Placing caches with Just Google Earth and compass

[SF and JB]

I've been geocaching for less then a month and have found quite a few of them using just maps, Google Earth and a compass (I don't own a GPSr and am not planning to buy one) and today I came across one that was about 16 meters off of its posted coordinates.

 

I determined this using the Google Earth ruler tool and a bearing shot from a landmark only 25 meters from the cache with my compass while at GZ and it got me thinking that I could definitely place caches to within ~1 meter accuracy with just Google Earth and a compass, provided there were some landmarks visible from Google Earth near the cache site. I'm hoping I could peoples input on this method!

[ChefHazmat]

This is exactly what I'm using right now since I can't afford a GPS at the moment. I just print out the aerial view of the site and take that with me.

[jholly]

I've been geocaching for less then a month and have found quite a few of them using just maps, Google Earth and a compass (I don't own a GPSr and am not planning to buy one) and today I came across one that was about 16 meters off of its posted coordinates.

 

I determined this using the Google Earth ruler tool and a bearing shot from a landmark only 25 meters from the cache with my compass while at GZ and it got me thinking that I could definitely place caches to within ~1 meter accuracy with just Google Earth and a compass, provided there were some landmarks visible from Google Earth near the cache site. I'm hoping I could peoples input on this method!

 

First off the guidelines require the use of a GPS

You as the owner of the cache must visit the site and obtain the coordinates with a GPS. GPS usage is an essential element of geocaching. Therefore, although it is possible to find a cache without a GPS, the option of using accurate GPS coordinates as an integral part of the cache hunt must be demonstrated for all physical cache submissions.

 

Secondly the maps from Google may or may not be correctly aligned. Your estimated position might be off by quite a bit.

[knowschad]

In case it is necessary, I will second what JHolly said. You don't need a GPS to find a cache, but it required to hide one, and for good reason.

[+NeecesandNephews]

I can't recommend placing one without a GPSr. If all else fails, check the logs of one you have found recently, and get the name of another cacher who might be willing to beta test your coordinates for you. Shoot them a PM and ask if they would help you out.

 

Good way to make a caching friend at the same time. I would borrow one if that failed. I wouldn't trust the listings that had not at least been confirmed by one.

[+edscott]

Gotta use a GPS to hide caches. These old timers expect a 20 ft search radius so a perfect placement messes with their minds.

[+t4e]

went hunting for one that later turned out to have been hidden just using google maps, don't want to encounter another one ever, its not fun searching for something that points you in the middle of a 4 lane street

it was archived 2 days later

[+edscott]

went hunting for one that later turned out to have been hidden just using google maps, don't want to encounter another one ever, its not fun searching for something that points you in the middle of a 4 lane street

it was archived 2 days later

 

Sounds like they used the "map" view not the satellite image.

[SF and JB]

I should add a link to the specific cache I'm talking about:

 

http://www.geocaching.com/seek/cache_detai...93-7509bb676c51

 

My log entry was from today and is below:

 

"N 45° 24.446 W 075° 40.333

 

Found it after some searching, I only used map and compass and shot a bearing from the N pointing corner of the tennis court. The cache coordinates are about 16m NW of the cache itself, I shot a bearing from the same corner of the tennis court before leaving and used it and google earth to determine approximately where the cache is and have posted those coordinates with this post. The cache was in pretty plain view as well, but I covered it up a bit more, TNLNSL. TFTC!"

 

Someone also alluded to problems with Google Earth not being properly geo referenced, does anyone have examples of this? I know that imagery age can certainly be a problem, but I haven't been in a situation yet where I've felt the geo referencing was actually off.

[+narcissa]

Repeating what others have said - if you want to FIND a cache with Google Earth, whatever. But don't HIDE a cache with Google Earth unless you want a lot of angry NA logs. Google Earth is awesome, but the accuracy of its coordinates is too inconsistent for cache placement.

[SF and JB]

I can't recommend placing one without a GPSr. If all else fails, check the logs of one you have found recently, and get the name of another cacher who might be willing to beta test your coordinates for you. Shoot them a PM and ask if they would help you out.

 

Good way to make a caching friend at the same time. I would borrow one if that failed. I wouldn't trust the listings that had not at least been confirmed by one.

