Co-Ordinates Consistently Off?

[VE7RJT]

I'm hoping to get one kind of an answer to this question, but I've got a bad feeling I'm not going to get the answer that I want.

 

I placed a cache that was declined due to being too close to another cache. That's fine - I know the other cacher, and he submitted first. I don't have a problem with that. I placed the cache hidden inside a wood carving on a pedestal. His cache (part of a multi) takes the co-ordinates based on reading the plaque attached to the pedestal.

 

My readings: N 49.06.542 - W 122.38.959

His co-rods: N 49.06.545 - W 122.38.951

 

I should mention that when I took the readings for my cache, I placed the GPSr *on* the plaque that he got his same readings from. Yet the reviewer rejected the cache reporting that it was only 10m (37 feet) from the other cache. Unfortunately, I've found that on both of my hides, I've gotten reports that the co-ordinates are out. No matter how many times I get readings. Usually by about 10m or so. Evidently it's my GPSr (a Nextar X3-01).

 

Unfortunately, the X3-01 is not the sort of GPSr with the compass/arrow that points directly to the cache. I've got to check the GPS co-ordinates based on how it reports them (in decimal: 49.xxxxx - 122.xxxxx, etc) and then they get converted when I submit the cache for review. Unfortunately there isn't a way to automatically 'average' the co-ordinates that I get. Is there a way to do it manually?

 

My main question (finally) is this: seeing as how it seems to be consistently out by about 10m, is safe to assume that it's going to be out (roughly) the same amount each time and could I add 2-4 points to the north co-ord, and 7-9 on the west co-ord?

 

At this point in time, a new GPSr isn't an option, and I'd really hate to have this issue (which comes into play when finding caches, too) make me have to give up the hobby which I've come to enjoy so much.

 

As I mentioned above, I have a feeling that the answer is going to be "No, you can't assume that it's off the same amount each time," but I thought I'd check anyway.

 

Any advice that anyone could provide would be very greatly appreciated.

[Motorcycle_Mama]

I would say that your GPS unit seems to be reading typically for recreational GPS units. Modern recreational GPS units typically have an accuracy of 20-30 feet. Older units might have a slightly greater margin of error.

 

It's possible that your GPS unit will always be "off" in the same direction(s), but I wouldn't assume that that will always be the case. It's possible that depending upon the satellites that are locked, that the error might be in a different direction. So I wouldn't necessarily just "add to" the coordinates.

 

The biggest thing that stuck out to me in your post however, was the part where you indicated that you couldn't place your cache because it was within 37 feet of another cache. Caches must be at least 528 feet from other physical caches. So I'm not sure that this would be "corrected" by "more accurate" coordinates.

[VE7RJT]

I would say that your GPS unit seems to be reading typically for recreational GPS units. Modern recreational GPS units typically have an accuracy of 20-30 feet. Older units might have a slightly greater margin of error.

 

It's possible that your GPS unit will always be "off" in the same direction(s), but I wouldn't assume that that will always be the case. It's possible that depending upon the satellites that are locked, that the error might be in a different direction. So I wouldn't necessarily just "add to" the coordinates.

 

The biggest thing that stuck out to me in your post however, was the part where you indicated that you couldn't place your cache because it was within 37 feet of another cache. Caches must be at least 528 feet from other physical caches. So I'm not sure that this would be "corrected" by "more accurate" coordinates.

 

Yes, I'm aware that they can't be any closer than 528 feet. What struck me was that readings taken in the *exact* same location were so vastly different. And based on the fact that I've heard of my co-ords being out before, I'm confident in saying it's probably my GPS rather than the other person's that's got incorrect co-ordinates.

 

So should I just assume that if I hide, my co-ords are going to be out (that's not going to make me particularly popular), or mention in the listing that they could be anywhere in a 20-30' radius of the listed co-ordinates? Or should I just walk away from hiding caches until someday I get a better GPSr?

[+Gitchee-Gummee]

I am not familiar with your Nextar unit, but after reading the reviews of same, I think you already answered your own question.

 

If you do not have good luck in finding caches with it, do you think you are going to have any better "luck" in placing good caches with it?

 

I do not think that interpolating (by adding/subtracting "points") is a viable solution. That constitutes little more than a guessing game on your part, and you are subjecting cachers with more "accurate" GPSr units to guess upon your guesses (and they would probably have no idea that you were guessing!)

