GPS Accuracy?

[airhogs123]

I am new to geocaching and would just like to know what is the best way to get the most accurate coordinates out of my GPS when hiding or searching for a cache?

[namiboy]

i dont know about hiding, but when searching just put the listed coordinates into your gpsr however and that is the best you can do. remember, your gpsr will always be off by a bit, and the geocache hiders wil be off by a bit.

[+JBnW]

Some tips on getting the best accuracy out of your unit. Of course, make sure you have the latest firmware/software for the unit, fresh/recharged batteries, and allow your GPS (if new) to sit out for at least 30 minutes to receive good satellite data. If your GPS is capable, enable WAAS/EGNOS. As advertised, this will improve accuracy to 3-5 meters...YMMV. (Or is that, YMWillV??) Even so, you'll be more accurate with WAAS/EGNOS than without.

 

For placing, there's a couple options; either use the GPS's built-in Waypoint Averaging (if available), or collect several sets of coords over a few days at different times, and do simple math to get an average. Also, place your GPS where it has a good view of the sky, and let it set for several minutes to stabilize before marking the location.

 

For finding, remember that your GPS has some amount of error, as did the hider's. These errors add up. When you get within 50 ft of a cache, start paying less attention to the GPS and more attention to all the places the cache could be hidden.

 

Sometimes, the best way to improve accuracy is to know and work with/around the inherant inaccuracy.

 

Hope this helps, and good luck!

[+Wintonian]

For placing, there's a couple options; either use the GPS's built-in Waypoint Averaging (if available), or collect several sets of coords over a few days at different times, and do simple math to get an average. Also, place your GPS where it has a good view of the sky, and let it set for several minutes to stabilize before marking the location.

 

How to average - from the FAQ.

[airhogs123]

Thanks for the info!

[airhogs123]

Does anybody have any good tips for good accuracy? Should you hold the GPS a certain way or stand by certain structures or buildings to get more accuracy?

[+Reddgroom]

Does anybody have any good tips for good accuracy?

It's actually pretty easy. I have always cached with older GPS's (first a Garmin 45 circa 1994, now a Garmin GPS III plus circa 2002) but have always gotten good results with a few easy (and maybe obvious tips)

 

1. Don't store your GPS in your backpack or your pocket... put it out there where it can see the sky. If it has an antenna, let it point up. Don't put the GPS next to the cell phone or radio or other kind of electronic equipment that might cause interference.

 

2. On sunny days, you should get pretty good reception, on cloudy days, expect some variance and less accuracy.

 

3. Be a little patient. Stand still and let the coordinates settle to measure and average. If searching for a cache, put the GPS down on a rock or a wall and let it sit still for a few minutes while you look around.

 

4. Follow the numbers, not the arrow. When you get close to a cache, the arrow will flip back and forth as it thinks you are on either side of it. Pay attention to the exact coordinates you are searching for and use your GPS to make the numbers match. I like to think in terms of "Go more North.. or Go less West" to get the exact spot.

 

I wouldn't worry about trying too hard, most GPSers work pretty well and get you SUPER close. I can usually get within 10 feet or so of a cache without even trying too hard.

 

Get out there and try it a bit. The more familiar you are with your GPS unit, the better you can make it work for you.

[+briansnat]

Does anybody have any good tips for good accuracy? Should you hold the GPS a certain way or stand by certain structures or buildings to get more accuracy?

 

GPS units do perform better when held a certain way. It is usually dependent on the antenna in that unit. This was more important a few years ago before the advent of the high sensitivity receivers, but holding a GPS properly can still improve performance somewhat.

 

For instance the Garmin eTrex line, most Lowrance hand helds and the Magellan eXplorists use a patch antenna. Patch antennas are strongest picking up the sats directly overhead. so these units like to be held horizontally, face up to the sky. My experiments with the DeLorme PN40 lead me to believe that it also has a patch antenna.

 

Units like the Garmin Map 60 and 76 series and older Magellans (Meridian and Sportrak) have quad helix antennas. Quad helix antennas are better at picking up sats closer to the horizon. So these units perform best held vertically.

