Ensuring Accurate Cache Coordinates

February 23, 2005

How much time do you spend, when placing a cache, to ensure you have the most accurate coordinates possible? I usually walk away in as many different directions as I can and walk back and take a reading. Sometimes I will make a waypoint, walk away, and do a goto back to that WP to see how close I get. Other times I will write down the last three numbers, walk off and back and check the numbers. I keep doing this until I get two or three that match. I feel like I owe it to the cachers seeking my cache to have accurate coordinates. I hate going after caches that are up to 60' off of the posted coordinates. I know there are a lot of variables that will influence my GPS reading. But when I can walk right up to three caches in a row and the next one is 30' off I wonder if they took the time to get those accurate coords. So tell the caching community how you do it.

Red Bear of Spokane WA

38.2k · February 23, 2005

I take about 2 minutes. I make sure my GPS has settled and has a good signal, then I hit mark and use that. At one time I averaged by taking a reading moving away, then going back and taking another (repeat 20 time), but I found little discernable difference in the quality of my coordinates done this way, so I feel its a waste of my time.

Sometimes there is a bad signal and/or poor sat alignment and if you average that, you're just averaging bad data. If you have a good signal and good sat alignent then there really is no need to average.

If I get complaints, I go back and take another reading, but with 111 hides I think I've had to do that maybe 3 times (and one was where I averaged).

20.7k · February 23, 2005

I guess it depends on the location.

If my GPSr claims that it has a good fix (low epe), I just mark a waypoint and move on.

If it is a location that makes it difficult to get a good fix I take more time. Usually, it is as simple as setting down the GPSr and letting it settle down for a little while.

February 23, 2005

Like sbell111, if we have a good fix, then it's almost drop and go.

February 23, 2005

So is a GPSr more accurate moving (slowly) or stationary? I know on mine it states that it is "averaging" when I am still. I always took that to mean a moving target was more accurate because you are getting updated information on your location. Whereas the GPS is sort of "lost" when it is not moving so it has to "average" where it thinks you are. Am I right or wrong? When I have had a good signal strength, walk in, mark a WP, walk off and do a goto back to the WP, I might be several feet off. Am I expecting to much to be able to walk back to ZERO? Just wondering.......

20.7k · February 23, 2005

I think that it is more accurate as it sits around stationary. It is still getting sat updates. I may be wrong, but I think it gets better.

38.2k · February 23, 2005

So is a GPSr more accurate moving (slowly) or stationary? I know on mine it states that it is "averaging" when I am still. I always took that to mean a moving target was more accurate because you are getting updated information on your location. Whereas the GPS is sort of "lost" when it is not moving so it has to "average" where it thinks you are. Am I right or wrong? When I have had a good signal strength, walk in, mark a WP, walk off and do a goto back to the WP, I might be several feet off. Am I expecting to much to be able to walk back to ZERO? Just wondering.......

There is a difference between getting an accurate direction of travel and an accurate reading for marking a waypoint. You want to be moving for the former and still for the latter.

And yes, you'd be expecting a bit much to walk back to zero. Factors as simple as your body position shielding signals will cause minute variations in reception.

18.9k · February 23, 2005

I usually let my GPSr sit on the location and average for about 5 minutes (60C). I then walk away and come back 2 more times and average the 3 averages. Takes about 20 mins but I believe it gives a bit more accuracy (a very little bit). But early on I had one that was about 35 feet off for most visitors and I had just done a drop and go with low EPE. So now I take a little more time.

2.1k · February 23, 2005

For me in part it depends on location. How important are accurate coordinates in that location? How many good hiding places are within you circle of error. If its a lot, you owe it to the searcher to spend some time on it (normally I set down the GPS, and tell it to average out the coordinates for a minute or two). While doing this, if its snowy out, I tend to lay lots of false tracks down in the snow just to make it a little tougher on the FTF.

I'm not really sure that allowing your GPS to 'settle' is going to make all that much difference. How is the GPS going to know that you aren't moving around in a given area? Of course setting down the GPS, and backing away may give it time to really get a good fix in its current location, so maybe that it the real benefit.

I dunno, of course averaging bad data doesn't help much either...