 

Kentucky windage is probably good for shooting, but I doubt that it has much use in cache placement.

 

In-car units are becoming better for geocaching though still not up to a par with dedicated hand-held units. That however, doesn't help you either as the ultimate solution still would require replacement of the unit you have.

 

Sorry , but I think the answer you don't want to hear is the answer you are going to get.

 

Perchance you can "team" up with another cacher, and borrow their unit for placements until such time that you can acquire a better unit. There are used units for sale a very reasonable prices. You don't need a brand new, top of the line, bells and whistles unit.

[+Minimike2]

Perhaps you have your GPSr set to a different datum?

[+jhauser42]

Unfortunately, the X3-01 is not the sort of GPSr with the compass/arrow that points directly to the cache. I've got to check the GPS co-ordinates based on how it reports them (in decimal: 49.xxxxx - 122.xxxxx, etc) and then they get converted when I submit the cache for review. Unfortunately there isn't a way to automatically 'average' the co-ordinates that I get. Is there a way to do it manually?

 

To take a manual average you are going to have to take several readings. Go the cache site, let your GPSr settle and then take the reading. Go to a point about 60 feet (20 meters) away in a different direction and then approach again. Let the GPSr settle and take the reading. Do this from 3-5 different directions, then take the average of the readings.

 

In your example you had N 49.06.542 - W 122.38.959. If your 3 readings turn out to be:

 

N 49.06.542 - W 122.38.959

N 49.06.539 - W 122.38.952

N 49.06.548 - W 122.38.951

 

use the average:

 

N 49.06.545 - W 122.38.954.

 

It may not be perfect, but it will help to alleviate some errors. You can also take the readings on several different days to help account for satellite patterns and weather conditions.

[VE7RJT]

 

I do not think that interpolating (by adding/subtracting "points") is a viable solution. That constitutes little more than a guessing game on your part, and you are subjecting cachers with more "accurate" GPSr units to guess upon your guesses (and they would probably have no idea that you were guessing!)

 

Agreed. Not something I was really considering. Just something I threw out there, though.

 

Sorry , but I think the answer you don't want to hear is the answer you are going to get.

 

Perchance you can "team" up with another cacher, and borrow their unit for placements until such time that you can acquire a better unit. There are used units for sale a very reasonable prices. You don't need a brand new, top of the line, bells and whistles unit.

 

Thanks for the information. I actually thought of getting someone to check the co-ordinates for me with a 'better' GPS than my own before publishing. Going to have to look up a local, I guess. And start looking at eBay for a different GPSr.

[VE7RJT]

Unfortunately, the X3-01 is not the sort of GPSr with the compass/arrow that points directly to the cache. I've got to check the GPS co-ordinates based on how it reports them (in decimal: 49.xxxxx - 122.xxxxx, etc) and then they get converted when I submit the cache for review. Unfortunately there isn't a way to automatically 'average' the co-ordinates that I get. Is there a way to do it manually?

.

.

.

 

It may not be perfect, but it will help to alleviate some errors. You can also take the readings on several different days to help account for satellite patterns and weather conditions.

 

Thanks very much. That's probably what I'm going to have to do. Just a little more work to make things a whole lot better. Appreciate the explanation.

[VE7RJT]

Perhaps you have your GPSr set to a different datum?

 

Not really a way to change the datum on this one. It's pretty limited. But to be safe, I have checked into that myself just to make sure that that wasn't the issue. Thanks for the suggestion, though.

[crawil]

Plugging each set of coordinates into Google Maps puts me in the road - each on a different one, too! I would "borrow" another cacher and the GPSr and see what coords you can get.

[+KeeperOfTheMist]

looks about right for most gpsr's though the difference in coords looks almost like your gps uses the old datum (nad) in decimal (i had a iden phone that used that) also if you find it is in old datum format then you will know how to get better accuracy when seeking caches as well, them .003 can be a pain and maybe even put you on the wrong side of the creek in some places if your thinking its using wgs and its nad

[+niraD]

What struck me was that readings taken in the *exact* same location were so vastly different.

Consumer GPS receivers are accurate to about 3m (10') under ideal circumstances. Under less than ideal circumstances, it's easy for that distance to double or triple.

