GPS Accuracy

 

Tonight, I was watching my unit find the satellites and watching the accuracy change. The best i got was 12 foot. I was wondering, what is the best accuracy these units can achieve with good reception? Also was watching the elevation for about an hour in a stationary position and watched it continually decrease, about a foot every 5 minutes or so till it finally stopped. Was wondering how accurate that actually is.

That's about what I get typically

I usually see about 12 feet accuracy.

The best has been 8 ft on a beach, with no obstacles around and a perfectly clear day.

Vertical accuracy is not that great, I don't pay too much attention to it other than to get an idea of where I am.

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GPSMAP64s, iPhone XR w/Garmin North America, Yaesu VX-8R w/GPS.

sounds pretty good--

12 feet is around 3.6 meters, and for single-frequency GPS, that's pretty good. You didn't say how many birds you had in view, whether you had WAAS turned on (and one of the WAAS birds in view).

Altitude is a different story. Altitude is harder, and is going to fluctuate more. Altitude is a funny number calculated as an offset from an artificial geoid.

What I look for in GPS measurements is repeatability -- once I survey/store a reading, am I going to get results close to that the next time I'm in the same place? Just about any modern GPS receiver will pass that test if you can get a stationary reading over a minute or so with a clear view of the sky.

bob in very rainy silicon valley

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Nuvi 2460, 680, DATUM Tymserve 2100, Trimble Thunderbolt, Ham radio, Macintosh, Linux, Windows

.

I usually see 3 meters reported, with 10-11 sats on the unit going through the mountains.

--
nüvi 3790T | nüvi 775T | Those who make peaceful revolution impossible, will make violent revolution inevitable ~ JFK

No problem

I didn't have a problem today.

--
Val - Nuvi 785t and Streetpilot C340

See this post

Already been discussed here.
http://www.poi-factory.com/node/31650

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Nuvi 2460LMT.

don't pay much attention

knuceme wrote:

Tonight, I was watching my unit find the satellites and watching the accuracy change. The best i got was 12 foot. I was wondering, what is the best accuracy these units can achieve with good reception? Also was watching the elevation for about an hour in a stationary position and watched it continually decrease, about a foot every 5 minutes or so till it finally stopped. Was wondering how accurate that actually is.

I don't pay much attention to accuracy, all of the manufactures use a different mathematical formula to figure it. I used to use an iFinder Hunt for geocaching and a friend was using an older Garmin 76. His would be showing him 12 or 13 foot accuracy and my Hunt might be showing me 30 or 35 foot accuracy, yet the number of feet to the cache showing on each GPS might only be a foot or two different. The biggest difference I can see between the newer and older units is the chip sets, the more birds you can lock usually means better accuracy.

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Anytime you have a 50-50 chance of getting something right, there's a 90% probability you'll get it wrong.

GPS Averaging

On some devices the location wanders quite a bit, so to plant a geocache there are apps available for smart phones that average the location over an interval of time to get a better reading.

Its all relevant

When geocaching, the "hunt" to find the cache is the adventure. If we walked up to every one of them there would be no fun at all.

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Nuvi 2460LMT.

Geocaching

pwohlrab wrote:

When geocaching, the "hunt" to find the cache is the adventure. If we walked up to every one of them there would be no fun at all.

It is certainly a challenge when you are in an area with tall pine trees. At time I have had to give up because the inconsistent output of the GPS.

What I do

Mike107 wrote:
pwohlrab wrote:

When geocaching, the "hunt" to find the cache is the adventure. If we walked up to every one of them there would be no fun at all.

It is certainly a challenge when you are in an area with tall pine trees. At time I have had to give up because the inconsistent output of the GPS.

It certainly is a challenge when you can't get a good signal. I go back to where I have a good signal with direction and then pull out the compass I carry and pace it off.

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Nuvi 2460LMT.

Lets talk accuracy

I was going to purchase an update for my garmin.
Price $80.00..I was going to do it 2yrs ago..but this is why I did not..
Before I was going to buy the 2011 update, I called garmin, asked if certain fastfoods have now been added in my location
that have been in business for over 5 years. Reply was
"no they have not"....I would have to fill out a report and send it in.....Hey! I said ...you want me to pay $80.00 for an update that is incomplete and tell you whats wrong with it??? YOu want me to do the leg work
and not pay me for helping to make your product better?
Something is wrong with this Picture...Sorry she said
thats the way it works..
Well I check with other MFG's and would you belive???
They all do it,,,some just alittle different...some offer 4 (FREE) updates for the year....but wait till the following year.
You know people...We should demand that updates be viewed on a website before buying.
Thats just my opinion!

geocaching

A few years ago we tried geocaching. I would slowly walk to the latitude, then walk to the longitude. It was too easy. On each of the locations I was spot on, or off less than a few feet. I was using my hand held Magellan.
The altitude is erratic on all my units. Watching the altitude on a canoe trip down a river becomes hilarious.

