Is there an GPS unit that will get me within 10 feet of a site?

[fongu]

I pulled up the foundation of an old house that used to be in a field and found settings that I could use with a gps, but have none at this time. went to this field Saturday and couldn't find it. going back this weekend with the map I pulled off the satellite maps.

 

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[eyemustdigtreasure]

Assuming that you live in the USA and specifically the southern portion of the continental USA, any GPS receiver that has Wide Area Augmentation System (WAAS) capability and can see one of the two satellites should get you better than 3m. If you are near an airport you may get 1m accuracy.

Usually around thirteen satellites are dedicated to WAAS, if you are lucky.
Keep out from underneath heavy timber, and away from direct contact of cliff faces
and buildings, to get good accuracy.
Oh, by the way, your Horizontal Datum should be same as when the waypoint
on the sites were set....could mean hundreds of feet difference...!
If you used a hard-copy topo map, there will be a notation what everything is set-to
on the sheet....

 

[Tinhorn2]

I use my old GPS to find places, usually within 10 or 20 feet but the satellites have to be around me right [I agree with Sidevalve45 & eyemustdigtreasure]
Also, my GPS don't know where North is unless I am walking (or driving) but it tells me the "bearing" so I use a compass.

my old GPS is an etrex Venture Garmin & I really like my compass, it says Silva type 7 NL on it. It is better than my old military one LOL

 

[eyemustdigtreasure]

Usually around thirteen satellites are dedicated to WAAS, if you are lucky.
Keep out from underneath heavy timber, and away from direct contact of cliff faces
and buildings, to get good accuracy.
Oh, by the way, your Horizontal Datum should be same as when the waypoint
on the sites were set....could mean hundreds of feet difference...!
If you used a hard-copy topo map, there will be a notation what everything is set-to
on the sheet....

Forgot to add that when setting waypoints, find the best accuracy, set the point, then use "Averaging" to get even better closure, and the longer you wait, the better it gets (usually)...! ....then click "Save"

 

[eyemustdigtreasure]

Forgot to add that when setting waypoints, find the best accuracy, set the point, then use "Averaging" to get even better closure, and the longer you wait, the better it gets (usually)...! ....then click "Save"

Add that once you find poor accuracy in heavy tree canopy then follow your separate compass on the same bearing you’ll get there!

 

[lostcoast]

GPSMAP 66SR and 65S have multiband and advertise 6 ft accuracy. Best currently available for civilians as of 2021.

 

[golddigger14s]

The OP hasn't been here since 2013.

 

[Clay Diggins]

GPSMAP 66SR and 65S have multiband and advertise 6 ft accuracy. Best currently available for civilians as of 2021.

Wow that's news! Could you point me to where garmin claimed 6 foot accuracy for any of their commercial handheld devices? To date I don't know of any company to come even close to that level of accuracy with a commercial unit.

This must be some crazy new technology.

 

[lostcoast]

Wow that's news! Could you point me to where garmin claimed 6 foot accuracy for any of their commercial handheld devices? To date I don't know of any company to come even close to that level of accuracy with a commercial unit.

This must be some crazy new technology.

It's on the screen of the unit when showing what satellites its connected to (unit on the right, 1.8 meters):

In addition to multi-GNSS (using GPS, GLONASS, and GALILEO), they're utilizing multiband support, adding the L5 frequency supported by newer GPS satellites. That's where the increased accuracy is gained. To my knowledge, the only non military devices in the US that can do this are currently the GPSMAP 65S and 66SR.

A review of the GPSMAP 66SR talks about this a bit and the compares the accuracy to other devices (GPSMAP 66i, IPhone 12, Fenix GPS watch).

 

[RTR]

Although this thread is 10 years old, someone might still be asking the original question in the OP.... Autopilot with "Return home" GPS Will get you w/in inches. Thinking this system could be modified to work.....
>> https://www.dronethusiast.com/auto-return-drone/

 

[Clay Diggins]

It's on the screen of the unit when showing what satellites its connected to (unit on the right, 1.8 meters):

View attachment 1997401

In addition to multi-GNSS (using GPS, GLONASS, and GALILEO), they're utilizing multiband support, adding the L5 frequency supported by newer GPS satellites. That's where the increased accuracy is gained. To my knowledge, the only non military devices in the US that can do this are currently the GPSMAP 65S and 66SR.

A review of the GPSMAP 66SR talks about this a bit and the compares the accuracy to other devices (GPSMAP 66i, IPhone 12, Fenix GPS watch).

OK I didn't think Garmin was silly enough to claim 6 foot accuracy. The review is like many I have read. The guy likes his GPS unit and it does look like a nice one.

If you read the article for the actual comparison data he collected along his grand canyon trail test:

The Garmin 66sr unit was 94% accurate.​

The Fenix 6s pro solar was 93% accurate.​

The Garmin 66i unit was 91% accurate.​

The iPhone was 87% accurate.​

​

The Garmin 66sr came closest on distance with a 1.4 mile distance error over the 23.2 mile trail.

The Precision was slightly better than the other GPS units tested but the margin for precision error was about the same as the others.

I've written software for, and tested, many GPS units over the last 12 years or so. The results you see above from the article are typical for most GPS units I've tested in that time.

The testing of GPS against aerial photos is inherently inaccurate. Aerial photos have a margin of error on flat land of about 30 foot. In steep terrain that error goes way up. Without measurement in relation to known control points any estimation of accuracy is purely anecdotal.