 

I'm not certain about what antennas are in the Garmin Oregon and Colorado, but if I had to guess, the Colorado's design suggests a quad helix, while the Oregeon likely has a patch.

 

Again, with the modern high sensitivity receivers, the position you hold the unit isn't all that important but you might see some very modest improvements in performance. Many older units however will see significant improvements when held properly.

[+StarBrand]

Does anybody have any good tips for good accuracy?

It's actually pretty easy. I have always cached with older GPS's (first a Garmin 45 circa 1994, now a Garmin GPS III plus circa 2002) but have always gotten good results with a few easy (and maybe obvious tips)

 

1. Don't store your GPS in your backpack or your pocket... put it out there where it can see the sky. If it has an antenna, let it point up. Don't put the GPS next to the cell phone or radio or other kind of electronic equipment that might cause interference.

 

2. On sunny days, you should get pretty good reception, on cloudy days, expect some variance and less accuracy.

 

3. Be a little patient. Stand still and let the coordinates settle to measure and average. If searching for a cache, put the GPS down on a rock or a wall and let it sit still for a few minutes while you look around.

 

4. Follow the numbers, not the arrow. When you get close to a cache, the arrow will flip back and forth as it thinks you are on either side of it. Pay attention to the exact coordinates you are searching for and use your GPS to make the numbers match. I like to think in terms of "Go more North.. or Go less West" to get the exact spot.

 

I wouldn't worry about trying too hard, most GPSers work pretty well and get you SUPER close. I can usually get within 10 feet or so of a cache without even trying too hard.

 

Get out there and try it a bit. The more familiar you are with your GPS unit, the better you can make it work for you.

Sorry but I have to dispute several points here:

 

1. Very good advice!

 

2. The frequencies chosen for GPS signals were delibertly chosen due to the fact that clouds will not affect the signal in a negative way.

 

3. While older receivers certain benefit from needing a moment to settle down - more modern ones with fast processors should have your position calculated much more quickly.

 

4. Follow the compass arrow until you are within 20 feet or so and then put the unit away and look for likely hiding spots. The accuracy of our handheld units is generally in the range of 20 - 25 feet and closer then that does get varible. Do not pay much attention to the accuracy reading on the unit as that is an EPE (Estimated Position Error) - just an estimate with low confidence. The arrow swings around because the numbers for the coordinates swing a bit - the 2 are tied very directly together. You have no idea what kind of error the hider hads so be prepared to widen the search area up to 40 or more feet from where your unit says ground zero is. Most caches are found within 15 feet or so but do be prepared to widen your search. If necessary back off from another direction and pull out the GPS again to verify what area it is pointing at.

[airhogs123]

What could affect the accuracy of the GPS device?

[+Trucker Lee]

What could affect the accuracy of the GPS device?

The number of sats being received

Signal getting blocked by being too close to structures

[+Trucker Lee]

What could affect the accuracy of the GPS device?

The number of sats being received

Signal getting blocked by being too close to structures

[+TrailGators]

What could affect the accuracy of the GPS device?

The number of sats being received

Signal getting blocked by being too close to structures

That pretty much sums it up. The satellite screen will show you how many satellites are visible and the resultant accuracy.

[airhogs123]

What should or shouldn't I be standing by that could help, block or interfere with the signal?

[+StarBrand]

What should or shouldn't I be standing by that could help, block or interfere with the signal?

Actually you are the biggest problem!! The human body is quite good at blocking the signals.

 

Hold the unit out from your body or clip it to a shoulder of a pack or something to minimize how many sats you are blocking (some of us block more than others )

[+Rockin Roddy]

I don't do any of the steps outlined and I have never heard a peep about accuracy. All I do (or did before I got the PN-40) was put my GPS down near the hiding spot and walk away fro about 5 minutes. When I come back, I mark the location and then walk away. After I get a good distance away, I walk back, allowing the GPS to lead me to the spot. if it's close, I'm out of there!

 

Did that for around 80+ caches and only heard complaints in the beginning when I had the old etrex yellow (junk IMHO).

