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# Accuracy Of Coords When Hiding

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Recently, I have seen some discussions about how different people take coordinates when they place a cache. I decided to do a simulation of various scenarios in order to be able to quantify the effects of GPS accuracy, averaging, etc.

So I wrote a Monte Carlo program that simulates taking coordinates. I defined the "accuracy" of a GPS measurement as the 90% confidence interval; that is, if you take a measurement with a given accuracy, 90% of the time you will be closer than that distance to the true coordinates. This is not identical to the way that the GPS vendors define their accuracies, but it is reasonably close.

So here's the first graph: What's the probability of coordinates you measure being a distance away from the true coordinates? Here you go:

The two curves are for 20 and 30 foot. You might be surprised to see that the most likely distance is about half of the accuracy (as I defined it). Why isn't the probability of being closer to the true value greater? It's because there isn't as much area in the circle closer to the true point!

A better way to look at this data is as cumulative probabilities, as shown in this graph:

Here the curves show the probability of being closer than a certain distance from the true value. As you can see, the 90% mark is at the accuracy for both curves.

--- continued ---

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So why is it so important for the hider to have good coordinates? Here are some examples:

Here the line is the probability that the finder, who has a GPS with an accuracy of 10 feet, will be within a given distance of the cache given various errors in the hider's coordinates.

As you can see, if the hider's coordinates are off by 15 feet, the chance that the finder will zero out within 5 feet of the cache is essentially zero. If the hider's coords are off by 25 feet, the finder is completely out of luck. There's very little chance he will zero out closer than 20 feet from the cache.

So, based on this data, I would say that hiders should always try to get better than 10-foot accuracy. But how can you do that when you can't get enough satellites?

Simple. Average several measurements. For those measurement errors that are random, averaging is very effective. Here's a graph that shows you:

As you can see, good averaging can make an enormous difference in the quality of the hider's coordinates.

So how should you average? The basic idea is to try to minimize the non-random component of the error, which won't average out. Take a measurement (averaging for a while if you have a GPS that will do it, like a Magellan or a Garmin 60), then move 100 feet away from the spot, and move back, and take another. Then move away in a different direction and come back for a third measurement.

Ideally, you should come back to the spot after a reasonable amount of time has elapsed (a half-hour or so) and re-take the measurements.

I also recommend using WAAS if your GPS has a decent implementation of the WAAS algorithm (the newest firmware for most units is good).

I've noticed that as geocachers get more experienced, the coordinates of their hides improves. The quality of your coordinates says a lot to other geocachers about how much effort you put into your hides, and how much you care about their experience in finding your cache.

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Simple. Average several measurements. For those measurement errors that are random, averaging is very effective.

GPS errors are not random and averaging gives absolutely NO guarantee that the final positions will be more accurate.

Cheers, Kerry.

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I no longer average (did it for the first 5 or 6 caches) and my coordinates are just as good now, as they were when I averaged. I rarely receive complaints about my coordinates and in fact often get compliments.

If you're not getting a good sat alignment, or signal, you're just averaging bad data. If you come back over several hours, or days and one of your readings is bad and the rest are good, you're throwing off your good coordinates by averaging.

I find it to be a waste of my time. If I do receive complaints, I'll just go back and try again, but I've only had to do this twice out of 70+ caches I've placed (and one of those two I averaged).

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GPS errors are not random and averaging gives absolutely NO guarantee that the final positions will be more accurate.

I should have known when I posted some valid technical information Kerry would find some way to post misinformation just to be contradictory.

He is almost completely wrong, folks. There is a portion of the GPS error that is not random, but it changes over time in such a way that it can be minimized. Averaging is a frequently-used tool to improve position accuracy. What's particularly amusing about Kerry's little statement above is that he has frequently pointed out in the past that extensive averaging must be used in order to obtain centimeter-accuracy GPS positions. So he's even contradicted himself.

You don't have to trust me. Here are a few references:

CPC Spatial Analysis Unit

GIS Development paper

Actual Data

I purposely didn't get into an even more complex discussion about systematic versus random errors and how they apply to GPS readings, because I wanted to give information that would actually be useful to people.

I can now see that I wasted a significant amount of time for nothing.

Forget it.

Edited by fizzymagic
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Fizzy, wait a second, we still have questions, don't shut it yet!

1) In our local forum, people argued that while the idea of averaging is great, it may be mis-implemented by cachers. Basically what people might do is to move 100 ft in a certain direction, return, click, repeat. It was argued that a GPSr doesn't settle yet, but the standart instructions don't tell you how long you have to wait after the 100ft back-and-forth. Which is probably model-specific and dependent on actual precision?