24.7k · February 23, 2005

I set my GPS by the cache spot. Start it averaging. Place the cache, tweak the cammo job, then tell the GPS to save the reading.

Normally nobody complains about my coordinates. That's anywhere from 60 to 100 points averaged.

February 24, 2005

I would set my GPS out and take a 2-3 minute reading.

I know it sounds like a long time. But I usually don't have this problem because it takes me at least 2 minutes to dig a decent... hole... uh... I better go now.

3.1k · February 24, 2005

You can spend an hour averaging but if you have a lousy signal you'll be way off.

It's about a strong signal, if there isn't one, I don't hide there.

1.5k · February 24, 2005

I make sure to slow down to at least 25mph before tossing my caches out the window. I have my GPS ready to mark the waypoint, and press the button at the same time as I toss.

February 24, 2005

What is EPE? I'm guessing it is a metric of how much error is in the reading. My GPSr sometimes tells me an EPE reading and sometimes tells me how much time it has spent WAAS averaging. Which is better, an EPE reading or averaging?

For my placements I've let it average for 1 to 2 minutes before hitting the mark button.

February 24, 2005

I like very accurate coordinates and would use a surveyor's GPS if I could. Lacking that, I will do WAAS averaging if the signals are good. If I'm in leaf cover, I will average as best reasonable and then measure the distance from the cache to a clearing where I do get a better signal. I will then compare that reading from a few angles until I'm satisfied. But even then, I can come back later and ground zero is 20 feet off. <_<

24.7k · February 24, 2005

What is EPE? I'm guessing it is a metric of how much error is in the reading. My GPSr sometimes tells me an EPE reading and sometimes tells me how much time it has spent WAAS averaging. Which is better, an EPE reading or averaging?

For my placements I've let it average for 1 to 2 minutes before hitting the mark button.

Estimated Position Error. Your GPSs estimate of how much error there is in it's position calcuation. Of course the EPE also has error but we don't yet have EPEE

1.4k · February 24, 2005

EPE works basically like this. There is a 50% chance of the target being within your reported epe. If you double the distance, there is a 95% chance your target is within that area. ie:

Your gps says 1 foot from target, and your EPE is 20 feet.

Theres a 50% chance your target is in a 20 foot radius of your position, and a 95% chance it's within a 40 foot radius.

The better your signal and the longer you let WAAS averaging work, the lower your EPE will be.

3.3k · February 24, 2005

Here is how I take readings for my new caches. To date, no one has ever complained of "bad coords."

1. pick an area to hide a cache that has a clear sky for maximum satellite reception.

2. Follow you manufacturers suggestion on what is the best to position to hold your GPS for optimum signal reception. For Magellan Meridians, like mine, Thales recommends holding your GPS perpendicular to the ground.

3. If I want to hide my cache under heavy cover, I often use tree branches directly above the cache hiding spot, so as to get the best signal. I also try to keep my gps as close to vertical as possible.

4. I let my GPS sit motionless for 2 to five minutes, and let it average.

5. Post the coordinates on the new cache page, and enjoy the logs of happy cachers.

5.3k · February 24, 2005

Cachers who care about providing good coordinates tend to average them and take them quite carefully. Those who don't tend to try to justify themselves by claiming it makes no difference.

They are wrong. I can very clearly tell the difference between the accuracy of coordinates of experienced hiders compared to first-time hiders. Experimental evidence backs this up.

1.1k · February 24, 2005

I take three reading with each reading averaged 30 times, a stastically sighnifinte number. The only time I got bad readings this way was when I set the GPSr on a phone junction box, no the cache was NOT in or on the box, so there was some EMF interferance.

The main thing with GPSr accuracy is a myriad of problem ranging from satellite configuration to propgation of error. Thought I do not know how someone can get an error of 150feet unless they have the wrong datum.

cheers

February 24, 2005

For me in part it depends on location. How important are accurate coordinates in that location? How many good hiding places are within you circle of error. If its a lot, you owe it to the searcher to spend some time on it (normally I set down the GPS, and tell it to average out the coordinates for a minute or two).

