like that! :) (And we'll no longer let us unsettle by Google/Bing!)

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However, we took the coordinates three times with our GPS (Garmin) and every time got - of course - slightly different coordinates.

How different? .001 is equal to only 3-6 feet, depending on your latitude. Considering consumer GPS only claims accuracy of 30 feet, or 10 feet with WAAS, I wouldn't worry about a difference of .001 or .002. Just average your 3 readings together and go with that.

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Most newer Garmin units will do waypoint averaging. What I usually do is this:

 

1. Take a reading using the Averaging function. When you start to take a reading you should get some sort of accuracy meter that shows the unit's "confidence" in its accuracy. Just put the unit down somewhere and watch it until this meter goes full scale. The reason I say put the unit down is to eliminate any possible movement on your part, and also to make sure your body isn't blocking any of the satellite signals. The unit should take a minute or two to achieve maximum confidence. Accept this reading

 

2.Go back another day and repeat the above procedure. Your Garmin should have a way of starting with your original waypoint that you saved and adding another averaged reading to the same waypoint. No need to do the math manually.

 

3. Perform this procedure for at least 3 or 4 days.

 

4. Finally, using the waypoint you have obtained, use it to navigate back to the cache location. Does it put you accurately at GZ? You're good to go.

 

Don't worry if your coordinates don't match up exactly with Google maps or any other online maps. In some places those maps are known to be off, sometimes incredibly so. Get good readings and trust the device, not the map.

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Most newer Garmin units will do waypoint averaging. What I usually do is this:

 

1. Take a reading using the Averaging function. When you start to take a reading you should get some sort of accuracy meter that shows the unit's "confidence" in its accuracy. Just put the unit down somewhere and watch it until this meter goes full scale. The reason I say put the unit down is to eliminate any possible movement on your part, and also to make sure your body isn't blocking any of the satellite signals. The unit should take a minute or two to achieve maximum confidence. Accept this reading

 

2.Go back another day and repeat the above procedure. Your Garmin should have a way of starting with your original waypoint that you saved and adding another averaged reading to the same waypoint. No need to do the math manually.

 

3. Perform this procedure for at least 3 or 4 days.

 

4. Finally, using the waypoint you have obtained, use it to navigate back to the cache location. Does it put you accurately at GZ? You're good to go.

 

Don't worry if your coordinates don't match up exactly with Google maps or any other online maps. In some places those maps are known to be off, sometimes incredibly so. Get good readings and trust the device, not the map.

 

Well, I do #1 and #4 and have never had a problem. My 60CS is on long before I arrived so it should be warm and have a good lock. I let it sit for about five minutes and then I hit Mark, then AVG. Then, I set it down, or prop it against something small so the antenna is pointing up, then I walk away from it for at least a minute. Probably the biggest mistake that I see people do is hover over their GPSr while it is averaging, essentially blocking half of the sky with their body. After I come back and save the waypoint, I walk 50 to 100' away and tell my GPS to bring me back. If it doesn't, I start over. I have hidden a lot of caches and the only time I have ever had a complaint is for the one that I took readings on more than one day and then averaged on paper.

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On their website Garmin suggests both single and multiple session averaging. For single session they state 7 to 10 minutes is the recommended time to let the GPS sit. They say the most accurate results are obtained by averaging on different days.

 

Since OP wanted "the most accurate" the multi day method is the way to go. However I agree in most conditions a single long session will work just fine. In areas of dense tree cover or where signals are reflected off buildings or cliffs making follow up visits to get different satellite geometry is usually worthwhile.

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