2) Outliers happen and as it was correctly pointed earlier in this thread, outliers are resulting in problems with averaging. Should we recommend medianing instead? Is there any way to access accuracy of waypoints after they were recorded, in order to use a weighted averaging or medianing technique (i.e. low-accuracy points will be gived much reduced weight) ?

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Averaging may be good, but as Brian said, if you don't have good sat geometry when you are averaging, you're just averaging bad data.

Conversly, if I happen to look for a cahce when the DOP is high, it won't matter how good the hider averaged his cache coords.

Here is an example of DOP values for a particular time period at a certain location. Obviously, if I were hunting a cache when the DOP values were spiked, it would be impossible to zero out on the cache location.

Here is a graph of the same location/time period, but I have added obstacles (top image) to create the effect of being under heavy tree cover (tall firs). You can see the effect it has on reception. Moving around in the trees may give you better accuracy, but as we know that doesn't help in zeroing in on the cache. Knowing when you will be able to get the best accuracy at a particular time/location is really what will help you to be assured that the coords for your own cache are correct.

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I should have known when I posted some valid technical information Kerry would find some way to post misinformation just to be contradictory.

He is almost completely wrong, folks. There is a portion of the GPS error that is not random, but it changes over time in such a way that it can be minimized. Averaging is a frequently-used tool to improve position accuracy. What's particularly amusing about Kerry's little statement above is that he has frequently pointed out in the past that extensive averaging must be used in order to obtain centimeter-accuracy GPS positions. So he's even contradicted himself.

I purposely didn't get into an even more complex discussion about systematic versus random errors and how they apply to GPS readings, because I wanted to give information that would actually be useful to people.

I can now see that I wasted a significant amount of time for nothing.

Forget it.

For s start Fizzy "extensive averaging" is really not what allows centimetre accuracy (as such) not in your context anyway. This is fact not a contradiction, just that one needs to understand the difference between the two.

But yes "extensive averaging" in your context/understanding of averaging does reduce possible errors. 95% of all possible eroors can be averaged out in 24 hours, 99.99% of all errors requires about 30 days. Simply not feasible from a preactical point of view is it.

Information that is actually useful to people is what actually occurs in the real world and really you've only wasted your time if you can't accept the facts based on actual data.

Basically there appears this thinking that one only has to average and presto the coordinates will be better. Sure they can be better BUT they can also can be worse and which way the pendulum swings for someone averaging is a toss and people have to realize this and not simply average for the sake of averaging, it doesn't always work but it does work about 50% of the time, the other 50% of the time it simply doesn't.

The point NavDog makes with obstructions and geometry is also valid and especially with obstructions there is almost infinite possibilities.

Affect of Obstructions on Averaging inn the real world

More on Averaging in the Real World

People need to decide for themselves if averaging today without Selective Availability, in obstructed environements etc is actually viable and all the technical theory in the world doesn't replace on the ground data. To simply average for the sake of averaging most people are simply fooling themselves as quite frankly without hindsight they wouldn't have a clue if the coordinates are better ot worse.

Cheers, Kerry.

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Basically there appears this thinking that one only has to average and presto the coordinates will be better. Sure they can be better BUT they can also can be worse and which way the pendulum swings for someone averaging is a toss and people have to realize this and not simply average for the sake of averaging, it doesn't always work but it does work about 50% of the time, the other 50% of the time it simply doesn't.

You don't know much statistics, do you?

Your statement above that averaging gives worse answers 50% of the time is totally, completely, 100% wrong. Period. If you don't even know enough basic math to understand how averaging works, how should anyone expect that you can give them decent advice on how to use their GPS?

In actual fact, taking a second point and averaging it with the first has a substantially higher than 50% chance of improving the measurement, as long as a significant amount of the error is suitably random on the time scale between the measurements. For handheld GPS measurements, there is enough short-time-scale variation that this is true.

Edited by fizzymagic
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I no longer average (did it for the first 5 or 6 caches) and my coordinates are just as good now, as they were when I averaged. I rarely receive complaints about my coordinates and in fact often get compliments.

I don't think I've ever averaged a cache placement and my results are about exactly the same as Brian's.

I have a 4% no-find rate where a container was actually in place. Probably half that or less is due to bad coordinates.

All the discussions regarding statistics and averaging methods, present and past, are very interesting but I haven't seen a practical application for it in geocaching as yet.

