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Guest chipveres

Golf Ball Averaging

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Guest chipveres

I just found a cache I was having trouble with. GPS unit indicated 25 ft. accuracy, degraded under huge tree where cache is. Dropped a golf ball 25 ft. west of ground zero. Same north, south and east. Cache was within 3 ft. of the intersection of lines between golf balls.

 

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Chip the Big Folk

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Guest k2dave

I'm not sure what you are trying to say. My best guess is that you are using the golf balls as a form of averaging and/or using them in a place where you can get a better lock to help you find a cache.

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Guest chipveres

Exactly right. It's both a form of averaging and a way to get a better signal.

 

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Chip the Big Folk

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Guest Tissue

Great idea! I tested this out in my front yard and it seems to work pretty well. I got me within about 5 feet every time. When ground zero was about 30 feet off. Can't wait to try it on a cache hunt.

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Guest mick92646

Can someone post a little bit greater detail on this technique - or a URL to a site that explains it in more detail? TIA

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Guest Prime Suspect

Nice idea, but I've rarely been cache hunting where a dropped ball would be visible from 25 feet away. The norm seems to be creek sides and heavy undergrowth.

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Guest Elwood

this sounds interesteing but i have a question, where do u get your ground zero reading?

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Guest k2dave

It is easier to find the spot where you are 25 ft away then the 0 ft away (just because there are more spots 25 ft away then 0 ft)

 

Also most of my caches (all of them come to thing) would not allow the golfball averaging since trees and elevation changes would prevent me from seeing the balls.

 

It still could be useful in the woods (depending on how thick) as you get close and take a bearing you could through the ball in the vinicity on the spot.

 

Also you can use a directional item to point to the cache from a location. When you get a few of them out the intersection should be the cache. This way you don't need to be the exact same distance:

 

-> X

 

/

 

[This message has been edited by k2dave (edited 27 August 2001).]

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Guest chipveres

A try for more detail. I knew the cache must be somewhere under this huge banyan tree. But when I went under, the tree started to block the signals and accuracy suffered. Luckily, it's in a park flat as a table top. So I located a point 25 ft. west of the claimed cache point. Then one 25 ft. east. Now I can eyeball a line between the two marked points. Now locate a point 25 ft. north of cache. Now one 25 ft. south. Imagine a line between these two. The actual cache was about 3 ft. from the crossing of the two imaginary lines.

 

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Chip the Big Folk

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Guest hunter

hey ! why didnt i think of this earlier ! great idea ! and around here for some reason people think its cool to leave used golf balls as a trade, which i completely disagree with. now maybe i would have a reason to rid all these caches of their unwanted golf balls. GOOD POST !

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Guest ClayJar

If you have a Good Enough compass, you can do this without even needing any golf balls. I quite often get close to a cache, shoot a bearing, walk to a point somewhere about 60-120 degrees from the current spot, and then shoot another bearing. If you get a handle on precision compassery, you can triangulate caches without markers; if you get a good handle on distance estimation in varied terrain, you can even get away without the triangulation (but I still like to triangulate, as it gives me a chance to see the area from a wide arc, and it gives my GPSr time to settle as well... not to mention "triangulate" is just a fun-sounding word).

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Guest Elwood

do you triangulate by yourself or with a partner?

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Guest Elwood

do you triangulate by yourself or with a partner?

 

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"Well.... if theres a bright center to the universe, you are on the planet that is farthest from." (Luke Skywalker, Star Wars)

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Guest k2dave

From the double post I guess we can assume Elwood triangulates by himself.

 

(He will probably delete one of his duplicate post and try to make me look like a fool)

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Guest chipveres

tri=three. Clearly one must trianglulate with *two* other people.

 

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Chip the Big Folk

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Guest HomeChicken

quote:
Originally posted by mick92646:

Can someone post a little bit greater detail on this technique - or a URL to a site that explains it in more detail? TIA


Yeah would someone explain this better to some beginners? I still can't understand what it is you guys are saying. and I to would like to get rid of the extra golf balls in caches.

 

 

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Bought a eTrex Legend on 7/24/01

I was part of or placed these Caches

Sun rising over Mt.Rubidoux 3/3

Urban Jungle 3/3

Rising sun over Chicken Coop 5/5

Disneyland Geocaching 1/1

 

Need to rate your own Cache?