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1490LMT 1450LMT 295w

Notice

Notice that geocaching and the fast food pois point out that 'accuracy' can be a relative term.

The geocachers are interested in how repeatable the point coords are a)between various units and b)on the ground without reference to a particular map.

Road and/or poi accuracy on the other hand, now throws in the repeatability of point coords between map plots (pois, road & other object placement) either within the same mfr's versions or between map producers (Garmin, Google, etc).

--
It's about the Line- If a line can be drawn between the powers granted and the rights retained, it would seem to be the same thing, whether the latter be secured by declaring that they shall not be abridged, or that the former shall not be extended.

Curious

k6rtm wrote:

You didn't say how many birds you had in view, whether you had WAAS turned on (and one of the WAAS birds in view).

It has never been clear to me if Garmin nuvi's use WAAS. And if they do, how can you tell from the satellite signal screen if you are locked on to a WAAS satellite?

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Alan - Android Auto, DriveLuxe 50LMTHD, Nuvi 3597LMTHD, Oregon 550T, Nuvi 855, Nuvi 755T, Lowrance Endura Sierra, Bosch Nyon

Accuracy

I have had 8ft at the stand still (it varies with movement) and figure it is close enough for me.
If I can't see where I am at that distance, I better not be driving and should get a dog and a cane.

--
Don't sweat the petty things and don't pet the sweaty things!

WAAS--

alandb wrote:
k6rtm wrote:

You didn't say how many birds you had in view, whether you had WAAS turned on (and one of the WAAS birds in view).

It has never been clear to me if Garmin nuvi's use WAAS. And if they do, how can you tell from the satellite signal screen if you are locked on to a WAAS satellite?

Most of the newer units can use WAAS.

On the 660/680 you have an option to enable WAAS/EGNOS.

On the sat position display, look for birds 48 and/or 51, those are WAAS

On some GPS units, enabling WAAS may increase power consumption, leading to shorter battery life if you're running on the internal battery.

--bob in silicon valley

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Nuvi 2460, 680, DATUM Tymserve 2100, Trimble Thunderbolt, Ham radio, Macintosh, Linux, Windows

Interesting information, and thanks for the response.

Neither of my Nuvi's (755T, 855) have the option to enable WAAS. I don't recall ever seeing a satellite with a number as high as 48 or 51. So I suppose that means these two models don't support WAAS, or maybe if they do they just don't display it on the sat signal screen.

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Alan - Android Auto, DriveLuxe 50LMTHD, Nuvi 3597LMTHD, Oregon 550T, Nuvi 855, Nuvi 755T, Lowrance Endura Sierra, Bosch Nyon

Anything above 32

alandb wrote:

I don't recall ever seeing a satellite with a number as high as 48 or 51.

The magic dividing line is just after 32.

A standard GPS bird in active service is assigned a PRN between 1 and 32, and this is what Garmin displays for them on the satellite page. (the SVN is unique to a physical bird, while PRNs get reused).

For the WAAS birds the NMEA convention is to designate the satellite number as the PRN minus 87, and this is what the Garmin units I'm aware of display for them. I presume there is a rule of not allocating a PRN to a WAAS bird lower than 87+33=120.

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personal GPS user since 1992

So archae86...

what you are saying is that the PRN is different than the SVN but similar to the WAAS, which by the way should not be confused with the NMEA? My only comment on your post is "Huh"? shock

So archae86...

sorry, I couldn't resist... cool

lucky

spokybob wrote:

A few years ago we tried geocaching. I would slowly walk to the latitude, then walk to the longitude. It was too easy. On each of the locations I was spot on, or off less than a few feet. I was using my hand held Magellan.
The altitude is erratic on all my units. Watching the altitude on a canoe trip down a river becomes hilarious.

You must have been extremely lucky. Usually the way it works is the person that hides the cache might be 20 feet off on his coordinates, then the person that's looking for the cache might be off 20 feet or more in the opposite direction. Now you have a 40 foot error. Or if you're lucky you are both off in the same direction. We had one guy hiding caches that were always at least 30 feet off according to everyone's GPS, One cache he put out was 190 feet off. Usually when I get between 25 and 30 feet from the cache, I put the GPS away and just start looking.

--
Anytime you have a 50-50 chance of getting something right, there's a 90% probability you'll get it wrong.