The average geocacher doesn't average their placement coordinates and I still find their caches.

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I'm curious if one only takes one reading how do they know that one is not an outlier?

I do take the time to take several readings. I take about 6-8 reading with walking away about 30', coming back and letting the unit autoaverage for about 30 seconds before making a waypoint. The readings I get can differ by a few thousands of a minute. These I average together, but through out the wild outliers.

I'm curious how to know any one of those readings is more accurate than all of them averaged together while throwing the wide readings?

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Like I said if averaging feels good then do it and some can argue all day about that but without taking into full account the actual characterics of GPS behaviour then some of the thinking and comments about random behaviour is off base.

GPS behaviour is neither random or predictable with respect to Service Availability, Service Reliability and Accuracy, which must all be taken into account for the result to mean anything. The vast majority of the time the track is reasonably constant in rate but variable in direction and with SA discontinued over the period of time some recommend to average the end result simply can't be guaranteed as being better.

A GPS position solution simply does not jump all over the place but basically has a slow undertermined track and this is where many get caught up in the averaging myth and especially now that SA is discontinued.

Cheers, Kerry.

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I have only set 5 caches, but this is what I usualy do, especially on the multis, where there are several waypoints and the cachepoint:

I take several readings of coords on several days, sometimes with both my Garmin and Magellan. With about 10 readings, I look at the result and usually there is a "mode" or most common lat and long. coord. So, I throw out the high and low readings and use the mode, or reading that makes the most sense, given the EPE on those days, etc.

Nothing real scientific/statistica; more of a judgement on the best coords to use.

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The one thing that leaves averaging for dead these days is actually being in the required location at the BEST time. What's the point of going to all the trouble of going to a location just to have to work with crap geometry and expecting averaging is going to fix bad geometry, high PDOP etc.

Also take the current position rate of change now that Selective Availability is discontinued. This is something like 4cm per second or around 2.4 metres over 1 minute. So even if the position is tracking closer towards the absolute real world position (which one doesn't know anyway, either the absolute position or the track trend for better or for worse) then if one averages for 1 minute the maximum affect on position assuming a straight track can be no better than 1.2 metres and considering the display precision of just about every handheld then in reality it's a waste of time.

Cheers, Kerry.

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I have only set 5 caches, but this is what I usualy do, especially on the multis, where there are several waypoints and the cachepoint:

I take several readings of coords on several days, sometimes with both my Garmin and Magellan.  With about 10 readings, I look at the result and usually there is a "mode" or most common lat and long. coord.    So, I throw out the high and low readings and use the mode, or reading that makes the most sense, given the EPE on those days, etc.

Nothing real scientific/statistica; more of a judgement on the best coords to use.

EScout, what you are doing it exactly what I recommend! Blind averaging is better than none, but even better is to do as you describe, where you take several readings separated by a couple of minutes, moving around between each one. I sometimes even plot them on a map to look for a grouping, or choose a best average by eye.

The whole purpose is to get the most reliable coordinates you can. As I said before, I notice the difference in the quality of coordinates taken by careful, experienced geocachers (like Marky, for example) and those taken by cachers who obviously just casually pushed the "Mark Waypoint" button once as they placed the cache.

How careful each hider is in taking coordinates is, clearly, up to them. Especially for urban hides, or places with many possible hiding spots, I think high-accuracy coordinates are essential. If I place a well-hidden cache, I want the difficulty to be in finding the cache, not in guessing how far off the coords are. I've even seen a couple of cases where hiders used bad coords as a cheap and easy way to make their caches more difficult to find. I suspect you can imagine my opinion of those hides.

All that said, the essence of my original post stands:

• Geometric factors make it most likely that a single measurement of the coordinates of a point will be off by about half the accuracy reading or more.
• Bad coords make it nearly impossible for the finder to zero out in the right spot.
• Averaging multiple measurements is overwhelmingly likely to give a better result.

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I feel smarter for having just read this thread !

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I feel smarter for having just read this thread !

You look smarter too

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... to average the end result simply can't be guaranteed as being better.

Kerry,

You've always made sense in the past, but now you're scaring me!

I understand the electronic position and the real world position rarely coincide. It is only close with the various error correcting schemes. As a little experiment a while back I waypointed the end of my couch and then did a goto to that waypoint. I could mentally visualize the electronic position drift around me. 8' that way. 3' that way. It's like a bouy with an elastic anchor rope.