I think we owe it to our cache followers to give them accurate coordinates no matter where the cache is. Unless of course you are "driving by and throwing it out the window". I liked that one I am placing a multi this week. One of the waypoints is a power pole in the middle of a park....nothing else around. I still took 5-10 minutes to walk off in several different directions to get an accurate reading even though there is nothing else around. Why? To make sure the hunt is fun and exciting not hair pulling-out aggrevating because they have to look 30 minutes for a WP.

There is another thread started this morning dealing with "quality" of caches. I think spending time on every cache making sure our coordinates are as accurate as possible adds to a quality cache. You might put out the best cache of the year but what good is it if the cachers can't find it or have to spend hours looking for it? I went out last night to take some final WP readings for the cache I am hiding this weekend. I took your suggestions and let my GPSr average for two minutes. I then walked off and did a goto back to the WP. The GPSr zeroed out 15' away from the WP. To me that is not acceptable. I spent 15 more minutes tweeking the coords until they were right on.

Just my 2c worth.

Red Bear

February 24, 2005

I let my Magellen average for at least 1 minute. If I've got a low EPE, usually 10-14', I let the coordinates stand. If I can't get a low EPE, I post a note on the page saying what the EPE was when I averaged.

I don't take multiple coordinatess and average them because when someone is hunting the cache, they simply walk to ground zero and search. They don't go in and out several times to try to average their coordinates. Besides, how much more accuracy do you get by averaging several readings? 6-12'?

Another 2c worth.

JetSkier

February 24, 2005

Estimated Position Error. Your GPSs estimate of how much error there is in it's position calcuation. Of course the EPE also has error but we don't yet have EPEE

I have epee. Wanna fence?

38.2k · February 24, 2005

Cachers who care about providing good coordinates tend to average them and take them quite carefully. Those who don't tend to try to justify themselves by claiming it makes no difference.

That is absolutely untrue. I care about providing good coordinates and I do. Look at my cache logs and you will rarely see a complaint about my coordinates. In fact you'll see frequent comments praising them.

I say it makes no difference because it doesn't. You can spend an hour averaging and I can take one reading. In some cases its actually possible that your averaging made your coords worse. Even if they are better than mine, they are better by what? 3 feet? 5 feet? I don't think that the additional effort required is worth the minute improvement you (may) get from averaging.

Edited February 25, 2005 by briansnat

February 24, 2005

i'm still waiting for the bisons for my first GC multi, but for my Terracaches i've placed, i've used WAAS averaging anywhere from 3-5 minutes, and gone back and checked. in the areas where i've maintained a WAAS signal for the period of averaging, there's usually no difference in coords. if there's no lock, i'll let my gpsr sit for a couple of minutes, mark it, then go back and do that a couple of times.

average them out when i get home, and it seems to be working.

in areas of really bad coverage (canyon, etc) i just make sure to note it, and give a better clue to compensate.

if i'm going to put out a cache, i'd like it to be found...

February 24, 2005

Look at my cache logs and you will rarely see a complaint about my coordinates. In fact you'll see frequent comments like "Brians coords were good as us

How many of us always post the comment "I had a terrible time finding the cache with the posted coords"? I don't always do it. I figure 1) they didn't take the time to get a good fix (thus the reason for this thread). 2) I'm not getting good coverage due to whatever reason. 3) the cache is there but I'm just not finding it. I found two caches last week that my GPS was pointing 50' in another direction. I found them because I have a few finds under my belt and I "knew" where to look. I didn't post any comment in reference to the 50' off because I didn't know why my GPS was 50' off (see #1 & #2 above).

38.2k · February 24, 2005

How many of us always post the comment "I had a terrible time finding the cache with the posted coords"?

I always do. I think the owner deserves to know his coords may be off. Judging from logs I've seen, including some for my caches, most people will mention coords that are bad. I never said there were no logs critical of my coords, but they are in the overwhelming minority.

February 25, 2005

Estimated Position Error. Your GPSs estimate of how much error there is in it's position calcuation. Of course the EPE also has error but we don't yet have EPEE

My Magellen Sportrak will tell me EPE or it will tell that it is WAAS or it will tell me that is is averaging WAAS, but it will only tell me one of them.

