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Old Jul 24, 2012, 4:09 PM   #1
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Default GPS accuracy.

I use a Panasonic TZ10 (ZS7) that has a built in GPS system. I have found that the accuracy of the system seems to vary in different parts of the world.
I can understand in built up areas that it may get confused but in an open area where the camera tells me it has used 7 satellites to fix the position I would expect the position to be spot on. In practice it is often up to 100 feet out.

For my use this is not really an issue but are all camera GPS systems the same?

If I was trying to moor a boat with this accuracy it could result in a seriously damaged pier and boat.

I have a picture that is tagged about 180 miles out but that was due to the camera not having time to update after being inside a car!
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Old Jul 24, 2012, 4:27 PM   #2
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it depends on the chip set that is use in the gps unit. Some are way more accurate then others.
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Old Jul 24, 2012, 4:42 PM   #3
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Ordinary GPS has an accuracy of from 5 to 15 meters, depending on the chip, antenna, obstructions, and atmospheric conditions. An error of up to 100 feet would be extraordinary if the GPS were the only source of error.
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Old Jul 24, 2012, 4:54 PM   #4
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As mentioned, the chipset used can make a difference. The biggest factor, though is the timebase stability, and this can be affected quite a bit by temperature.
Civilian GPS is not supposed to be accurate to less than ten meters. The system was put in place for military and government use, and these systems can be 'very' accurate indeed. Anybody who is trying to dock a boat or land a plane using GPS is asking for trouble.

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Old Jul 24, 2012, 5:12 PM   #5
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mil grade chipsets are very expensive. We are down in the 3 meter range for accuracy. But high end consumer grade chipsets are getting cheaper. Within 30ft. As the federal government mandated the e911 location info. The cell phones transmit your gps location to the 911 operator. So they have to be within 30ft of you actual locations by law. A camera that cost 250 dollars will not employ a chip set that is as good as your cell phone.
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Old Jul 25, 2012, 7:07 AM   #6
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Quote:
Originally Posted by Talyllyn View Post
I can understand in built up areas that it may get confused but in an open area where the camera tells me it has used 7 satellites to fix the position I would expect the position to be spot on. In practice it is often up to 100 feet out.
Ordinary GPS is not guaranteed to be accurate. Mostly they are accurate to
within a few metres, but errors of hundreds of metres or even thousands of kilometers
are possible under some circumstances. Have a look at some of the websites
where vehicle GPS tracks are plotted on maps. It is not unusual to see tracks
running through fields along the roadside or running through walls and buildings.

Quote:
For my use this is not really an issue but are all camera GPS systems the same?
Yes. Cameras are portable devices with relative slow updates of one fix
per second or longer. GPS is most accurate when the receiver has a static
fix based on the average of a large number of position calculations.

Quote:
If I was trying to moor a boat with this accuracy it could result in a seriously damaged pier and boat.
That could end badly. A small boat could be damaged. A big ship could end
up parked on the street.

Quote:
I have a picture that is tagged about 180 miles out but that was due to the camera not having time to update after being inside a car!
Even greater errors are possible after a cold start.
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Old Jul 25, 2012, 7:12 AM   #7
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How did you figure out that the GPS was off by 100 feet?

What were you comparing it to?
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Old Jul 25, 2012, 3:19 PM   #8
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Quote:
Originally Posted by TCav View Post
How did you figure out that the GPS was off by 100 feet?

What were you comparing it to?
Thank you for the interest in this.

On several picture I know exactly where I was when the picture was taken but when they are plotted on Google Earth they are in the wrong place.
For instance the photo below was taken from the landward end of the walkway to the east of the position shown.

Of course it could be the Google Earth plotting bit that is causing the errors.

Knowing the position to the exact spot is not important to me, the rough position will (I think!) usually be enough to tell me where it is. I have several photos digital and pre-digital where I am now not sure where they were taken due to lack of suitable labelling at the time.

At least with the exif data the date the picture was taken is recorded,assuming the camera is set right. I have an old photo of my mother and her sisters taken around 1935 that says on the back "The bunch of us last week.." so very difficult to date accurately!

Cheers

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Old Jul 25, 2012, 4:00 PM   #9
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Oh, Google Earth. Compared to Google earth, your GPS is a precision instrument. Why this is so, I'm not sure, but my guess is that locations are calculated from satellite data, based on the model of the earth as a sphere. Close enough for most purposes. It appears to lose precision the farther the location is from the Equator, and where local elevations are further from the spherical surface.
My own home would not be seen from where Google Earth thinks it is.

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Old Jul 25, 2012, 4:10 PM   #10
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Actually, Google Earth has my home exactly where my Garmin GPSMAP 60CSx says it is.

In fact, I use it while it's mounted in the center of the dashboard of my car, and Google Earth is pointing to the center of the dashboard of my car, which is parked in my driveway.
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Last edited by TCav; Jul 25, 2012 at 4:24 PM.
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