Now, I can agree with the above statement. The first reading could very well be dead on, the actual spot. Further readings and averaging them could pull the coords off. I can see that.

However, I think the crux is this. What is the likelyhood of any one reading being more accurate than several readings averaged together?

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As I stated earlier, I do not average because I've found no benefit. I don't disagree that averaging may sometimes give you better coordinates, but is it really beneficial to spend several hours over several days (as some suggest) to obtain coordinates that are 5 feet off instead of 15 feet off? For those who think it worth the effort, great, but a lot of us have better things to do with our time.

I just went through a few of my cache logs at random and came up with the quotes below. I could easily find a lot more. These came from caches where I just casually pushed the "Mark Waypoint" button once when I placed the cache.

"We circled back and Bingo!! Within 6 feet. Great hiding job"

"Today the GPS’r guided me to within 7’ of a very likely hiding spot. I quickly found the cache "

"I found it after about a 10 minute search, just about 10 feet from where the GPS said it should be"

"Found it quite easily due to excellent coordinates; I had 2' ro 3' at the cache."

"I slowed as I approached and the needle was reading 5ft when I found the cache."

"The GPS’r put us within 10' "

"Brians coordinates were dead on as usual"

"The second stage wasn't much trouble either, being out in the open, the coordinates were right on. "

" Bushwhacked over and found the prize with no difficulty. GPSr had us within 8 feet."

"In retrospect, my GPS was very accurate on this one. I just refused to believe it..."

"We got to the site at 11:30 AM. The coordinates were right on."

"We basically followed the GPS’r arrow to within a few feet of the cache and Nicole found the prize in less then a minute."

"Briansnat's coordiantes were right on the money"

"I found the first stage quickly, the numbers were dead on."

"The coordinates were incredibly accurate, so the cache was a super-easy find"

"The gps got down to 0'/0 xte for a while right at the high spot near the cache."

"The GPS’r indicated less then 10’ at the cache location."

Are there logs where people said my coordinates were off? Sure, a few, but they were often for the same caches where my coordinates were praised by others. This leads leads me to believe that it was conditions at the time that affected many of their readings.

So my method is good enough for me and seems to be sufficient for most of the people who find my caches. I'm not saying don't average. Go right ahead if you insist. But while you're making your 3rd or 4th visit to the cache site, you could be out there placing or finding another one.

Edited by briansnat
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Well, then that makes me very curious how anyone could have wrong coordinates. You take an eTrex Vista and "casually" mark a waypoint, yet there are caches 50-100 off. How's that?

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I have only set 5 caches, but this is what I usualy do, especially on the multis, where there are several waypoints and the cachepoint:

I take several readings of coords on several days, sometimes with both my Garmin and Magellan. With about 10 readings, I look at the result and usually there is a "mode" or most common lat and long. coord. So, I throw out the high and low readings and use the mode, or reading that makes the most sense, given the EPE on those days, etc.

Nothing real scientific/statistica; more of a judgement on the best coords to use.

An "A" for effort but by the time you place your 20th cache you should be cured of this habit.

Earlier I said that I didn't average but actually I always punch the "average" button and let it run for a min. of 30 seconds and often much longer. I don't come back at the point multiple times or on different days.

We all are using more than just coordinates to find caches. We ask "Where would a hider place this cache? What is the obvious feature? Where are the parallel sticks, stump, stack of rocks?". When Spark and I cache together she usually finds the location first by asking these questions and I am somewhat hindered by the gps. When I call out we are within 100' to 50' she almost always finds the spot.

The problem caches are those where the terrain doesn't have obvious features such as dense brush or landscaping. As placers we then have an obligation to give enough clues to prevent people from causing damage. The best coordinates averaged by any method can't pinpoint the cache because of the PDOP variation the day the finder arrives.

We don't even need to talk about city micros in this discussion because a placer will never know if the signals that do get through are bouncing off walls and giving false readings.

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An "A" for effort but by the time you place your 20th cache you should be cured of this habit.

Team Sagefox:

If you were to attempt my "Shoreline Triangle", rated 4,3, with 3 waypoints to find in a triangulation to the cachepoint, you would be glad I have precise coords.

For simple one-stage regular caches, going through this extra effort may not be as necessary.

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However, I think the crux is this. What is the likelyhood of any one reading being more accurate than several readings averaged together?

Maybe think about it this way. Over a period of time the position track will create a cob web affect and roughly the average of many readings (the minimum spec is 24 hours) will/should approximate close to the actual real world position, give or take a bit.