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Guest HomeChicken

BUMP!

 

I'm still interested in the way this works..can anybody explain this to a 9 year old mentallity?

 

------------------

Bought a eTrex Legend on 7/24/01

I was part of or placed these Caches

Sun rising over Mt.Rubidoux 3/3

Urban Jungle 3/3

Rising sun over Chicken Coop 5/5

Disneyland Geocaching 1/1

Can You C What I C? 2/3.5

 

Need to rate your own Cache?

Geocache Rating System

 

 

[This message has been edited by HomeChicken (edited 31 August 2001).]

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Guest chipveres

It was easy to find the general location, but hard to find exactly. In general the registerd cache point was under a huge banyan tree and some rocks in a park. Outside the tree the GPS was reporting 25' accuracy. But under the tree accuracy suffered and it led me around in a circle. I marked (golf ball) a point 25' west of the cache. Another marker 25' east. These form one imaginary line, or you could add a string. Then I marked a point 25' north and another 25' south. A second imaginary line. Where the two lines cross is the cache point. The actual cache was located about 3' from the line crossing. Accuracy was improved by averaging 4 points and by receiving stronger signals while not under the tree.

 

------------------

Chip the Big Folk

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Guest Markwell

P>The above illustrations help in finding a cache.

 

Using this to hide a cache is a little more complex and gets to the "Golf Ball" method mentioned by chipveres.

 

If you take readings exactly 25 feet east and 25 feet west, and average those two numbers, you should get a spot approximating the cache's longitude.

 

Then the same can be repeated with the spots exactly 25 feet north and exactly 25 feet south, getting an average of the latitudes.

 

It should also be noted that if indeed you went exactly 25 feet and exactly North, South, East and West (90°, 180°, 270° and 360°) you could average all four points and get a pretty good result.

 

Here's a diagram with points exactly 25 feet away in all directions...

6aAdtsvBtgntivZ6rfEbh2w6lmTc9gvl0166.jpg

 

Notice that if you averaged the north and south latitudes, you get the cache's lat (same for E/W and Longitudes).

 

[This message has been edited by Markwell (edited 31 August 2001).]

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Guest Jors

BTW, The mean (or average) between ANY two points, in any direction, results in a point exactly halfway between the two points. So, going exactly North-South or East-Wes is not important, as long as the distances are fairly accurate.

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Guest Markwell

quote:
Originally posted by Jors:

BTW, The mean (or average) between ANY two points, in any direction, results in a point exactly halfway between the two points. So, going exactly North-South or East-Wes is not important, as long as the distances are fairly accurate.


 

As long as you move in the exactly opposite direction from the cache. Otherwise you get the results below...

 

yA9L5XI+Y-64zVuqz9Rtb4I7-zAVzjb80153.jpg

 

BTW - those coords I'm using in the example are not actual places that I've been to, but they are all exactly 25 feet from the hypothetical cache.

 

[This message has been edited by Markwell (edited 31 August 2001).]

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Guest HomeChicken

Markwell ,,!!

That does it! I don't think anyone could have explained it better. you should keep the images you made . I know it took some time to make them and they did the trick. I can't thank you enough. I tried it out in the front yard and seems to work so-so, I think I'll keep to just searching the area like I've been. But thanks for your know how for the time

 

------------------

Bought a eTrex Legend on 7/24/01

I was part of or placed these Caches

Sun rising over Mt.Rubidoux 3/3

Urban Jungle 3/3

Rising sun over Chicken Coop 5/5

Disneyland Geocaching 1/1

Can You C What I C? 2/3.5

 

Need to rate your own Cache?

Geocache Rating System

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Guest Kerry

In theory the "Golf Ball" averaging principle sounds practical but without hindsight it's really still an unknown quantity (similar to averaging) and time will/can/might/does change the whole result.

 

The following image shows the difference between a real world (what actually occured in the field at the time) application (basically done concurrently) using high order GPS equipment compared to the type of equipment generally used for caching along the lines of averaging/interesting cardinals (similar to the "Golf Ball" method).

 

Hopefully the diagram/comments will be self explanatory?

 

1085_1.jpg

 

The position solution of the handheld is still well under SPS accuracy specs but the "integrity" of the solution is the unknown. Also note the "consistent" relative accuracy for the handheld positions but the overall difference to the actual real world position.

