How to get accurate coords ?

[+Kry102001]

Hi all.

 

I have placed a series of 7 caches and three people have already found them, but, they have all reported the coords being off.

 

I used a Garmin 60CSx to obtain the coords when placing these caches, so, would going back and using the average function give me better coords or is it going to be impossible as the locations where the caches are located is very much covered by trees ?

 

Any help is appreciated as I want the coords to be as spot on as possible.

 

I also have an iphone and the geocaching app if that could help.

[+triga]

You should calculate average coordinates.

 

You can do this on the 60CSx by:

 

* marking your location (mark button),

* give it a name you can remember

* Go to Find -> Waypoints -> Your waypoint

* Press Menu -> calculate average (not sure, mine is in dutch)

 

It will start to do measurements (you will see a counter of how many) of your location. I usually take 15-20 before I fix it. The more you do, the more accurate it gets.

 

With lots of foilage, I'd go for 40-60

 

I wouldn't use the iPhone to mark a location, especially if you have such a fine device already ^^

[+Kry102001]

They have complained about the final cache coords being 50/60 feet away, so, I assume that I need to do the average thing to narrow it down so that people can get a better idea of where the cache is.

[+fizzymagic]

50 or 60 feet off is pretty bad, especially if you have a 60cx. I'd expect average accuracy of more like 10-15 feet if you have EGNOS, maybe 20 without. Unless the tree cover is quite thick, it should not have that big an effect.

 

I'd take multiple readings, moving at least 100 feet away between readings, and then perform a "smart" average on the results. Also, it helps to let the GPS sit at the cache location for a couple minutes before, and then average for a minute or so when you take the coordinates.

 

I've noticed that bad coordinates in my area have all but disappeared in the last couple of years with the advent of new GPS chipsets. Are you sure you're using the right datum? Should be WGS-84.

[+Harry Dolphin]

What I do is to walk away 50-70 feet. Then use the GPS to find my cache. Preferably a few times from different directions. If the GPs leads me right to the cache, then my QC department is happy. If not, I keep trying until I get it right. Yes. I do use averaging.

Even then, there can be problems. I hid one recently, using that method. The first few cachers mentioned that it was 30-40' off. (I blame it on the magnetite! That wreaks havoc on compasses. Not sure about satellite signals. And the deep mine shaft nearby.) So, I went back (met a very large bear on the way), and redid the coords. Changed them by 40.9 feet. Recent finders said the new coords were much better. So, even that method can have problems. I do try to leave fairly explicit hints (which helped the first finders.)

[+EscapeFromFlatland]

Are there any buildings, lots of trees, cliffs or other high terrain right near the cache?

I've found caches before where due to the cliff face there is lots of signal bounce and its hard to get coordinates at the site.

I even hid one next to a cliff face and tunnel that has a hard time getting a good signal.

[+The Blorenges]

We do a similar routine to Harry Dolphin, walking in on the location several times from different directions and then averaging out the co-ords.

 

Even then, if it's under heavy tree cover, it's worth giving a really helpful hint. (Make sure your tree identification skills are good! )

 

MrsB

[+Mom-n-Andy]

I put my 60csx in the place where the cache will be and press the MARK button. An AVG soft button should be displayed on the screen. Select that and let the gps stay in place for a few minutes. You will see the reading count increasing (1 every second) and hopefully the accuracy decreasing. I always let the gps average at least 100 readings and more under heavy tree cover. This usually results in 6-8 feet estimated accuracy.

 

Then I come back in a day or two and use the gps to lead me to the cache to check the coordinates.

 

When I first got the 60csx, I was playing with the average function and forgot that I left it running on the windowsill overnight. It recorded something like 50000 readings and had an estimated accuracy of .6 feet!

[+SSO JOAT]

The averaging function is often used poorly. You don't want to just turn on averaging and let the GPS sit there to see how many readings it can take. Just a couple "averaged" points that are way off will ruin the final result. It is much better to take about a dozen averaging readings and then verify the location as follows:

 

First, you need to make sure you turn the GPS on at least 15-20 minutes before you mark a waypoint. It takes awhile for it to download all the satellite data and start using all that info to calculate your position with the greatest accuracy. Turn it on in a clear sky zrea and check the satellite page. You should have a strong, solid bar under every satellite. If some are blinking, wait some more.

 

Move from the clear area to your cache site and get in the position to get the best sky view to the GPS. Check your satellite page to ensure you still have a good signal.

 

Press and hold the Enter key (Mark) and when the save waypoint screen pops up, activate the averaging function. Let it work for about 10 to 15 readings and save it. Now, look at the data field on the bottom to see how far it is to the waypoint. If you see that number grow by more than 6-8 feet, activate the average function again. Each time you initiate the average, it will throw out the previous one and start over. Repeat this process a couple times until the waypoint says you are within a couple feet, then save the waypoint.

 

Walk away. Navigate back to the point you just saved. If it brings you back, it's good to go.

[+briansnat]

If the cache is in an area with difficult reception averaging won't help much. I usually don't average my caches and my coordinates are fine (in fact many logs compliment them). The only caches where I get consistent complaints about coordinates are the caches where I averaged extensively (using a combination of the methods described by SSO JOAT and Fizzymagic above).

 

How could that be possible? Probably because the only time I average is when I'm having a hard time getting good coordinates. It is in areas with a poor signal or one conducive to multi pathing errors. So when I average I'm averaging bad data.

 

If you have good reception conditions then averaging is unnecessary, if you have lousy reception then it won't buy you much unless you are willing to return to the site repeatedly over a period of a few days. Even then there are no guarantees.

Edited March 26, 2010 by briansnat

[+Scuba4jews]

I have to average manually, does the Oregon 200 do it automaticly?

[The 2 Dogs]

I have never used the averaging function on my GPS. I simply mark the location, walk away and then try to find my own cache back. If it brings me back to the correct location a few times then that's all you need to do. I have had only good results from this method and I've place nearly 150 caches.

Edited March 26, 2010 by The 2 Dogs