 

That sounds like a good work around, thanks! I do think its possible to accurately place caches in some areas with just map and Google Earth. That is unless there are problems with Google Earth's geo referencing.

[SF and JB]

Also, what are peoples' thoughts on letterboxes, it'd probably be alright to place general coordinates that are near a letterbox with just a compass and GPS, right? Here's an example of what I'm envisioning:

 

http://www.geocaching.com/seek/cache_detai...4b-fa4f5e5dbe3f

[SF and JB]

I can't recommend placing one without a GPSr. If all else fails, check the logs of one you have found recently, and get the name of another cacher who might be willing to beta test your coordinates for you. Shoot them a PM and ask if they would help you out.

 

Good way to make a caching friend at the same time. I would borrow one if that failed. I wouldn't trust the listings that had not at least been confirmed by one.

 

That sounds like a good work around, thanks! I do think its possible to accurately place caches in some areas with just map and Google Earth. That is unless there are problems with Google Earth's geo referencing.

 

I'll add a caveat to that, which is I understand that rules are rules and are there for what I imagine are pretty good reasons.

[SF and JB]

went hunting for one that later turned out to have been hidden just using google maps, don't want to encounter another one ever, its not fun searching for something that points you in the middle of a 4 lane street

it was archived 2 days later

 

Do you have a link to it? Just to satisfy my own curiosity is all.

[+narcissa]

Also, what are peoples' thoughts on letterboxes, it'd probably be alright to place general coordinates that are near a letterbox with just a compass and GPS, right? Here's an example of what I'm envisioning:

 

http://www.geocaching.com/seek/cache_detai...4b-fa4f5e5dbe3f

 

"Letterbox hybrids are a mixture of letterbox and geocache. They should contain a signature stamp that stays with the box, and they must conform to the guidelines for geocaches and therefore must contain a logbook and involve GPS use as an integral part of the hunt. A letterbox hybrid cannot be designed to be found using only clues."

 

http://www.geocaching.com/about/guidelines.aspx#letterbox

 

I'm not trying to be mean, but I think you should stop looking for ways to circumvent the guidelines and wait until you have a GPS before you start hiding caches.

 

Or take up actual letterboxing.

[knowschad]

Gotta use a GPS to hide caches. These old timers expect a 20 ft search radius so a perfect placement messes with their minds.

Irrelevant what "these old timers" want, aside from the "old timers" that run this place. Them's their rules, not ours.

[+StarBrand]

The published accuracy of most maps is gno better than 48 feet at well known locations.

 

Google Earth imagery is known to be way off in some areas and spot on in others. Trouble is - you just can't trust it. Several areas west of Scottsbluff Nebraska are about 100 foot off.

 

I'll trust my GPS - thanks.

[SF and JB]

Also, what are peoples' thoughts on letterboxes, it'd probably be alright to place general coordinates that are near a letterbox with just a compass and GPS, right? Here's an example of what I'm envisioning:

 

http://www.geocaching.com/seek/cache_detai...4b-fa4f5e5dbe3f

 

"Letterbox hybrids are a mixture of letterbox and geocache. They should contain a signature stamp that stays with the box, and they must conform to the guidelines for geocaches and therefore must contain a logbook and involve GPS use as an integral part of the hunt. A letterbox hybrid cannot be designed to be found using only clues."

 

http://www.geocaching.com/about/guidelines.aspx#letterbox

 

I'm not trying to be mean, but I think you should stop looking for ways to circumvent the guidelines and wait until you have a GPS before you start hiding caches.

 

Or take up actual letterboxing.

 

So I guess that one kind of breaks the rules then? There wasn't a stamp or anything in it, it was just a geocache, the only difference was that the posted coordinates were intentionally off, but close to the cache.

[+narcissa]

Also, what are peoples' thoughts on letterboxes, it'd probably be alright to place general coordinates that are near a letterbox with just a compass and GPS, right? Here's an example of what I'm envisioning:

 

http://www.geocaching.com/seek/cache_detai...4b-fa4f5e5dbe3f

 

"Letterbox hybrids are a mixture of letterbox and geocache. They should contain a signature stamp that stays with the box, and they must conform to the guidelines for geocaches and therefore must contain a logbook and involve GPS use as an integral part of the hunt. A letterbox hybrid cannot be designed to be found using only clues."

