How Close is Close?

October 27, 2003

I've noticed that some cachers seem to get a "bit upset" that posted coordinates do not lead them to within a few feet of a cache. how close is close???

[This message was edited by instep_guy on October 27, 2003 at 09:10 AM.]

24.7k · October 27, 2003

20' is close.

30' is close enough.

After that you might want to consider posting coordinates in your log.

Generally I'll do it if the coordinates are 50' or more off.

October 27, 2003

thanks for the info!

October 27, 2003

Well, it should be within the error of the setter's GPS plus the error of the finder's GPS. So, with a good skyview and WAAS on both units you could get within 10 feet?

Somewhere with tree coverage, hidden and found by someone with a basic GPS will probably only get within 100 feet, worst case.

Cheers,

Stu

October 27, 2003

quote:
Originally posted by Stu & Sarah:
Well, it should be within the error of the setter's GPS plus the error of the finder's GPS. So, with a good skyview and WAAS on both units you could get within 10 feet?

SNIP

With a good sky view and WAAS most consumer GPSr have an accuracy rating of 3 meters. If you use your formula of 3 meters plus 3 meters you get just a bit more than 19 feet, 8 inches.

4 or 5 meters is more realistic, with a clear sky and WAAS info. 13 to 19 feet each.

If you don't have WAAS capability, or coverage, then you can widen that to 10 to 15 meters each. A Garmin basic Etrex, for example, states 15 meters (49 feet) accuracy. Without WAAS reception all of the Etrex line is about the same.

20 feet is right on--less than 30 is fine. If your GPSr agrees +/- .005 minutes of angle, that is a coordinate match.

On my caches I regularly see finders post cordinates with their log that are .001 or .002 different from those on the cache page. I simply ignor them.

When my GPSr nulls out, I put it in my pocket and start looking. If I don't find the cache within 30' or so, then I'll recheck my readings.

Another common mistake is not letting your GPSr actually null out. When you get to a point where you read less than 5 to 10 feet you should let your GPSr stabilize for at least 3 to 5 minutes to improve your fix.

The GPSr is to get you close to the cache location. You still have to look for it. I have talked to several cachers who started out expecting to get to a point where there GPSr nulled out and see a cache sitting straight under it. It doen't take long for most people to get past that level.

Dave_W6DPS

My two cents worth, refunds available on request. (US funds only)

October 27, 2003

I'm pretty happy to be within 50'...besides the fun is looking for it right? I have yet to ever be right on top of it. That would take away the adventure in my opinion.

38.2k · October 28, 2003

Anything under 50 feet is fine and normal. I may say something if the cache is 75, or more feet off, but I never blame it on the coordinates of the cache owner. It could be because of my GPS reception on that day.

Now if there are numerous logs complaining about the coords being off, the owner should take the hint and re check them.

"You can't make a man by standing a sheep on his hind legs. But by standing a flock of sheep in that position, you can make a crowd of men" - Max Beerbohm

5.9k · October 28, 2003

For me it depends on the satellite reception in the area of the cache. In a canyon, I’m thrilled with 30 feet. On a high mountain peak, I better be seeing single digit EPEs. Interpolate for yourself.

http://fp1.centurytel.net/Criminal_Page/

October 28, 2003

Well, being new to this...and watching various wars on TV, I thought GPS was accurate to the foot. I know have a better understanding of why GPS bombs sometimes miss...but then again, I guess for a 2000lb. bomb...30 feet is a direct hit!

1.4k · October 28, 2003

Close enough for Horseshoes, hand grenades and ammoboxes.

"Me transmitte sursum, Caledoni!"

1.7k · October 29, 2003

I find that many caches around here are within 12 feet of where my GPS points.

I have never posted "corrections" in a found log, but I will make mention if my GPS is 20 or more feet off. I don't presume it is the hider's error. It may be mine, or the tree cover.

DustyJacket

Not all those that wander are lost. But in my case...

October 29, 2003

quote:
Originally posted by DDG:
Well, being new to this...and watching various wars on TV, I thought GPS was accurate to the foot. I know have a better understanding of why GPS bombs sometimes miss...but then again, I guess for a 2000lb. bomb...30 feet is a direct hit!

Military GPS accuracy for precision munitions is a whole different matter. Additionally, many munitions such as the cruise missile use a combination of visual data and GPS. They are pretty accurate.

October 29, 2003

30 to 50 feet has always been good enough for me...