It seems to me that there is always an EPE, but I just can see it then.

Does this make sense? (I'm not home now so I can't read the manual)

Thanks!

Paul

1.8k · February 25, 2005

I get much better averaged coordinates with a GPS that will do the averaging for me. Usually I let my 60CS sit until it does a couple hundred readings, which takes a little more than a few minutes. Then I walk maybe 100 feet away and re-approach the area to make sure I zero at the same spot. I never trust a single reading from my GPS...but I'm just a techophobe like that.

1.4k · February 25, 2005

Estimated Position Error. Your GPSs estimate of how much error there is in it's position calcuation. Of course the EPE also has error but we don't yet have EPEE

My Magellen Sportrak will tell me EPE or it will tell that it is WAAS or it will tell me that is is averaging WAAS, but it will only tell me one of them.

It seems to me that there is always an EPE, but I just can see it then.

Does this make sense? (I'm not home now so I can't read the manual)

Thanks!

Paul

You can customize your sportraks screen to show both epe and waas averaging time.

February 25, 2005

so, when you look for a cache do you stand in one position for 20 min or so to let your gpsr settle in before looking, or do you look right away?

February 25, 2005

Estimated Position Error. Your GPSs estimate of how much error there is in it's position calcuation. Of course the EPE also has error but we don't yet have EPEE

I have epee. Wanna fence?

Now there is a novel idea. Never saw a cache placed with a fence around it. Should the cache be placed in the middle of the fenced area I wonder.

February 25, 2005

I haven't done any research of this theory, but I've noticed it on a few occasions ... the GPS satellites are in the same position in the sky every 12 hours, therefore, if you take a reading at 1pm, the reading seems to be more accurate at 1pm or 1am each day. If you compare them to readings at the same location at 7pm or 7am, you'll see an error of up to 50-60'. That's the nature of the beast. As I said, I haven't done any scientific research on this theory, but it sounds logical to me.

JetSkier

February 25, 2005

One figure you should keep an eye on is DOP (Dilution Of Precision). This figure should be as close to 1.0 as possible when you take your "final" reading. You really want to have a couple of minutes during which the DOP was never more than 1.5 when you punch-in your accepted coordinate.

If someone then says that "your coordinates are off," you should promptly return to the cache-site and re-check them. (Mistakes do happen, no matter how hard you try.) I think that it's very important that, following any NF's that say such things, you should be on-your-toes and post a followup note ... confirming that the problem was corrected, or that the cache is "pure evil" ... ... But responding, and in a timely manner, nonetheless.

February 26, 2005

I'll let my GPSr settle in the same spot for a few minutes and then let it start averaging. The spot chosen is sometimes more important than the time spent settling/averaging. For example if the cache location is under heavy cover I'll attempt to find a less obstructed location nearby with hopefully better accuracy and adjust the coordinates accordingly after the fact based on an estimated bearing and range to the cache. Obviously this isn't possible in all situations and any sizable offsets will require more work.

I rarely rely on a single data point either since I'll usually scope out the cache location in advance and take my readings then. Upon returning to place the prepared cache at a later time/date, I follow the arrow to the marked position and make sure it puts me in the ballpark - I'm trying to see the cache through the eyes of a finder. If I get to within 25ft or so I let the original coords stand, if not I'll repeat the process above and take an average of the two.

February 26, 2005

so, when you look for a cache do you stand in one position for 20 min or so to let your gpsr settle in before looking, or do you look right away?

If I am having a hard time finding a cache then I will let my GPSr settle while I look for it. Most of the time once I get to the area 10-15meters off I start looking for locations that I would Hide a cache in. Most of my 100+ finds are from using common sense once I got close.

I havn't hid many, but unless there is a obvious spot(ie. one tree in the middle of an open field) I will average a settled reading of 2-3 minutes taken at diffrent times of the day, or on diffrent days. Again this is if my Cache is under tree cover.

6.7k · February 26, 2005

What most everyone else said...

Plus, many of us (AGA members) ask a friend with a GPS to go on the hide. I carry 2 GPSrs when making a placement - a Magellan Meridian and a Magellan Meridian Platinum. My friends carry a mix of brands and models, mostly Garmin.