 

Now, I want to address one of Briansnat's comments...I don't think the PN-40 has a patch antenna (but could be wrong)...I get WAAS locks when I have my unit laying flat (like the other day when I had it on my motorcycle...my "mount" is a velcro strip attached to the gas tank).

 

On the PN-40, I simply walk up andhit the average button, let it do it's thing for about a minute or less and call it a day.

 

The days of taking several readings over different times and days are over IF you own a newer tech GPS. The old etrex lines and old Magellans might require you to take the extra steps, but not the new ones! And truly, being a few feet off isn't going to matter, but being 15-20 feet off is a bit much!

 

I'll probably catch flak for this post, but seriously, how hard is it really?

[+StarBrand]

.... being a few feet off isn't going to matter, but being 15-20 feet off is a bit much!

 

...

Actually the general accuracy of our handheld units is in the 20 - 25 foot range. The EPE reading on most units is for an accuracy with only about a 60% confidence level. Not terribly unusual to have reading off by 15 - 20 feet. Thats well within the area I would be searching.

[+Rockin Roddy]

.... being a few feet off isn't going to matter, but being 15-20 feet off is a bit much!

 

...

Actually the general accuracy of our handheld units is in the 20 - 25 foot range. The EPE reading on most units is for an accuracy with only about a 60% confidence level. Not terribly unusual to have reading off by 15 - 20 feet. Thats well within the area I would be searching.

 

This I know...but think about how I said that. If MY reading is off by 15-20 feet and the EPE is another 15-20 (or 30 as is the standard I believe) feet off, I am putting people too far away. That's why I said a few feet (IN YOUR READING) is OK, but not much more!

 

I'll also point out that (for my GPS at least) I don't believe there's that big of an error in accuracy. I have checked my unit against a benchmark a few times and the worst so far has been 1.2'. So, again, the older units might not be as accurate, but I think the new ones are much better than they are rated for (in other words, the rating might be merely to cover their arses should you find a worse reading). Again, this is MHO, YMMV and I won't deny that readings are different in other areas and under different conditions! I am only reporting MY experience and cannot speak for others!

 

ETA: Their being the manufacturer...

Edited March 19, 2009 by Rockin Roddy

[+StarBrand]

.... being a few feet off isn't going to matter, but being 15-20 feet off is a bit much!

 

...

Actually the general accuracy of our handheld units is in the 20 - 25 foot range. The EPE reading on most units is for an accuracy with only about a 60% confidence level. Not terribly unusual to have reading off by 15 - 20 feet. Thats well within the area I would be searching.

 

This I know...but think about how I said that. If MY reading is off by 15-20 feet and the EPE is another 15-20 (or 30 as is the standard I believe) feet off, I am putting people too far away. That's why I said a few feet (IN YOUR READING) is OK, but not much more!

 

I'll also point out that (for my GPS at least) I don't believe there's that big of an error in accuracy. I have checked my unit against a benchmark a few times and the worst so far has been 1.2'. So, again, the older units might not be as accurate, but I think the new ones are much better than they are rated for (in other words, the rating might be merely to cover their arses should you find a worse reading). Again, this is MHO, YMMV and I won't deny that readings are different in other areas and under different conditions! I am only reporting MY experience and cannot speak for others!

 

ETA: Their being the manufacturer...

Fair enough - I think I understand what you were saying!!

[+Rockin Roddy]

Fair enough - I think I understand what you were saying!!

 

[airhogs123]

Is the weather a huge factor in accuracy? Any more tips or tricks anyone has that will be helpful to get the most accuracy?

Edited March 31, 2009 by airhogs123

[mickbritt]

As far as accuracy. Some models are better than others obviously. Try walking very slow while searching, holding the GPS in front of you without swinging or swaying it with you arm. Also for best accuracy, check the sat screen on you gps and you will see how many sats you are pickin up, the more the better.

[+Fuchsiamagic]

What should or shouldn't I be standing by that could help, block or interfere with the signal?

I used to carry a Canon EOS camera with an auto-focus 400mm lens in my backpack and wondered why my GPSr kept pointing in different directions! The lens has magnets and electric motors in it. As soon as I left the camera at home, it was fine!