******************************************

* Remember... Only you can pervert forest faeries... *

******************************************

Official H2G2 Researcher #248886 www.pdxgeocaching.com

**Namaste**

October 29, 2003

There's a caching team in our area that hides alot of caches. Their coordinates always bring me to within singal digits but close to me is twenty feet or less.

November 3, 2003

The goal is to take me to the spot, stop, look at my feet and see the cache. Anything under 10-20 feet accuracy is sloppy cache placement.

I always post my coordinates to show where I found it, whether at ZERO ZERO with the placer or 6 feet off. It is a mind game, and accuracy counts.

I have noticed that people using Magellan Meridians are usually more accurate than the Garmin crowd. Any ideas why that occurs?

Never underestimate the stupidity of people in large groups.

1.4k · November 4, 2003

The goal is to take me to the spot, stop, look at my feet and see the cache. Anything under 10-20 feet accuracy is sloppy cache placement.

You're kidding, right?

Jeff

http://www.AlaCache.com

http://www.StarsFellOnAlabama.com

http://www.NotAChance.com

1.7k · November 4, 2003

Originally posted by Scott Johnson:
The goal is to take me to the spot, stop, look at my feet and see the cache. Anything under 10-20 feet accuracy is sloppy cache placement.

QUOTE]

Close to me is finding the cache, or its location if it's been trashed! That means finding it anyway I can, if I can't find it ,then how do I know if I'm close or not, when I've not got a clue were it is.

Dave

I burn to cache!

November 4, 2003

I like it when the accuracy is messed up, tree cover and a cliff or a canyon or a river gulley. If fact, I just built a multi where I purposely "watered down" the 2nd of 3 coordniates. I placed the "point" about 70 feet from the actual cache, and gave this as instructions. Truth in advertising is great, this way nobody goes home crying, unless they try to look in the river in the winter...

<b>Mf

I¦like¦nachos¦&¦I¦miss¦John¦Cash.

<i></b><center>got coordintes?

http://www.esg.montana.edu/gl/usa1d.html

http://terraserver.homeadvisor.msn.com/AdvFind.aspx

http://www.geocities.com/mfrenchy2002/GEO.html

please see¦GCGX7T

November 5, 2003

Well, error estimates are not a guarantee, they are merely a statistical quantity. You CANNOT say "SURELY I will be within x meters from the point". An EPE of, say, 5 meters simply says "you have X% of probability to be within 5 meters from the stated coordinates". EPE is not a simple error estimate, nor do the producers relase the level of confidency (that X%) of their algorythm. I estimated that Garmin EPE (state as "accuracy" in the eTrex) has to be somewhat around 66%. Let's say it's OK. This means that in one case over three, your position will be NORMALLY off more than 5 meters.

As has been said, the actual distance from the cache dipends also on the error in the posted coordinates. In fact (let's be a bit pedantic) the two errors do not simply sum, because the two GPSr would have been generally off in different directions. The most correct estimate of the cumulative error would be to sum the squares of the two errors and then take the square root of the sum (Pythagoras)... you obtain a final error smaller than by simply summing the two. But again you will be "inside" the error only two times over three.

Two or three times in a year I saw my eTrex yellow (no WAAS) boasting a 4 m accuracy. Assuming that also the cache placer had been so lucky, this would give 5.65 meters of cumulative error, slightly more than 18 feet. With WAAS and the best possible conditions (3 m) you would in no case go below a final 14 feet. And again, you will be in fact outside this distance one time out of three. Considering that typical conditions rise EPE to something between 5 and 7 m (no WAAS, no heavy cover) final errors between 23 and 32 feet are much more realistic estimates of what you may expect.

This does not mean that you cannot stomp over the cache when your GPS says "zero". Means that you are merely luck if this happens, and that you may not assume wrong coords when you find the box 15 meters from where the toy zeroed...

Ciao

Acaro of Team_TAR

November 5, 2003

If my GPS reads zero feet I then assume that the hider may have been off by 30 feet then assuming that I may be off 30 feet I search a 60 foot radius. This usally does the trick for us!

Camping Hoosiers

Memphis, Indiana. USA

3k · November 5, 2003

quote:
Originally posted by Camping Hoosiers:
If my GPS reads zero feet I then assume that the hider may have been off by 30 feet then assuming that I may be off 30 feet I search a 60 foot radius. This usally does the trick for us!

If I remember correctly, if the gpsrs of both the searcher and the hider had potential errors of 30 feet, you would need to search a 45 foot radius. (But I thought the standard for handheld gpsrs was 15 meter accuracy, which would be more like a 73 ft radius to search. Glad that most gpsrs seem to be more accurate than that!)