We spend 20 minutes or so (most folks don't realize how long 20 minutes really is - like logs that say "looked for an hour", I expect that if they really timed it would be 20 minutes!) collecting and if necessary averaging our coords to give the finder the most accurate coords possible.

That's a lot of work, and a lot of folks will think it's too much, but bad coords are our pet peeve! I never want to be responsible for a DNF or a new cacher losing interest because I was sloppy with my coords.

February 26, 2005

I'll take a couple of minutes. Personally I don't really want the coordinates to be absolutely perfect. I think the gps is just supposed to get you into a certain radius where you must then rely upon your instincts [sp?] to find the cache. More fun that way.

February 28, 2005

That's a lot of work, and a lot of folks will think it's too much, but bad coords are our pet peeve! I never want to be responsible for a DNF or a new cacher losing interest because I was sloppy with my coords.

I like this line of thinking...mainly because it is how I feel and why I started this thread. On the other hand...

Personally I don't really want the coordinates to be absolutely perfect. I think the gps is just supposed to get you into a certain radius where you must then rely upon your instincts [sp?] to find the cache. More fun that way.

brings about poor quality caches and aggravated cachers.

38.2k · February 28, 2005

Personally I don't really want the coordinates to be absolutely perfect. I think the gps is just supposed to get you into a certain radius where you must then rely upon your instincts [sp?] to find the cache. More fun that way.

brings about poor quality caches and aggravated cachers.

Its virtually impossible to get perfect coordinates and even if by chance you do, the searcher's GPS will have an error built in. So I don't see the point of spending a ton of time in hopes of adding an additional few feet of accuracy.

You can get perfectly fine coordinates with a good sat lock and one reading. If people choose to waste their time trying to perfect their coordinates, more power to them. I'll put the accuracy of my coords up against theirs anytime and while they're wasting their time fussing over their coordinates, I'll be out hunting or placing new caches.

Edited February 28, 2005 by briansnat

February 28, 2005

Personally I don't really want the coordinates to be absolutely perfect. I think the gps is just supposed to get you into a certain radius where you must then rely upon your instincts [sp?] to find the cache. More fun that way.

brings about poor quality caches and aggravated cachers.

Its virtually impossible to get perfect coordinates and even if by chance you do, the searcher's GPS will have an error built in. So I don't see the point of spending a ton of time in hopes of adding an additional few feet of accuracy.

You can get perfectly fine coordinates with a good sat lock and one reading. If people choose to waste their time trying to perfect their coordinates, more power to them. I'll put the accuracy of my coords up against theirs anytime and while they're wasting their time fussing over their coordinates, I'll be out hunting or placing new caches.

Good point Brian. Unless we are using the same piece of equipment, the exact same way, under the same exact conditions, there is going to be some variation in coordinates. If I use a hyper-accurate GPSR, and you use an old 8-sat unit is going to result in a difference in coordinates. Is that variation due to my GPSR, yours, or a combination of the two?

Tracy and I usually do not spend a lot of time waiting for coordinates to settle, we provide good coordinates, have never had a complaint about our coordinates, and care about providing fairly accurate coordinates. (So your comments above are greatly appreciated.)

March 23, 2005

I heard about Markwells and thought I'd look for answers to my big question about our first find and how to get accurate coordinates. This board has surpassed what I was hoping to find out about those tricky coords. My wife and I live on about a half acre, so I went out yesterday in overcast conditions and did a practice placement before we hide our first cache. I hid the cache and I averaged, holding the GPSr perpendicular and up. I only averaged for about a minute. When she went out to find it, we both found the coordinates to be between 15'-30' off. Boy that was a rude awakening. We're kinda thankful we didn't place that first cache yet. We want our coordinates to be as accurate as possible, so we will definitely be using some of the methods we read about here. We'll take satellite reception into account (cloudy day = bad reception), average for a longer time coming from different directions, etc. We know how frustrating it can be to get to the coords listed and then to find the cache 50 feet away from where they are posted. Then again, that's only happened a couple times in the few finds we've had. Thanks for all the great advice.

Ensuring Accurate Cache Coordinates

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