 

http://www.geocaching.com/about/guidelines.aspx#letterbox

 

I'm not trying to be mean, but I think you should stop looking for ways to circumvent the guidelines and wait until you have a GPS before you start hiding caches.

 

Or take up actual letterboxing.

 

So I guess that one kind of breaks the rules then? There wasn't a stamp or anything in it, it was just a geocache, the only difference was that the posted coordinates were intentionally off, but close to the cache.

 

If there's no stamp, it doesn't meet the requirement for a letterbox hybrid. Unfortunately, some people are dumb and take the stamps as swag, so it may not be the cache owner's fault.

[+narcissa]

Haha, my bf and I were part of the crowd that were FTF on that cache. I'm pretty certain there was a stamp in it to begin with - my boyfriend is very particular about Letterbox caches and would have said something to Mr. Packrat if there wasn't a stamp.

[+t4e]

went hunting for one that later turned out to have been hidden just using google maps, don't want to encounter another one ever, its not fun searching for something that points you in the middle of a 4 lane street

it was archived 2 days later

 

Sounds like they used the "map" view not the satellite image.

 

the "map" view won't give you coordinates, satellite view does

[+t4e]

went hunting for one that later turned out to have been hidden just using google maps, don't want to encounter another one ever, its not fun searching for something that points you in the middle of a 4 lane street

it was archived 2 days later

 

Do you have a link to it? Just to satisfy my own curiosity is all.

 

sorry i should have said "retracted" by the reviewer

 

there was a group of 7 of us that went to GZ 2 days in a row, with no luck, than after many notes, the owner replied that he has no GPS and used google and said he will get a neighbor with a GPS to fix it so he returned and posted a note that is all good to go, only to admit, after 2nd round of notes we all posted, that turned out the neighbor couldn't help him so he only moved it in a better spot with the help of the satellite readings

 

at this point the reviewer jumped in and "retracted' the listing...the cache was called "westmount cache", its been used as a running joke since than, for caches with really bad coordinates

[+narcissa]

Have you checked out the Ottawa geocaching community at all? We have a monthly workshop at the Dovercourt community centre, and a monthly "meet and eat" at Summerhay's restaurant.

 

Check out our forum:

 

http://www.ottawageocaching.com/forum

 

I have two spare GPSrs I'm not using and I would be happy to lend one of them to you to help you get started.

[+NeecesandNephews]

I don't think anyone responding here is trying to discredit your methods accuracy in an insulting way. I mean they used to use surveying chains!

 

Even if your methods and skilled application of them are sound, unless the hunter is using the same methods with the same skill level, the results are going to be dissappointing.

 

The accuracy of GPS is a much debated topic in this forum. Nevertheless...

 

Trust me when I tell you, while I have seen several instances of intentionaly wrong or innacurate coordinates posted by Cache hiders who thought it was funny, I have yet to run into one on here, or out in the world , who shared that amusement.

 

You would be doing yourself a favor, and saving yourself a world of grief, if you would just use a GPS. After all... it is the basis of the Website and the game that is played here.

 

edit to add- just caught Narcissa's last post. It just doesn't get any easier than that!!

Edited March 13, 2010 by NeecesandNephews

[jholly]

Also, what are peoples' thoughts on letterboxes, it'd probably be alright to place general coordinates that are near a letterbox with just a compass and GPS, right? Here's an example of what I'm envisioning:

 

http://www.geocaching.com/seek/cache_detai...4b-fa4f5e5dbe3f

 

Letterboxes don't use co-ordinates, they use directions. Letterboxing was started long before GPS satellites were even dreamed up.

[+narcissa]

Also, what are peoples' thoughts on letterboxes, it'd probably be alright to place general coordinates that are near a letterbox with just a compass and GPS, right? Here's an example of what I'm envisioning:

 

http://www.geocaching.com/seek/cache_detai...4b-fa4f5e5dbe3f

 

Letterboxes don't use co-ordinates, they use directions. Letterboxing was started long before GPS satellites were even dreamed up.

 

I think the OP was referring to Letterbox Hybrid geocaches, since that's what the link was for.