To create this cobweb effect the position solution really has to spend half the time going one way and half the time coming back.

Over a short period of time and at the rate of change of the position solution now that SA is discontinued it really doesn't go all that far in a short period of time. The position solution now that SA is discontinued is quite stable and one reason why differential stations don't really have to transmit corrections every second or two and could transmit a correction every 10 seconds etc has not a lot changes in this time frame compared to the required end result.

So if say the first position is say 5 metres north and the position solution tracks north (4cm/sec) for the next 60 seconds and your averaging then your position will technically be 6.2 metres off and worse then the first original position. Of course if it just happened to be tracking south then the position would be 3.8 metres and better.

There is absolutely no way that the position solution is by some magical method always tracking closer to the absolute position. Half the time is basically spent wandering out and the other half wandering back again and this is where short term averaging fails completely and has no integrity as to if the end result is better or worse. It's really a lucky dip.

The thing is you don't know which way the position is tracking relative to/or the absolute coordinates.

Cheers, Kerry.

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Well, then that makes me very curious how anyone could have wrong coordinates. You take an eTrex Vista and "casually" mark a waypoint, yet there are caches 50-100 off. How's that?

The world average system spec is less than 43 feet 95% of the time, there another 5% that is unknown (more than 43 feet). The worst case scenario is less than 118 feet at 95% again there is an unknown 5% that "could" be more than 118 feet.

Accuracy, geometry and many conditions in general that affect accuracy are in fact quite variable and barring the "affect of the user" on accuracy all that is quite possible especially considering the system accuracy specs (43 and 118 feet etc) is actually Signal-In-Space accuracy before the user does what some users do.

There can be many many reasons and really in some cases there's an appliance thinking that is applied with GPS where some believe it's always perfect and one only has to point and push and it has to be right.

For a period of time a position could certainly be off by any number and there is some classic examples of quite large distances for quite long period of times and unfortuneately the unwary wouldn't pick this up and if one was averaging a group of position solutions that were 40km off then the end result is simply going to be 40km incorrect as well. There's no magic formula where a set of incorrect position solutions suddenly become correct.

Cheers, Kerry.

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For those interested in what the other 5% can/could/might look like then THIS IS WHAT CAN ACTUALLY OCCUR

This is really an extreme example but it is real and there's nothing stopping similar scenario's within what might be classed as difficult to detect at the time.

Cheers, Kerry.

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There's no magic formula where a set of incorrect position solutions suddenly become correct.

True, but if my actual X coord is "0" and I take one reading and it says "5" then I am off by 5.

If I average the following:

5

6

4

5

2

1

-6

-4

-3

0

3

then my average (that I post) will be the total (11) / the number of readings (11) = 1. Pretty darned close - better than "5".

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Yes Dave, one scenario of many and many is really an understatement. The Dynamic nature of GPS basically eliminates anything actually occuring exactly again.

So how about

5 4 3 2 3 4 5 call that 3.7, better than 5.

2 3 4 5 4 3 2 call that 3.3, worse than 2

One could come up with what ifs all day but one thing is for sure the track nature is not predictable but neither is it random.

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nature is not predictable but neither is it random.

Gee, there will sure be a lot of physicists surprised to hear that!

It is often wise to not keep digging the hole deeper, Kerry. Your comments about the averaging process betray a deep misunderstanding of statistics as well as a misunderstanding about how GPS devices work. I wasn't going to say anything more, but I can't let this last comment stand, since it is also completely wrong.

Your "example" above is ridiculous; how likely is it that you could take 5 measurements of a zero-valued quantity and get no negative numbers? About 1 in 32, as it happens. I think the problem you might be having here is that distance is a vector quantity, not a scalar. Two measurements that are each 2 meters off will tend to average to a measurement closer to the correct value because the direction of the two measurements is important, too, not just the magnitude.

BTW, what's really cool about quantum mechanics is that the Universe really is random!

Edited by fizzymagic
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Fizzy, if you are going to quote someone then stop trying the smartarse trick and quote the whole context not your selectiveness.

One could come up with what ifs all day but one thing is for sure the track nature is not predictable but neither is it random.

BTW your also appear to have a little bit of selective tunnel vision especially when it comes to discussion regarding replies in the original context of the original poster.

You can continue to push crap up hill with a stick all day but at least make sure why your pushing it. Are you tring to say GPS position solutions are random, your a bigger fool than I thought.

Cheers, Kerry.

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So what does everybody associate as the "nature" of GPS position solutions over some generic time frame, Plot 1 or 2?