[airhogs123]

Thanks for the help guys! Any more tips or tricks from anyone? The more I know the better.

[+Fuchsiamagic]

Thanks for the help guys! Any more tips or tricks from anyone? The more I know the better.

Most of what you need to know has been covered here, but the best way to learn is get out there with your GPSr and play with it! Mark some waypoints and go back and check their positions several hours and days later and you will see how the accuracy varies. Some days it will be spot on, others over 20 feet away.

 

One point that was touched on is to enable WAAS/EGNOS if your GPS is capable. In addition to the 27 - odd GPS satellites which change their position regularly, there are three geosationary satellites orbiting the equator which your reciever can make use of if you can see the horizon. This will bring the accuracy right down, but remember the cache setter might not have done a very good job so in that case you will be wasting your time.

[+Kohavis]

I don't think this has been mentioned yet, but you can really do everyone a favor if you use waypoint averaging when hiding a new cache, if your GPSr has that capability. Most do.

 

Take about 100 readings while standing as close to the cache as possible and let the unit average them. It only takes a couple of minutes. You can watch the error margin drop as it takes more readings. The folks who log the finds will appreciate it and usually comment on how accurate the coordinates were

[airhogs123]

How do you know if your GPS has waypoint avergaing?

[airhogs123]

How do you know if your GPS has waypoint avergaing?

 

Any help here guys?

[jholly]

How do you know if your GPS has waypoint avergaing?

 

Any help here guys?

 

If it is a garmin, when you you press mark you have the option of avg on the bottom of the screen.

 

Jim

[+Bear and Ragged]

Thanks for the help guys! Any more tips or tricks from anyone? The more I know the better.

 

Yep.

Get out there and try to find a few!

After a while you get a "Cachers Eye" about where things are hidden.

[airhogs123]

How do you know if your GPS has waypoint avergaing?

 

Any help here guys?

 

If it is a garmin, when you you press mark you have the option of avg on the bottom of the screen.

 

Jim

 

It is a Garmin GPSMAP 60csx.

[jholly]

How do you know if your GPS has waypoint avergaing?

 

Any help here guys?

 

If it is a garmin, when you you press mark you have the option of avg on the bottom of the screen.

 

Jim

 

It is a Garmin GPSMAP 60csx.

 

Like I said, do a Mark and on the bottom is a selection for AVG. Scroll over to the AVG, press enter and your now in the average mode. When your done press save.

 

Jim

[+mrbort]

Tropospheric delays (caused by clouds) will affect the accuracy of the signal but will generally be secondary to the chipset limitations of commercial receivers, especially if you have a severely lopsided satellite constellation in view. If this is the case, you're going to be facing more prominent errors anyway so the most important thing is that the unit has the clearest view of sky possible (hold it away from you or even better set it down on a rock and walk away for a bit). You'll certainly (like others have said) be able to get a good feeling for how accurate your unit is by just going out there and finding caches. Sometimes you'll trust your unit not enough and sometimes you'll trust it too much. Waypoint averaging doesn't really do that much as the constellation of satellites doesn't change on the minute scale timeframe. However, it's a good thing to let it sit there and self calibrate for a few minutes (and then if you're keen on the averaging, have at it) before you mark. Before you set into averaging or anything first make sure you have the best view of the sky possible from that location then let the unit sit and work out the changing signals it's receiving. If you start averaging right away, you'll add in the bias that will be there from an incomplete, unincorporated satellite constellation...

 

I'm mostly spouting and extrapolating from GPS theory with which I have worked during graduate school and my professional career.... As for waypoint marking for geocaching with commercial handheld units, i'm still new but have some ideas about what should work. It's science after all!

 

Good luck!

[airhogs123]

Would I use this averaged number from the GPS if I where to place a cache?

[airhogs123]

Would I use this averaged number from the GPS if I where to place a cache?

[+Pork King]

What could affect the accuracy of the GPS device?