[+Taoiseach]

Have you checked out the Ottawa geocaching community at all? We have a monthly workshop at the Dovercourt community centre, and a monthly "meet and eat" at Summerhay's restaurant.

 

Check out our forum:

 

http://www.ottawageocaching.com/forum

 

I have two spare GPSrs I'm not using and I would be happy to lend one of them to you to help you get started.

 

I'll add to this that if you'd like to learn what a Letterbox Hybrid is, I'd be happy to go and take you through 'Welcome to Ottawa'

 

Or 'An Ode to Brian'

[+dfx]

now if you'd take actual geo survey marks, benchmarks etc as reference points and triangulate properly, you may actually have a good chance of getting proper coordinates. however it's still against the rules, and if you screw up and people find out you didn't use a GPS, they're gonna be very angry.

[+narcissa]

 

I'll add to this that if you'd like to learn what a Letterbox Hybrid is, I'd be happy to go and take you through 'Welcome to Ottawa'

 

Or 'An Ode to Brian'

 

 

[+Taoiseach]

 

I'll add to this that if you'd like to learn what a Letterbox Hybrid is, I'd be happy to go and take you through 'Welcome to Ottawa'

 

Or 'An Ode to Brian'

 

 

 

[+tozainamboku]

Gotta use a GPS to hide caches. These old timers expect a 20 ft search radius so a perfect placement messes with their minds.

Irrelevant what "these old timers" want, aside from the "old timers" that run this place. Them's their rules, not ours.

My guess is that many caches are hidden using coordinates from Google maps and that so long as nobody mentions it, the coordinates are just as good as any with a GPS. But if you tell people that you didn't use a GPS, you'll find some geocacher who will insist that your coordinates are way off and will post the the "corrected GPS coordinates". Of course, that makes the OP's log funny. He claims that coordinates are off and lists the ones he got on Google Maps. However since the cache owner corrected the coordinates in October 2006 no one else had posted corrected coordinates till today. I'd probably trust the GPS coordinates in this case.

[+NeecesandNephews]

Ok, after Toz' post I went back and searched the cache you quoted above. I did not realize the coordinates you posted in your quoted log were not the cache listing coordinates.

 

Someone also alluded to problems with Google Earth not being properly geo referenced, does anyone have examples of this?

 

I do.... here's one example:

 

"N 45° 24.446 W 075° 40.333

 

Found it after some searching, I only used map and compass and shot a bearing from the N pointing corner of the tennis court. The cache coordinates are about 16m NW of the cache itself, I shot a bearing from the same corner of the tennis court before leaving and used it and google earth to determine approximately where the cache is and have posted those coordinates with this post. The cache was in pretty plain view as well, but I covered it up a bit more, TNLNSL. TFTC!"

 

 

I did not realize you found the innacuracy of the coordinates of this cache to be due to GPS and not perhaps your methods.

 

 

Thanks Toz!

[+dfx]

My guess is that many caches are hidden using coordinates from Google maps and that so long as nobody mentions it, the coordinates are just as good as any with a GPS.

somehow i doubt it. do you have any estimate on how far "off" you find the caches to be from where they should be according to your system?

[+edscott]

Gotta use a GPS to hide caches. These old timers expect a 20 ft search radius so a perfect placement messes with their minds.

Irrelevant what "these old timers" want, aside from the "old timers" that run this place. Them's their rules, not ours.

 

...and I suspect those rules are there because when GPS coordinates are used it doesn't matter how much brain power is attached to the other end, but when using the satellite image one must interpret the data correctly.

[+narcissa]

Ok, after Toz' post I went back and searched the cache you quoted above. I did not realize the coordinates you posted in your quoted log were not the cache listing coordinates.

 

Someone also alluded to problems with Google Earth not being properly geo referenced, does anyone have examples of this?

 

I do.... here's one example:

 

"N 45° 24.446 W 075° 40.333

 

Found it after some searching, I only used map and compass and shot a bearing from the N pointing corner of the tennis court. The cache coordinates are about 16m NW of the cache itself, I shot a bearing from the same corner of the tennis court before leaving and used it and google earth to determine approximately where the cache is and have posted those coordinates with this post. The cache was in pretty plain view as well, but I covered it up a bit more, TNLNSL. TFTC!"

 

 

I did not realize you found the innacuracy of the coordinates of this cache to be due to GPS and not perhaps your methods.