Exactly

Timantide wrote:

I have had 8ft at the stand still (it varies with movement) and figure it is close enough for me.
If I can't see where I am at that distance, I better not be driving and should get a dog and a cane.

Even though most addresses are usually at least two houses off I tell people that aren't familiar with using a GPS, if someone gives me an address in a large city 1000 miles away and the GPS gets me a couple of hundred feet from it, and I can't find it then I have no business traveling.

--
Anytime you have a 50-50 chance of getting something right, there's a 90% probability you'll get it wrong.

In Dash GPS

On a good day in the plains of Alberta I max out at 3 meters. Going in to the mountains of B.C. it drops to about 5 meters.

10 FOOT ACCURACY IN 30 SECONDS..!!

30 Seconds in time & 10 foot Accuracy..!!

My Nuvi 1300 WT GPS has been sitting on a shelf in my computer room/office for the past three plus months now. I just picked it up and walked out front door into the middle of the country road that runs past the house. Turned it on, waited for the splash screen.. and after the main screen came on I pressed the upper left corner of the screen and started counting.

It took between 20 to 30 seconds to acquire all 10 satellites. Sats #3,6,13,16,19 & 20 were all above 75%.. while #'s 20,25,30 & 31 were at 100%. It also showed a accuracy of 10 feet.

By the time one and a half to two minutes went by I had a accuracy of between 3 to 4 feet with all satellites showing 100%. I would guess it would depend on the time of day or night.. and the weather conditions.

Nuvi1300WTGPS

--
I'm not really lost.... just temporarily misplaced!

?

You had a 1 - 1.3 meter accuracy?

--
nüvi 3790T | nüvi 775T | Those who make peaceful revolution impossible, will make violent revolution inevitable ~ JFK

.

If you want to find out the true accuracy of your gps unit you could go to an NGS marker and compare the known coordinates to the gps coordinates.

Where's the doorbell?

Don B wrote:

Even though most addresses are usually at least two houses off I tell people that aren't familiar with using a GPS, if someone gives me an address in a large city 1000 miles away and the GPS gets me a couple of hundred feet from it, and I can't find it then I have no business traveling.

Er, you mean the GPS won't take me right to the doorbell?

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GPSMAP64s, iPhone XR w/Garmin North America, Yaesu VX-8R w/GPS.

Where's the doorbell?

Maybe yours will, mine won't

--
Anytime you have a 50-50 chance of getting something right, there's a 90% probability you'll get it wrong.

In Dash GPS

I have a Kenwood In Dash GPS and driving around SK, AB, and B.C., I have never seen it get tighter than 3 Meters. That is with WAAS enabled and generally 6-8 birds in view. Driving over the mountains, when I get to a summit, I always check the elevation and it generally is out by a couple hundred meters.

Try this

Show track log. Then leave the unit on all night. Next morning when you zoom in, you will see the track had wandered all over the city block.

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1490LMT 1450LMT 295w

NGS Markers

GadgetGuy2008 wrote:

If you want to find out the true accuracy of your gps unit you could go to an NGS marker and compare the known coordinates to the gps coordinates.

There are several diffent kinds of NGS markers and not all of them have coordinates marked on them.

One can determine what markers are in their area and what the coordinates are by looking them using the NGS data sheet Retrival Page here:

http://www.ngs.noaa.gov/cgi-bin/datasheet.prl

If one has already physically found the marker and has the ID number, the marker's full information can be found via the PID method.

If one does not know where a marker is they can list the ones near an area of interest by using the USGS Quad, County, or Map Search methods. Then pull up the data sheet for one or more markers.

Be sure to take note of what Datum applies to the coordinates given on the data sheet for the marker. If it is not the same as one's GPSr uses, conversion will be necessary before comparing location accuracy.

What screen on a nuvi to show satellites

Nuvi1300WTGPS wrote:

My Nuvi 1300 WT ...
It took between 20 to 30 seconds to acquire all 10 satellites. Sats #3,6,13,16,19 & 20 were all above 75%.. while #'s 20,25,30 & 31 were at 100%. It also showed a accuracy of 10 feet.

How do I get my Nuvi 1390T to show me which satellites it has acquired and what it calculates for accuracy?

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-Quest, Nuvi 1390T

satellite constellation screen

To get to the satellite constellation screen, press and hold the satellite strength bars in the upper left corner of the main menu screen.

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Alan - Android Auto, DriveLuxe 50LMTHD, Nuvi 3597LMTHD, Oregon 550T, Nuvi 855, Nuvi 755T, Lowrance Endura Sierra, Bosch Nyon

Thanks

Had tried that but hadn't been holding long enough. Thanks!

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-Quest, Nuvi 1390T