 

This applies to both your GPS receivers. So one receiver could be off by 20-30' in one direction, and the other receiver could be off by 20-30' in another direction. Rounding errors from format conversions can add another 1-2m (3-6').

 

Others have offered suggestions for averaging readings taken at different times, on different days. That can help improve the accuracy of your readings.

 

When I confirm my cache coordinates, I approach the cache from several directions, and verify that the arrow points to the cache regardless of the direction I approach it from. I'm not sure how to do that with a GPSr that doesn't have an arrow.

[VE7RJT]

looks about right for most gpsr's though the difference in coords looks almost like your gps uses the old datum (nad) in decimal (i had a iden phone that used that) also if you find it is in old datum format then you will know how to get better accuracy when seeking caches as well, them .003 can be a pain and maybe even put you on the wrong side of the creek in some places if your thinking its using wgs and its nad

 

Agreed. Unfortunately, I have no way of knowing which datum the unit uses. I've checked both of the manuals for any instance of 'wgs' 'nad' or 'datum' and came up with nothing. Suppose I'm going to have to get the NAD co-ordinates, and see if I'm able to find a cache I wasn't able to find previously. Guess I just kind of assumed that no one would be using the NAD datum any longer.

 

Thanks.

[+keehotee]

 

The biggest thing that stuck out to me in your post however, was the part where you indicated that you couldn't place your cache because it was within 37 feet of another cache. Caches must be at least 528 feet from other physical caches. So I'm not sure that this would be "corrected" by "more accurate" coordinates.

 

Sorry to drift O/T....

Reading the OP it seems to me that this was a "question to answer" stage of a multi rather than a physical cache?

His cache (part of a multi) takes the co-ordinates based on reading the plaque attached to the pedestal.

Can the OP confirm if this is the case? Or is it the case that the cache was still too close to the final co-ords of the multi?

[VE7RJT]

 

The biggest thing that stuck out to me in your post however, was the part where you indicated that you couldn't place your cache because it was within 37 feet of another cache. Caches must be at least 528 feet from other physical caches. So I'm not sure that this would be "corrected" by "more accurate" coordinates.

 

Sorry to drift O/T....

Reading the OP it seems to me that this was a "question to answer" stage of a multi rather than a physical cache?

His cache (part of a multi) takes the co-ordinates based on reading the plaque attached to the pedestal.

Can the OP confirm if this is the case? Or is it the case that the cache was still too close to the final co-ords of the multi?

 

Yes, there was no physical component to the other cache itself at the same location. The plaque on the wood carving only provided a clue to the final destination of the cache. It's fine. I've already moved my cache, hidden it again, and re-submitted.

[+keehotee]

 

The biggest thing that stuck out to me in your post however, was the part where you indicated that you couldn't place your cache because it was within 37 feet of another cache. Caches must be at least 528 feet from other physical caches. So I'm not sure that this would be "corrected" by "more accurate" coordinates.

 

Sorry to drift O/T....

Reading the OP it seems to me that this was a "question to answer" stage of a multi rather than a physical cache?

His cache (part of a multi) takes the co-ordinates based on reading the plaque attached to the pedestal.

Can the OP confirm if this is the case? Or is it the case that the cache was still too close to the final co-ords of the multi?

 

Yes, there was no physical component to the other cache itself at the same location. The plaque on the wood carving only provided a clue to the final destination of the cache. It's fine. I've already moved my cache, hidden it again, and re-submitted.

 

I thought the 1/10th mile proximity guideline only applied to physical cache containers? Can a passing reviewer confirm this?

[+niraD]

I thought the 1/10th mile proximity guideline only applied to physical cache containers? Can a passing reviewer confirm this?

I am not a reviewer, but I can confirm that the cache saturation guidelines apply to "[c]ache containers and physical stages", and do not apply to "[n]on-physical caches or stages including reference points, trailhead/parking coordinates and question to answer waypoints".

 

However, listing the coordinates of a plaque as "stage of a multi-cache" means that the cache saturation guidelines apply to it. To allow other caches to be placed near the plaque, the cache owner must list it as "question to answer" rather than as "stage of a multi-cache".

 

There used to be a knowledgebase article about additional waypoints, but I can't seem to find it now...