 

I'm not sure if there's any truth to it or not, but on some days that the ole GPS seems to not cooperate, I've heard tell that the local Air Force Base occasionally "scrambles" GPS signals in training excercises.

 

Can anyone confirm or refute this?

[+smithdk]

Would I use this averaged number from the GPS if I where to place a cache?

 

I average my numbers when getting coordinates . Once I have it marked. I will usually walk away from the spot and then return to it from another direction to see how close it brings me to it. I make any adjustments if necessary. I will also try to check it again on a different day if possible.

Edited April 11, 2009 by smithdk

[+BrrrMo]

Some tips on getting the best accuracy out of your unit. Of course, make sure you have the latest firmware/software for the unit, fresh/recharged batteries, and allow your GPS (if new) to sit out for at least 30 minutes to receive good satellite data. If your GPS is capable, enable WAAS/EGNOS. As advertised, this will improve accuracy to 3-5 meters...YMMV. (Or is that, YMWillV??) Even so, you'll be more accurate with WAAS/EGNOS than without.

 

For placing, there's a couple options; either use the GPS's built-in Waypoint Averaging (if available), or collect several sets of coords over a few days at different times, and do simple math to get an average. Also, place your GPS where it has a good view of the sky, and let it set for several minutes to stabilize before marking the location.

 

For finding, remember that your GPS has some amount of error, as did the hider's. These errors add up. When you get within 50 ft of a cache, start paying less attention to the GPS and more attention to all the places the cache could be hidden.

 

Sometimes, the best way to improve accuracy is to know and work with/around the inherant inaccuracy.

 

Hope this helps, and good luck!

 

Cute Avatar, does the Garmin 60CSx have the WASS/EGNOS feature? There documentation is a little lite on info>

[+smithdk]

What could affect the accuracy of the GPS device?

 

I'm not sure if there's any truth to it or not, but on some days that the ole GPS seems to not cooperate, I've heard tell that the local Air Force Base occasionally "scrambles" GPS signals in training excercises.

 

Can anyone confirm or refute this?

 

I'm in the Air Force and have been caching for over 3 years. Both of my GPSrs has never acted up yet.

[airhogs123]

Is it worth it to put on WAAS?

[+The Blorenges]

I would say yes, enable WAAS it does improve accuracy. If you want to find out a bit more about WAAS and GPS accuracy I've put some info together on my resource website - this is aimed at cachers in the UK and not the US/Canada but the information is the same. Note that in Europe WAAS is called EGNOS. The information about how the groundstations work is the same for outside of Europe but obviously the US/Canada has different locations but they do the same thing.

 

www.follow-the-arrow.co.uk/resources/ (follow the link to GPS and Coords)

 

Chris (MrB)

[airhogs123]

Does WAAS use more battery?

[+Team Cotati]

Does WAAS use more battery?

 

Of course it does. However in my opinion, not enough to be noticeable or worth worrying over.

 

WAAS provides better accuracy at close to zero cost, just turn it on and do not fret over it.

 

From the Garmin www site:

 

You've heard the term WAAS, seen it on packaging and ads for Garmin® products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.

 

The origins of WAAS

 

The Federal Aviation Administration (FAA) and the Department of Transportation (DOT) are developing the WAAS program for use in precision flight approaches. Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity, and availability. WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing, and satellite orbit errors, and it provides vital integrity information regarding the health of each GPS satellite.

 

How it Works

 

WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

 

Who benefits from WAAS?

 

Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of WAAS is that it does not require additional receiving equipment, while DGPS does.

 

Other governments are developing similar satellite-based differential systems. In Asia, it's the Japanese Multi-Functional Satellite Augmentation System (MSAS), while Europe has the Euro Geostationary Navigation Overlay Service (EGNOS). Eventually, GPS users around the world will have access to precise position data using these and other compatible systems.

 

It just keeps getting better

[airhogs123]

Anymore tips/suggestions/tricks for good accuracy?

[airhogs123]

Anymore tips/suggestions/tricks for good accuracy?

[+KD7MXI]

turn off maps - those things slow my etrex legend way down - i also turn off waas etc to save memory on my gps - saving memory and processing time helps from time to time