 

If one looks at Arffer's "Repeatable Accuracy" diagram's (in other posts) then maybe if I had come back a few hours latter and did the same exercise with the handheld the result would have probably been entirely different? It's an unknown and in practice the perceived position could have been that distance (or further) in the opposite direction? basically any direction? Nobody really would know unless there is something to compare it to?

 

Jut a bigger image of above http://www.cqnet.com.au/~user/aitken/gps/1085.jpg

 

The point is all the theories are fine but in practice one simply can't be sure of what's happenning at a particular time.

 

With GPS systems $$$ not only buys accuracy "capability" but the integrity to especially "know" the actual accuracy of the result. The $$ difference in being able to eliminate the position error (as above) with integrity is huge.

 

Cheers, Kerry.

 

 

[This message has been edited by Kerry (edited 31 August 2001).]

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Guest Markwell

icon_biggrin.gif Kerry - how did I know you'd chime in like this? icon_wink.gif I know that empirically, the data may show that manual averaging doesn't really add too much to accuracy (or precision? - I can never keep that straight), but anectdotally, I can say that I do get better readings with my hides when I manually average. Maybe it just makes me feel better.

 

As for the images, I had made the triangulation ones for my in-laws back in April, and now had a chance to use them. The circles with the averages are new today, but didn't take that long - I'm a geek (and an ex-teacher). cool.gif

 

I'll leave them up here with a link to my AOL site for as long as I'm around.

 

[This message has been edited by Markwell (edited 31 August 2001).]

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Guest Markwell

icon_biggrin.gif Kerry - how did I know you'd chime in like this? icon_wink.gif I know that empirically, the data may show that manual averaging doesn't really add too much to accuracy (or precision? - I can never keep that straight), but anectdotally, I can say that I do get better readings with my hides when I manually average. Maybe it just makes me feel better.

 

As for the images, I had made the triangulation ones for my in-laws back in April, and now had a chance to use them. The circles with the averages are new today, but didn't take that long - I'm a geek (and an ex-teacher). cool.gif

 

I'll leave them up here with a link to my AOL site for as long as I'm around.

 

[This message has been edited by Markwell (edited 31 August 2001).]

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Guest Kerry

face="Verdana, Arial">quote:


Originally posted by Markwell:

icon_biggrin.gif Kerry - how did I know you'd chime in like this? icon_wink.gif I know that empirically, the data may show that manual averaging doesn't really add too much to accuracy (or precision? - I can never keep that straight), but anectdotally, I can say that I do get better readings with my hides when I manually average. Maybe it just makes me feel better.


 

icon_biggrin.gif Hindsight maybe icon_wink.gif That example was only done a couple of weeks ago just for my own interest but as it turned out it does highlight what does/can occur. One thing users have to come to grips without SA is the position solution can stay fairly stable (as that showed) over a short period of time. It wanders much more slowly due to the condition or conditions that are influencing the accuracy (without SA).

 

By doing what I had done there the solutions actually looked fairly good, relative and consistent (as they plotted up) but also consistently off the real world true position of the mark.

 

Doing it that way probably does make one feel better as one is at least attempting to eliminate/check gross errors but as that example shows how do you really know?

 

Cheers, Kerry.

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Guest Kerry

face="Verdana, Arial">quote:


Originally posted by Markwell:

icon_biggrin.gif Kerry - how did I know you'd chime in like this? icon_wink.gif I know that empirically, the data may show that manual averaging doesn't really add too much to accuracy (or precision? - I can never keep that straight), but anectdotally, I can say that I do get better readings with my hides when I manually average. Maybe it just makes me feel better.


 

icon_biggrin.gif Hindsight maybe icon_wink.gif That example was only done a couple of weeks ago just for my own interest but as it turned out it does highlight what does/can occur. One thing users have to come to grips without SA is the position solution can stay fairly stable (as that showed) over a short period of time. It wanders much more slowly due to the condition or conditions that are influencing the accuracy (without SA).

 

By doing what I had done there the solutions actually looked fairly good, relative and consistent (as they plotted up) but also consistently off the real world true position of the mark.

 

Doing it that way probably does make one feel better as one is at least attempting to eliminate/check gross errors but as that example shows how do you really know?

 

Cheers, Kerry.

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