 

 

Thanks Toz!

 

Haha, just went and looked at that. Model12 uses a Map60 and has over 6000 finds... if he reads that log, he'll get a good laugh at seeing his coordinates "corrected" with Google Earth.

[+Setan Meyacha]

I pick a lot of my cache hiding places using GoogleEarth; but, only as a general location until I actually get to the spot to find out whether it is worth placing a cache in that location. Then, after I've found a hiding spot, I use my GPSr to take a number of readings to be as accurate as I can be in the coordinates posted. Sometimes rock walls, water, trees or other factors can still put those coordinates off by as much as forty feet, in one instance. When that happens, as usually the FTF will let me know, I go back out and see if I can find the same location using my original coordinates. If not, then I adjust the coordinates based on what the finder thought they should be and an average of the new coordinates I take at that time. I've only had one cache placed almost exactly in the spot I picked out on the map. I only use GoogleEarth as a means of finding likely hiding spots.

[SF and JB]

Ok, after Toz' post I went back and searched the cache you quoted above. I did not realize the coordinates you posted in your quoted log were not the cache listing coordinates.

 

Someone also alluded to problems with Google Earth not being properly geo referenced, does anyone have examples of this?

 

I do.... here's one example:

 

"N 45° 24.446 W 075° 40.333

 

Found it after some searching, I only used map and compass and shot a bearing from the N pointing corner of the tennis court. The cache coordinates are about 16m NW of the cache itself, I shot a bearing from the same corner of the tennis court before leaving and used it and google earth to determine approximately where the cache is and have posted those coordinates with this post. The cache was in pretty plain view as well, but I covered it up a bit more, TNLNSL. TFTC!"

 

 

I did not realize you found the innacuracy of the coordinates of this cache to be due to GPS and not perhaps your methods.

 

 

Thanks Toz!

 

In my defense, I was shooting bearings from a point that was only ~25 meters from the posted coordinates and the actual geo cache, so I think my methods were quite accurate. I believe the problem may be with Google Earth and how it's aerial and/or satellite imagery is geo referenced, in the end it'll probably require me to go back to the cache with a GPSr with an averaging function to determine what the actual problem is, Google Earth or the posted coordinates, which I might try at some point in the future. In the end I suppose I may have been a little quick to assume that my coordinates were the correct ones. Perhaps next time I post a correction I'll endeavor to be clearer by stating something like "Google Earth says that the cache should be here"

[SF and JB]

Have you checked out the Ottawa geocaching community at all? We have a monthly workshop at the Dovercourt community centre, and a monthly "meet and eat" at Summerhay's restaurant.

 

Check out our forum:

 

http://www.ottawageocaching.com/forum

 

I have two spare GPSrs I'm not using and I would be happy to lend one of them to you to help you get started.

 

That sounds awesome, I'll check out the forum, if I ever get really serious about placing a cache, maybe I'll take you up on that offer to borrow the GPSr. I was actually going to go to the workshop on Thursday, but I had class.

[+ghettomedic]

If you want a visual example of Google Earth being off, this is a screen capture of one of my hides. Off by 55 feet+/-

 

[+Lil Devil]

My log entry was from today and is below:

 

"N 45° 24.446 W 075° 40.333

 

Found it after some searching, I only used map and compass and shot a bearing from the N pointing corner of the tennis court. The cache coordinates are about 16m NW of the cache itself, I shot a bearing from the same corner of the tennis court before leaving and used it and google earth to determine approximately where the cache is and have posted those coordinates with this post. The cache was in pretty plain view as well, but I covered it up a bit more, TNLNSL. TFTC!"

Interesting. You claim the cache is 45 feet off, but only 1 other person out of 183 finds mentions anything about the coords being off, and that person found it shortly after the cache owner posted new coords, so he may have been using the old ones.

 

So why should I believe your map and ignore the 181 GPSes?

[7rxc]

Would be interesting to 'shoot' some easy to spot (from GE / GM) benchmarks for comparison... using both methods. I'm sure that the government would love to correct their placements.