Somewhere in the forum archives are some excellent graphs and illustrations from a previous incarnation of this discussion.

November 5, 2003

quote:
Originally posted by Scott Johnson:
The goal is to take me to the spot, stop, look at my feet and see the cache. Anything under 10-20 feet accuracy is sloppy cache placement.

I always post my coordinates to show where I found it, whether at ZERO ZERO with the placer or 6 feet off. It is a mind game, and accuracy counts.

I have noticed that people using Magellan Meridians are usually more accurate than the Garmin crowd. Any ideas why that occurs?

Never underestimate the stupidity of people in large groups.

Oh man, you are cracking me up! You're not the person who did the sock puppet about not wanting to get muddy last week are you?

November 5, 2003

Oops, forgot the most important part of that last posting...

November 6, 2003

quote:
Originally posted by hikemeister:

quote:
Originally posted by Scott Johnson:
The goal is to take me to the spot, stop, look at my feet and see the cache. Anything under 10-20 feet accuracy is sloppy cache placement.

I always post my coordinates to show where I found it, whether at ZERO ZERO with the placer or 6 feet off. It is a mind game, and accuracy counts.

I have noticed that people using Magellan Meridians are usually more accurate than the Garmin crowd. Any ideas why that occurs?

Never underestimate the stupidity of people in large groups.

Oh man, you are cracking me up! You're not the person who did the sock puppet about not wanting to get muddy last week are you?

I don't think he's kidding, in 1 log entry he is complaining about a cache being 55 feet from where it's "supposed" to be. That is a bit high, but nothing to take a tone about. There were others that had coordinate problems on that one too.

___________________________________________________________

If trees could scream, would we still cut them down?

Well, maybe if they screamed all the time, for no reason.

Click here for my Geocaching pictures and Here (newest)

[This message was edited by martmann on November 06, 2003 at 12:45 AM.]

4.1k · November 6, 2003

quote:
Originally posted by Scott Johnson:
The goal is to take me to the spot, stop, look at my feet and see the cache. Anything under 10-20 feet accuracy is sloppy cache placement.

I have noticed that people using Magellan Meridians are usually more accurate than the Garmin crowd. Any ideas why that occurs?

I'm curious, wouldn't it be anything over 10-20 feet accuracy instead of under? I use a Magellan Meridian Platinum and it consistantly gets us within 20 feet of the cache and usually less than 10 feet.

John

*******************************************************

It's hard to remember that your primary objective is to drain the swamp, when you're up to your a$$ in alligators.

November 8, 2003

quote:
Originally posted by team_tar:
Well, error estimates are not a guarantee, they are merely a statistical quantity. You CANNOT say "SURELY I will be within x meters from the point". An EPE of, say, 5 meters simply says "you have X% of probability to be within 5 meters from the stated coordinates".... Considering that typical conditions rise EPE to something between 5 and 7 m (no WAAS, no heavy cover) final errors between 23 and 32 feet are much more realistic estimates of what you may expect.

Acaro of Team_TAR

Now that's about the finest explanation of the "real world" of using the GPSr for geocaching I've ever read. As a bonus, we get the theorem. I'm always happy to make a find within thirty feet of the published coordinates. I do, however, post my Magellan Meridian coordinates when I find the coord's in dispute by more than twenty feet. Just to assist the next geocacher who may need something to compare his device with.

"Today's truth remains valid only as long as it withstands the test of tomorrow's discoveries" - George Hicks

November 8, 2003

.. a different perspective.

I have second hand experience with one of my areas top cachers - well over 2000 finds. I'm told he uses a gekko and really only uses the gps to get to the general area of the cache. from then on searches, quite quickly they say. coordinates, shmoordinates. I recently hid a cache and stupidly posted the location of a nearby trail sign i waypointed. it sat for a bit until he went out for it and found it, 150 feet away from the zero point. (yes, i've updated the location.)

for some people, the coordinates are important. for some people, the cache is important. for some people, the surroundings are important. for some people, the numbers are important. for some people the outing is important. it's the great thing about this rash - there's something for everyone.

November 9, 2003

quote:
Originally posted by gallahad:

Now that's about the finest explanation of the "real world" of using the GPSr for geocaching I've ever read. As a bonus, we get the theorem. -

Well, thanks... too kind! It's simply that my work involves a lot of error analysis and estimate, so I'm used to this stuff...

