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Marking a Cache's Position


Kyle_freemason

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Hello everyone,

 

I have been out finding caches recently and found that my new Garmin etrex legend hcx is superb. The coordinates on the geocache website were very accurate. Every cache I nearly stood right next to based on the coordinates given. My question is, when I mark a spot in my yard and try to return to that exact spot I find that I am often up to 20 feet off -- Is there any tricks/secrets to getting a more accurate reading while marking the spot of the cache? I know inherently the gps will not typically be accurate enough to bring someone right to the exact spot of my cache, however, I would like to give them the most accurate coordinates possible. Any ideas, hints, tricks or tips? Thanks a bunch and happy caching!

 

Kyle

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Hello everyone,

 

I have been out finding caches recently and found that my new Garmin etrex legend hcx is superb. The coordinates on the geocache website were very accurate. Every cache I nearly stood right next to based on the coordinates given. My question is, when I mark a spot in my yard and try to return to that exact spot I find that I am often up to 20 feet off -- Is there any tricks/secrets to getting a more accurate reading while marking the spot of the cache? I know inherently the gps will not typically be accurate enough to bring someone right to the exact spot of my cache, however, I would like to give them the most accurate coordinates possible. Any ideas, hints, tricks or tips? Thanks a bunch and happy caching!

 

Kyle

 

That is an excellent thing to show concern about! Building a reputation for providing tight coordinates on your hides is important.

 

Your HCx is capable of waypoint averaging. While there are strong opinions (with good arguments) on both sides, I have had very good luck by averaging. I will typically run a minimum of 200 samples, and then I will walk well away from there, and "test" the coordinates. Sometimes they'll be right-on, and other times I'll have to repeat the procedure until I get something that I'm satisfied with.

 

Remember that when you're averaging, you're also averaging in any errors, so be sure to take enough samples to smooth out any artifacts.

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20 feet is good. And that matches about the average accuracy of these handheld units.

 

You can use the built-in "averaging" function to try and improve your readings (get about 50 or more) - but the simple fact is that if your sat readings and accuracy are poor - you are just going to average bad data. Better method is to return to the spot several times over a few days (different times of day) and then average all those readings. However, that is only marginally better. Many will tell you the best method is to just let the unit sit there and sort of "settle" on the location (10 to 20 minutes) - then just take a single reading and let it be.

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Hi,

 

Thank you for your response. I was not aware of the fact my gps had the waypoint averaging capability. How do I do this? As for wanting to give someone the best coordinates possible, I like everyone else like to have as much fun as possible and would like to think that the person who hid the cache had my best interest in mind. So for that very reason I want to be as accurate as my unit can be capable of so that the cacher has the best chance of finding the cache possible. I am curious to hear more about this waypoint averaging and how to do it. Thanks again!

 

Kyle

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Hi,

 

Thank you for your response. I was not aware of the fact my gps had the waypoint averaging capability. How do I do this? As for wanting to give someone the best coordinates possible, I like everyone else like to have as much fun as possible and would like to think that the person who hid the cache had my best interest in mind. So for that very reason I want to be as accurate as my unit can be capable of so that the cacher has the best chance of finding the cache possible. I am curious to hear more about this waypoint averaging and how to do it. Thanks again!

 

Kyle

 

When you mark a waypoint, the button on the left will start the averaging. It will take one sample per second and display the *estimated* level of accuracy (don't put too much stock in that voodoo number, though!).

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... Is there any tricks/secrets to getting a more accurate reading while marking the spot of the cache?...

 

Not really.

 

If you take coords every time you re-visit your cache and average those over time, that would tend to start becoming more and more accurate.

 

That said, even with perfect coordinates, any one visiter could still be 20' off on the day they stop by your cache for exactly the reason you were 20' off when you came back.

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I do not mind the inaccuracy of the gps units, I just wanted to get as close to the correct coordinates as possible. I wish our civilian units were equally accurate to those of the military. I think theirs are capable of centimeters if what I read was accurate. I have noticed that some of the caches I have found recently have had pretty good coordinates, others were pretty far off (while my unit was stating it was getting 10ft of accuracy). I wonder if the cache was placed on an overcast day or by a receiver that was not waas enabled? Possibly it was just the old 12 channel receiver? Anyway, thank you guys for all of your replies!

 

Kyle

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I do not mind the inaccuracy of the gps units, I just wanted to get as close to the correct coordinates as possible. I wish our civilian units were equally accurate to those of the military. I think theirs are capable of centimeters if what I read was accurate. I have noticed that some of the caches I have found recently have had pretty good coordinates, others were pretty far off (while my unit was stating it was getting 10ft of accuracy). I wonder if the cache was placed on an overcast day or by a receiver that was not waas enabled? Possibly it was just the old 12 channel receiver? Anyway, thank you guys for all of your replies!

 

Kyle

You have a number of assumptions in this message that are just not true.

 

In general, ALL of our handheld units average about 20-25 accuracy most of the time. WAAS makes things better but only if you get a WAAS sat and only works if both hiders and finders know that and both use WAAS. The frequencies for GPS were specifically chosen beacuse cloudy conditions do not affect the signal. Almost all newer Garmin units are still "12 channel" receivers. The accuracy as reported your unit isn't too be taken as "golden" - it is an EPE (Estimated postion Error) and only has a confidence of 75% or much less. Next time try reading it as "I think there maybe a 50% chance that we are within 10 foot of the actual coordinates". Military and survey grade units do much better but are far more expensive and require more time to use. Fact is, conditions at any site change with time. The "spread/geometry" of the sats overhear has much to do with determining the accuracy. Your 15 accuracy when hiding might be a 30 ft accuracy to one searcher and a 6 ft accuracy to another. All searching the same spot within hours.

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I see what you mean. I did try the average feature on my gps. I put out two items in my yard. One spot I let the gps sit ontop of the item for about 5 minutes and then marked its position. The other object I allowed the gps to sit ontop of it but this time I used the averaging feature. It seems that the averaging worked a bit better but there was not a remarkable difference. I did find both of these methods to be much more accurate than simply marking the waypoint without allowing for the gps to "sit" for a while before marking.

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Here here on the unit averaging in garbage....sometimes it just happens.

 

Although the only time it has happened was with the automatic averaging function on my "new" GPS. It could be because the "new" mapping GPSr I'm using now (which is actually and older non-H etrex legend, while my "old" no-frills GPS is a newer regular old H-etrex) doesn't do as well near trees...or maybe it's because I've haven't turned WAAS on...or maybe it's just chance. But the one time I used that feature......it was off by more than I'm used to when placing a cache.

 

Always got pretty good coordinates taking three points and manually averaging them with the old one. The automatic averaging...ehhh...not so good.

 

The scientist in me wants to do more testing with both. But I just want to cache.

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I place my gps where I am going to place my cache then set about getting it ready to hide, discuss name for cache write in front of book etc. Basicly just put down in the spot I want the cache for about 5 minutes before marking the spot.
This is a very important step! In fact, when I do this the averaging value seldom changes from the reading I get after letting the GPS settle in for five minutes.
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