GPS issue...

srose

New Member
Bronze
Jun 10, 2008
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#1
Hi
I have 3G activated right now with full reception. I open google maps and the Blue dot marks my location except it is wrong. I am in the train station and it shows that I am standing on the rails. I went outside but the dot did not move. After a minute it then jumped to a new location because I moved but it showed me across the street.

What Is wrong?

Thanks
 

ron ll

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Jul 13, 2007
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#2
I agree, it doesn't seem to be terribly accurate. If the gps on my boat were this inaccurate, I would have run aground a long time ago. However, it might be that the maps or satelite pictures are not registered accurately rather than a gps problem.
 

Youngbinks

Zealot
Gold
Jun 4, 2007
7,617
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31
Atlanta, Georgia
#5
Sometimes the accuracy isn't 100% and that is just a fact of GPS. Showing you on the tracks means that the GPS is just placing you on the nearest "roadway" or "travelway". Sometimes when I am heading Northbound on the interstate the GPS will show me on the Southbound side traveling in the wrong direction, but it's not like it's that inaccurate.

As far as the DC/GA thing, that's just crazy.
 

nbdiver

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Jul 7, 2008
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Scottsdale, AZ
#6
mine was pretty accurate when I bought my phone a couple weeks back but as of late it has been pretty sluggish along with the rest of the phone. It sometimes won't even zero in on me and other times it has my location about 2 or 3 streets away from where I am. It should be accurate within a hundred to two hundred feet as most normal handheld gps' are!
 

srjeffery

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Jun 4, 2008
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#7
probably depends on where you live. mine actually moves through my house and is dead on.
 

stevetim

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Jul 20, 2007
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#8
The sensitivity/accuracy of the chipset isn't on par with a dedicated GPS, more than likely.
If you are in an area with signal bounce(around tall buildings, metal structures), the line of sight to the satellites diminishes as does the signal's accuracy.

Most dedicated handheld GPS units are accurate to around 3 meters. I don't think they are allowed to consistently be more accurate as the U.S Military had a say about civilian recreational GPS units' ability to do so. The military's accuracy is about 1 meter and better.

The dedicated handhelds themselves take almost a minute to get a locked on signal from about 12 different satellites from a cold start. Meaning, the unit was off, you turned it on, and now about a minute later, you have that 3 meter accuracy. I don't know if the iPhone can read from more than 6 satellites at a time, so it will take longer to lock on, and won't be as accurate, in most cases.

There was a quote from SkyCaddie which is a golf course GPS mapping company. They rely on high accuracy from the units they sell so you can be anywhere on the course and know how far you are from the cup. They declined to produce software on the iPhone because the "GPS chipset in the iPhone isn't as accurate as we like and is intended only for general recreational usage".

I've had periods where the GPS was literally spot-on, and instances where the GPS is about a couple hundred feet off. All with a clear view of the sky.
 

ldivinag

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Jul 29, 2008
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#9
actually, the accuracy of even the commercial GPS units is on par with the military ones.

the thing that causes "errors" is called SELECTIVE AVAILABILITY (SA). prior to may 2000, IIRC, SA caused about +/- 100 meters of errors of a position.

when SA was turned off, my EPE (estimated positional error) on my garmin 12XL went into the low teens, which used to be high 80-100 meters.

now, the cool thing about SA is that it can be turned on ANYTIME and/or ANYWHERE.

i heard stories during the the war in iraq and 'stan that soldiers were using comm grade units, and not their mil-spec ones.

i think the OP's issues is that the GPS signals were being blocked by the buildings (roofs) and i think the MAP app doesn't refresh fast enough.
 

desibhar

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Jul 1, 2008
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#10
My GPS never works good... It never zooms in all the way and drop my pinpoint direction.
 

stevetim

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Jul 20, 2007
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#11
actually, the accuracy of even the commercial GPS units is on par with the military ones.

the thing that causes "errors" is called SELECTIVE AVAILABILITY (SA). prior to may 2000, IIRC, SA caused about +/- 100 meters of errors of a position.

when SA was turned off, my EPE (estimated positional error) on my garmin 12XL went into the low teens, which used to be high 80-100 meters.

now, the cool thing about SA is that it can be turned on ANYTIME and/or ANYWHERE.

i heard stories during the the war in iraq and 'stan that soldiers were using comm grade units, and not their mil-spec ones.

i think the OP's issues is that the GPS signals were being blocked by the buildings (roofs) and i think the MAP app doesn't refresh fast enough.
The military uses P signals which is precision. We, the public us C/A, which is coarse aquisition. Coarse / Acquisition code or C/A, which is freely available to the public, and the restricted Precision code, or P-code.

Google it and you'll learn more about the true accuracies. Gotta run to work so don't have time to get into this subject more.

 

firewire

Member
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Nov 4, 2007
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18
#12
Did nobody here how a tourist group in Utah followed their gps to a cliff? These reports of inaccuracy are not limited to the iPhone's gps.

For the guy that mentioned the train station, are the tracks not right next to the platform? So how far off was it exactly?
 

stevetim

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Jul 20, 2007
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#13
Did nobody here how a tourist group in Utah followed their gps to a cliff? These reports of inaccuracy are not limited to the iPhone's gps.

For the guy that mentioned the train station, are the tracks not right next to the platform? So how far off was it exactly?
The gps itself was fine. Lat/Lon coordinates were accurate. What got them was they were using a "city" unit that didn't have any topographical representation on it.
 

ldivinag

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Jul 29, 2008
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#14
Aug 8, 2008
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#15
from my understanding, the GPS inside of your iPhone is aGPS (assisted GPS). Instead of pinpointing your EXACT location like a dedicated GPS, it merely triangulates your signal from other cell phones, cell towers, wifi hotspots.....etc. That is why you spot is not dead on.
 

alterna

New Member
Aug 1, 2008
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Chicago, IL
#16
i've been having the same issues. it's pretty frustrating.. it's either ridiculously slow at tracking my location, blue dot is not where it's supposed to be, or it doesn't move as i'm moving.

for now i'm just using it to get a general idea of the surrounding streets, not replying too heavily on it. that's what garmin is for. i hope it'll be improved through updates or with better 3G coverage..
 

srose

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Jun 10, 2008
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#17
hi
It seems to be working better now. I was walking down a street and tried it, it was very smooth and showed exactly where I was. Could the train station have interfered? It's always wrong in that station.
 

gibby71

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Jan 8, 2008
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in a galaxy far far away...
#18
I have found that with a reboot of the phone the 1st app you use will get the best GPS reading. I have been using the iPhone for geocaching. I find when I reset my phone and relaunch the phone will put me on the correct spot on the map.
 

mediarite

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Jun 20, 2007
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ColoRADo
#19
probably depends on where you live. mine actually moves through my house and is dead on.
Same here. I've been amazed at its accuracy. Plus it locks on 10 times faster than my Garmin handheld GPS. It's dead on when I'm driving or walking. Appears to be accurate within a couple of feet.

I'm in the Denver metro area. Maybe it has something to do with our elevation.
 
Jun 19, 2007
33,493
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Upper Marlboro, MD
#20
from my understanding, the GPS inside of your iPhone is aGPS (assisted GPS). Instead of pinpointing your EXACT location like a dedicated GPS, it merely triangulates your signal from other cell phones, cell towers, wifi hotspots.....etc. That is why you spot is not dead on.
˜

Assisted GPS helps regular GPS when the GPS signal is blocked or cannot be received well enough to provide a good location lock. aGPS works in addition to GPS on the iPhone 3G:

http://en.wikipedia.org/wiki/AGPS