Cheers, Kerry.

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Here's how I do the dastardly deed. Hopefully, this will serve to simplify the quest for accuracy.

I take a waypoint, once. I go online and using both terraserver.com (for pay) and Microsoft's Terra-server (free), I plug in the co-ordinates I obtained. I then compare real life, as seen from the photo, to the co-ordinates. If my co-ordinates are off, I'll simply get a better one from the pictures.

Simple and extremely accurate. Unless, of course, both terraserver.com and terraserver-usa.com are both inaccurate. :-)

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Since my GPS has auto-averaging, I will leave my GPS on the cache for 5 minutes, take it out of averaging, and then let it average again for 15 minutes.

Watching the coordinate screen, the numbers have stopped changing after those 15 minutes. At that point I'm done.

The coordinates have been properly averaged and the result is a dead nuts reading.

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Psstt... a little secret here, this is a GAME.

I am not sure that it would be all that much fun if I would just plug in the coordinates and be taken to within centimeters (or inches if playing in the USA) of the cache. That is like taking the persons hand and leading the right to the cache, what fun is that?

This is a very interesting thread, and the knowledge presented here is very extensive and informative. If I was intending on surveying property, or trying to aim a cruise missle down your chimney it would be very helpful. It is almost frightening what some people here know. I have to remember never to argue mathematics or logic with you people.

But the reality of it is that this is a game, and yes it is helpful if the coordinates are fairly accurate, but if they are off then what? Is someone going to sue me for time lost looking for my cache if the coordinates are off a bit? God forbid I slow someone down on their numbers game by having them take a little extra time to find our cache rather than drive or walk right to it.

We try to be accurate when hiding our caches, we average positions, look for areas of good cover but then also try to be a little sneaky when hiding it, that is part of the fun. And besides, who is to say that the person who finds and then replaces my cache puts it back EXACTLY in the same place? I really do not care if EVERYBODY can find every one of our caches, some people may not be able to find them, I expect that and will check them if we get a DNF notice to ensure that they are still there.

With our caches now, we try to use the coordinates to bring you to an area, then use clues to solve the puzzle. It seems to work well, and the logs that we get on our caches indicate that the finders enjoy the puzzles.

Thanks again for the great info, and remember, it is just a game.

CP

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Well said.

Why is it most threads degenerate to simply rudeness?

Don't answer that, anyone - it's off topic :-)

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Well, I went back and read this article which is a later version of the one that convinced me to buy the SporTrak series.

Reading carefully it says something that confirms what cachew nut says. In the article they are able to get sub meter accuracy on a fairly repeatable basis by letting the unit average for 30 minutes.

I hadn't read that article in a while and it seems to me that I could have been saving myself a lot of work by following CN's method! Just put the sucker down for a few minutes, break the averaging, and then let it sit again until settles down completely. Simple. Yeah, yeah, it depends on coverage and geometery, I know that.

This probably means that just grabbing a few readings in a few minutes doesn't do any good, but it certainly doesn't confirm that averaging is no good! Actually, it means that averaging IS beneficial, but only if you do it right. Nor does it mean Fizzy's project is useless. In fact, if you are taking the time to get more accurate reading, then it's beneficial to the finders!

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If my co-ordinates are off, I'll simply get a better one from the pictures.

I can't imagine getting coordinates for a cache that I've hidden from a picture on terrasever.

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I read this article http://users.erols.com/dlwilson/gpsavg.htm about the benefits of averaging right after I got my Garmin GPS III+. This predated geocaching.

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Reading carefully it says something that confirms what cachew nut says.  In the article they are able to get sub meter accuracy on a fairly repeatable basis by letting the unit average for 30 minutes.

I hadn't read that article in a while and it seems to me that I could have been saving myself a lot of work by following CN's method!  Just put the sucker down for a few minutes, break the averaging, and then let it sit again until settles down completely.  Simple.  Yeah, yeah, it depends on coverage and geometery, I know that.

I realized the benefit of having a WAAS averaging GPS only after researching how to properly use my GPS. It took some practice and trial and error.

When I arrive a spot and watch the coordinate screen, I notice that the numbers are still changing since the GPS (Meridian Gold) is still performing the averaging calculations. These stop in a about a minute or two, I always allow 5 minutes to be safe. That is when I break the averaging and start over, since I want to throw out the previous readings. The new averaged readings are taken fresh, with no previous data from the time I was on the move. It seems to work well and apparently accurate and repeatable.

Edit:typo

Edited by cachew nut

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