In fact, the theorem and all does not make so much difference. I mean, in the reald world, I look to my error, and, as a thumb rule, expect to be within 1.5 and 2 times that distance from any waypoint I'm looking for.

By the way, have no idea if my estimate of 66% confidence for the garmin EPE is exact: is simply the result of some testing I made. The algorythm Garmin (or any other brand) uses to calculate the error is proprietary, and this isn't strange. The anyway SHOULD relase the confidence figure, because without it the error estimate is meaningless, just like if you say "my error is 15" without telling me if you are using feet or meters.

Acaro of Team TAR

Simia est simia, etiam si aurea gestet Insigna.

2k · November 21, 2003

The very first cache that I hunted for was one in a million in that I did actually walk until the GPS said 1' and there it was right in front of me. If you think about it. This would have made Geocaching much to easy and I am sure I would have quit the sport if this had been the result everytime. If you check my logs you will see that I have logged a fair number of skunks so this is not the case, and I am glad. Sometimes when I am searching and I know the @$#**& thing has got to be there I am not so sure though.

November 21, 2003

Well, being new to this...and watching various wars on TV, I thought GPS was accurate to the foot. I know have a better understanding of why GPS bombs sometimes miss...but then again, I guess for a 2000lb. bomb...30 feet is a direct hit!

The military uses another signal or two that we as the general public don't get. This is why they (the military) are accurate to inches.

Peace!

3.9k · November 21, 2003

I'm super happy if a cache is within 20 feet. On some rare occasions I'll find one within 5 feet. over 40 feet or so I'll mention that either the coords or MY GPS was off by x amount.

1.5k · November 21, 2003

What I want to know is, who do I complain to when my Vista shows 0.0', yet I'm still 50' from the cache ABOVE it? I mean really, the cache owner should take into account altitude and somehow accomodate for it.

1.1k · November 21, 2003

The military uses another signal or two that we as the general public don't get. This is why they (the military) are accurate to inches.

Inches? in this context is a misconception and incorrect.

The Military equiv to the Standard Positioning Service is basically about the same accuracy level.

The second freq simply allows for atmospheric corrections to be corrected in real time instead of from a model.

In the not too distant future there will also be a civilian second (and third) freq, which will basically bring civilan accuracy down to around 1.5 metres but inches no, not even military without augmentation but then that's a different deal again and something civil users also use anyway.

Cheers, Kerry.

November 23, 2003

Wife and I just started geocaching. Been at it since Oct. 21st of 2003. We have found 31 caches. Some the GPS takes us right up to them within 3 feet, others are off up to 30 feet. Or our GPS is off, don't know. We love doing this. Searching around isn't a big deal. Most of the caches if you slowly look around for them you can see them. Others we have to break down and do the hint. But our goal is to find them without doing the hint.

We have hid two caches so far. Did the waypoint and then checked it, both were under 6 feet. Are waiting for someone to go out and find them, log them, just to be sure our coordinates and GPS is right on before we add more.

November 24, 2003

After I was caching 1/2 a year or so, I watched a group of the state's high finders in action.

They approached using their GPSr's, got within 20ish feet and started hunting. Found it!

Whoa!

Then (this was a weekend event), I was caching w/a woman who started when I did. Her style resulted in finding before me more frequently than the other way around. She approached 30' or so, looked toward the most obvious hiding place, "Where would I hide a cache?"

Bam!

Now I use a hybrid, at 20' sometimes I'll even put the GPS down. I head for a likely spot, then start searching spiraling outward. If I come across my GPS, I'll see if it's settled on a totally different area and search over there.

The worst/hardest is a rocky outcrop that induces TONS of signal bounce (hehe, back at that event, several of us headed on top of a knoll, my GPS took me straight into the middle scrub, another's took her to the right edge about 25' away, the other's took her to the opposite edge, about 35' to my left!)

So remember, when a placer does it, such affects are in place, and then you go looking for it--accuracy/epe numbers become irrelevant in the face of reality!

Enjoy,

Randy

November 24, 2003

I'm glad that our very first find was "blackdogs Frog Hollow", a very tough camo job. Gps said 5 feet and we circled for 45 minutes. Tadpole was sitting on it at one time.

But the gpsr said we were there so we didn't give up. The effort they put into the hide was worth every minute of the find. Since then the easy ones aren't so exciting,and it's kind of disappointing when the prize is just sitting there in plain view. Great job Blackdog, I intend to make them work a litte ,too.

How Close is Close?

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