 

Doug

[SF and JB]

If you want a visual example of Google Earth being off, this is a screen capture of one of my hides. Off by 55 feet+/-

 

 

I guess this points out some orthorectification/geo referencing problems with Google Earth. It'd be interesting to do a bit of an audit of Google Earth by finding really easily visible locations with clear views of the sky with no buildings for double readings to interfere with signal accuracy and operate a GPSr in averaging mode at those locations and then compare with where Google Earth says they should be.

[SF and JB]

My log entry was from today and is below:

 

"N 45° 24.446 W 075° 40.333

 

Found it after some searching, I only used map and compass and shot a bearing from the N pointing corner of the tennis court. The cache coordinates are about 16m NW of the cache itself, I shot a bearing from the same corner of the tennis court before leaving and used it and google earth to determine approximately where the cache is and have posted those coordinates with this post. The cache was in pretty plain view as well, but I covered it up a bit more, TNLNSL. TFTC!"

Interesting. You claim the cache is 45 feet off, but only 1 other person out of 183 finds mentions anything about the coords being off, and that person found it shortly after the cache owner posted new coords, so he may have been using the old ones.

 

So why should I believe your map and ignore the 181 GPSes?

 

Good question! I've had quite a bit of success in the short time I've been Geo Caching with my methods and have found caches where where Google Earth says they are and where they actually are is down to at least sub meter accuracy. This one didn't correspond to where Google Earth said it was, so that leads me to believe that there's either a geo referencing/orthorectification problem with Google Earth in the vicinity of this cache or the coordinates are actually off. The cache is a pretty easy one to find even with the coords being a little off, so I can see why people may not be inclined to mention or really even notice.

 

I'm going to try to borrow a GPSr at some point and see what kind of results I get from a long period of time left in averaging mode on a nice clear day.

 

I'd also like to make it clear that I get that the burden of proof is definitely on me with respect to this claim.

[GOF and Bacall]

Just to toss on a bit more food for thought consider what GE and such maps are. Using a large number of 2d flat pictures to represent a 3d globe. There needs to be a certain amount fudge factor to make it work.

[SF and JB]

Just to toss on a bit more food for thought consider what GE and such maps are. Using a large number of 2d flat pictures to represent a 3d globe. There needs to be a certain amount fudge factor to make it work.

 

I think you're right, I don't believe that the orthorectification process is perfect and honestly as long as everything on the map is spaced accurate distances in relation to each other it's still a safe tool to use even if the grid coordinates don't overlay on top of it perfectly. As mentioned previously I'm going to endeavor to discover just how much this error really is.

[+narcissa]

Just to toss on a bit more food for thought consider what GE and such maps are. Using a large number of 2d flat pictures to represent a 3d globe. There needs to be a certain amount fudge factor to make it work.

 

I think you're right, I don't believe that the orthorectification process is perfect and honestly as long as everything on the map is spaced accurate distances in relation to each other it's still a safe tool to use even if the grid coordinates don't overlay on top of it perfectly. As mentioned previously I'm going to endeavor to discover just how much this error really is.

 

The Google Earth error varies from place to place.

 

I'm sure that for many traditional caches, Google Earth will get you close enough to find it. It might even be good enough, sometimes, to hide a cache.

 

But it might not be, and then you run the risk of annoying a lot of people, including the cache reviewers. Remember, when you publish a geocache, you have to click those two little boxes declaring that you've read, understood, and followed the guidelines.

 

Again, not trying to be mean, but it's a little presumptuous of you to tell a seasoned cacher with thousands of geocache finds and hundreds of hides that his coordinates are wrong based on Google Earth and a compass. It's neat that you're doing it this way, but Google Earth's inaccuracy is well known and much discussed in the caching community. A Garmin Map 60CX calculating coordinates on the spot with signals from 10 satellites vs. Google Earth and a compass in a region with a variable magnetic declination? I'll place my bets on the GPS.

[SF and JB]

I think you're right, I don't believe that the orthorectification process is perfect and honestly as long as everything on the map is spaced accurate distances in relation to each other it's still a safe tool to use even if the grid coordinates don't overlay on top of it perfectly. As mentioned previously I'm going to endeavor to discover just how much this error really is.

 

The Google Earth error varies from place to place.

 

I'm sure that for many traditional caches, Google Earth will get you close enough to find it. It might even be good enough, sometimes, to hide a cache.