As a practical matter when testing I've found the antenna design and the placement of the unit in relation to nearby objects, including your body, has more effect on the accuracy of readings than the chipset or any whiz bang features. If the person who wrote the article had mounted the GPS units along the same horizontal plane and in the same relationship to the person carrying it I'm sure you would see the differences between the units tighten up considerably.

The reason Garmin, and the other GPS manufacturers don't use accuracy as a selling point is because GPS units are measuring devices. Measuring devices are subject to ISO standards of accuracy for measurement. That's a tough standard to excel in for GPS units because the ISO standard uses both accuracy and precision to calculate the resulting accuracy figures. When using that standard all GPS units will at best reflect the base system accuracy of 10 meters (33 feet).
You can read more about accuracy and precision here:

Here Is the Difference Between Accuracy and Precision

Accuracy is how close a measurement is to the true value, while precision is how consistently you get the same measurement under the same conditions.

www.thoughtco.com

The GPS satellite timing systems have been improved over time. That results in better positional accuracy for all units in ideal conditions. When conditions are not optimal the number of signals, signal cohesion, antenna design, dwell time and operator placement become the determining factors in accuracy. The only improvement a manufacturer can bring in that more typical use situation is improved antenna design.

After years of testing I prefer Garmin manufactured units. They are robust with generally good design and most handheld units have good antennas. If I were looking for a new GPS unit I would definitely consider one of these units.

 

[Rawhide]

Just purchased a new GPS Garmin 66i. Needed something with a emergency button and was floored at the price, things have went up. Also the monthly subscription was pricey. Then you had to buy a pricey card for the state you want to hunt in. I can understand why a person would want to be that close, so will let you know when I use it for that. Older gps units never let me down so Im not sure what your gps is doing.

 

[lostcoast]

OK I didn't think Garmin was silly enough to claim 6 foot accuracy.

 

[Clay Diggins]

View attachment 1997674

Wow thanks for the effort to point that out. I did see it in the original but you really brought out the reliability feature on the GPS unit.

I'm sure you know more about this than I do, after all you seem to be capable of highlighting a picture - that's like magic or something! I guess you really showed that DA smart guy huh?

Let's look at what the Garmin engineer has to say about the reliability rating you are pointing out:

"Reliability is the mathematical confidence in the accuracy numbers the receiver is telling you. Accuracy is generally thought of as the error from the true point. However, if the receiver knew the exact error from the true point, it would just give you the true point. Instead the receiver uses the measurement consistency to indicate how accurate the position is. The consistency between measurements is what indicates the reliability. If all the measurements agree, then you can generally think that you have a reliable and trustworthy solution. If the measurements don’t really agree, then you may not be very confident about the accuracy metric. Generally, there is a trade-off in accuracy and reliability. To get more reliability (or confidence), you generally have to give a less accurate indicator. All of this doesn’t change the coordinates the receiver is computing — just the receiver’s confidence about those coordinates."

So according to the people who built the unit they can't give you the true point measurement (accuracy) but they can tell you whether the measurements you are receiving are consistent (precision). True consistency is the same as precision. Precision doesn't measure how accurate the reading is but it does measure how consistent the reading is. As the engineer points out the GPS unit has no way of knowing how close to the true position it's measuring (accuracy) but it can tell if sequential readings are consistent (precision).

Being not such a smart guy I learned about GPS units by studying and testing. And that is why I provided the link previously about the difference between accuracy and precision. It's critical to know the difference when studying measurements. Which is what the Garmin engineer is writing about. Here's that link again and a cool picture of just what the difference between accuracy and precision is.

Here Is the Difference Between Accuracy and Precision

Accuracy is how close a measurement is to the true value, while precision is how consistently you get the same measurement under the same conditions.

www.thoughtco.com

So even though the Garmin unit calculates precision it has no way to know how accurate the reading is (see above). Instead it displays it's confidence in the precision of it's measurements.

 

[delnorter]

Very good Barry. While reading your replies I was thinking, “show him a shooting target for explanation”.
You did.

The surveying and aerial mapping company I worked for (eventually becoming manager of) were one of the first private sector companies to utilize the “new” Trimble Navigation GPS unit’s. Truly revolutionary technology.

Mike

 

[lostcoast]

So even though the Garmin unit calculates precision it has no way to know how accurate the reading is (see above). Instead it displays it's confidence in the precision of it's measurements.

Thanks for the detailed explanation. Most of my experience with GPS is the 90's era military PLGR unit. I'm more of a compass/map kinda guy. The Garmin is the first mapping GPS I've owned.

 

[Gare]

I have 3

Garmin GPSMAP 60CSx's and they are usuALLY within 10 to 15 feet. They are fairly inexpensive now​

 

[Clay Diggins]

I have 3

Garmin GPSMAP 60CSx's and they are usuALLY within 10 to 15 feet. They are fairly inexpensive now​

Agreed.

The GPSMAP 60CSx is my favorite handheld GPS unit. Lightweight, small, tough, easy on batteries, great antenna, right price, as accurate as any other handheld gps unit available, easy to read screen and, really important to me, can be operated with one hand while moving.

There are much larger screens and more functions on many gps units today than you will find on the Garmin GPSMAP 60 CSx. For some purposes those features might be a better unit for you. No GPS unit is right for everyone. But for an overall dependable and tough gps unit it's hard to beat the GPSMAP.

 

[Gare]

I might also add very easy to learn and use

 

[Gare]

I now use Gaia GPS it is pretty decent and accurate