 

But it might not be, and then you run the risk of annoying a lot of people, including the cache reviewers. Remember, when you publish a geocache, you have to click those two little boxes declaring that you've read, understood, and followed the guidelines.

 

Again, not trying to be mean, but it's a little presumptuous of you to tell a seasoned cacher with thousands of geocache finds and hundreds of hides that his coordinates are wrong based on Google Earth and a compass. It's neat that you're doing it this way, but Google Earth's inaccuracy is well known and much discussed in the caching community. A Garmin Map 60CX calculating coordinates on the spot with signals from 10 satellites vs. Google Earth and a compass in a region with a variable magnetic declination? I'll place my bets on the GPS.

 

When I said safe to use I should have specified that I meant generally safe for personal navigation, not for placing caches. For the most part I understand and accept the argument against placement with just the tools I use now. Still to satisfy my own curiosity I am still going to try to borrow a GPSr and do a confirmation of the cache and a wider confirmation of GE using recognizable landmarks, as like I said my methods have produced sub meter accuracy in the past and as well I'd like to get a better idea of the limits of the tools I use.

 

There was perhaps a slight degree of presumptuousness to my log on the subject cache, but I think in the future I'll still mention discrepancies between GE and cache coords as I think it might help prevent confusion from people who find caches as I do or even just for regular cachers who like to use GE before they get on site (not sure if this is overly common or not actually, but whatever). I will also change my wording a bit as well, rather then calling the posted coords off, I'll just mention that there's a discrepancy between the two, as that really is what is more likely to be the case.

[+narcissa]

Taoiseach and I had some time to kill this afternoon so we took a few waypoints at objects we'd be able to see on Google Earth. We used my Garmin Dakota 20, chose open spots (one park, two parking lots) and had good satellite reception.

 

I then plotted the coordinates on Google Earth, and plotted second markers on the actual object as seen in Google Earth. For the first object, there was a 30 metre difference between the GPS coordinates and Google Earth's coordinates. For the second object, there was almost no difference. For the third object, there was maybe a 5 metre difference.

 

If you do a Google search on this topic, there are all sorts of discussions about this. Many GPS owners have done little tests to compare their GPS coordinates with Google Earth. Sometimes, the difference is negligible, but it's not uncommon to see fairly large differences in the range of 20 to 100 metres.

 

There are many factors involved. First, there is always a margin of error of at least a few feet with any handheld GPS device. I generally won't even notice that a cache's coordinates are "off" unless they're off by 15 metres or more, and it would have to be more than that before I'd bother mentioning it to a cache owner.

 

The possibility for error is even greater on Google Earth's end, though. Sometimes there are small errors in the way the photos are aligned. Sometimes the angle at which the photograph was taken can skew distances. In many rural areas, the photographs are too low-resolution to allow for perfect positioning.

 

Google Earth is nifty and fun, and by all means, if it works for you, keep using it to FIND caches. But don't use it to hide caches, or to "correct" someone else's coordinates unless you're set on annoying/alienating other geocachers.

[+narcissa]

Sorry, wrote that post before I saw your reply.

[+sullude]

I've been geocaching for less then a month and have found quite a few of them using just maps, Google Earth and a compass (I don't own a GPSr and am not planning to buy one) and today I came across one that was about 16 meters off of its posted coordinates.

 

I determined this using the Google Earth ruler tool and a bearing shot from a landmark only 25 meters from the cache with my compass while at GZ and it got me thinking that I could definitely place caches to within ~1 meter accuracy with just Google Earth and a compass, provided there were some landmarks visible from Google Earth near the cache site. I'm hoping I could peoples input on this method!

 

First off the guidelines require the use of a GPS

You as the owner of the cache must visit the site and obtain the coordinates with a GPS. GPS usage is an essential element of geocaching. Therefore, although it is possible to find a cache without a GPS, the option of using accurate GPS coordinates as an integral part of the cache hunt must be demonstrated for all physical cache submissions.

 

Secondly the maps from Google may or may not be correctly aligned. Your estimated position might be off by quite a bit.

 

With some of these people out there I would love for someone to use goggle map off by 150 ft or even 60 because they don't take multi readings. Plus why do you need a GPS I known a couple of people that use only maps plus goggle is pretty dadgum close on the coords