Problem about GPS

[bj097]

I have been searching and exploring this issue for long time on the web but I can hardly find any concrete answer. I really wish someone experienced in this area will give me a convincing answer

On Google it's said accuracy of GPS could be up to 2m (20cm) or 3m (30cm) but some said it could be up to 20m or 50m. Some said the GPS could just spot your body exactly. It's really confusing. 2m, 3m and 50m are very different.

I know that GPS on iPhone is improving over years. However, the pictures that I took with my iPhone 4S, iPhone 8 and now iPhone 12 have the same approximated location even if I have turned on the accurate in the location services, and the location is about 50m away from my actual location.

I know that the actual result may vary with surrounding environment e.g. wifi spots, cellular tower, strength of the GPS signal and and even weather, so now.

Given the best condition, theoretically, how accurate could the GPS be ?
Given the usual condition, normally how accurate is the GPS?

I have been seeing a few people saying that it could be just as accurate as exactly where you are standing. Well, what are the apps they are using and how they configure in the setting to achieve this accuracy?

((( You may skip reading this, but I want to say that I need to turn on location services for my camera and take pictures and I will also share these pictures, I do NOT mind my approximated location revealed, but I really mind that if my actual room number of my apartment can be found by location services. )))

 

[wilberforce]

It depends on how many and where the satellites are in relation to you, and they are constantly moving ( not geostationary) plus a number of environmental conditions, plus how many other sources of positioning information, plus availability of positioning correction information.
So the short answer is that the accuracy and precision (which are different things) are constantly varying. It also depends on the equipment - some surveying equipment is accurate to inches/centimeters.
The blue shaded circle around your position in the Find My app, or in google maps or apple maps app indicates roughly the accuracy of your position at any one time. By tracking this over a long time the position can be statistically refined to much greater accuracy

 

[bj097]

It depends on how many and where the satellites are in relation to you, and they are constantly moving ( not geostationary) plus a number of environmental conditions, plus how many other sources of positioning information, plus availability of positioning correction information.
So the short answer is that the accuracy and precision (which are different things) are constantly varying.

then could it spot the actual room number (e.g. height of an apartment) under the normally best condition in reality? I know that it varies, but what is the best accuracy usually

 

[skyhawkmatthew]

As Wilberforce said, GPS accuracy is a function of how many satellites your device's antenna can "see" at a given time, and how well it can see them. With an unobstructed view of the sky in an open area, location error can be less than a metre (e.g. fancy tractors can use GPS to position their runs sowing in a field; airliners can get precisely to the touchdown zone in minimal visibility). In normal conditions on a built-up city street with the phone, I'd expect it to be typically within 50m. Out in an open area, especially given a little time to hone the fix, it can certainly be spot-on.

 

[wilberforce]

Altitude accuracy is usually much less than horizontal accuracy, but this depends on how many satellites are received. Gps signals are not well received indoors so I doubt it could locate the floor you are on

 

[now i see it]

The location tagged onto a photo you take will always be generalized. It’ll never pinpoint exactly where the photo was taken. It’s purpose (location tagging) is primarily used for general use, like the name of a town.

Even hand held dedicated Garmin GPS devices aren’t repeatably accurate to 5 meters. In my experience, I’d give them a pinpoint accuracy of about 40 meters when a place is visited on different days.
Sometimes it’s almost dead on but other times it’s not.

 

[Boyd01]

I've written a GPS web app and have spent awhile looking at this. Accuracy has certainly improved over the years on the iPhone. My general impression is that it's similar to recent Garmin automotive devices, but not their high-end handhelds. Last I checked, the API does not even report accuracy greater than 10 meters, although it may actually do a little better than that.

Altitude accuracy is horrible with GPS - to the point of being basically worthless. There's just no way it could tell what floor of a building you're on, altitude errors are frequently over 100 feet. And it's not likely that the horizontal position is accurate enough either, especially if you're inside a building.

But the GPS system itself is certainly capable of great accuracy, it all depends on what you're willing to spend. For consumer devices (in the ~$100) range, you can get two or three meters in good conditions with a Bluetooth GPS device. I use a Garmin GLO myself and have done some pretty extensive testing which yielded that kind of result.

The nice thing about iOS is that it will automatically use a bluetooth GPS to replace the internal chip if it has been paired to your device. One thing I like about the GLO is that it updates your position 10x per second as opposed to only once per second for the internal GPS (even less than that in practice). There are also other companies that make bluetooth GPS devices in that price rance, such as Bad Elf and Dual.

You can get sub-meter accuracy with a device from Trimble or SXBlue, but those cost thousands of dollars.

 

[bj097]

I've written a GPS web app and have spent awhile looking at this. Accuracy has certainly improved over the years on the iPhone. My general impression is that it's similar to recent Garmin automotive devices, but not their high-end handhelds. Last I checked, the API does not even report accuracy greater than 10 meters, although it may actually do a little better than that.

Altitude accuracy is horrible with GPS - to the point of being basically worthless. There's just no way it could tell what floor of a building you're on, altitude errors are frequently over 100 feet. And it's not likely that the horizontal position is accurate enough either, especially if you're inside a building.

But the GPS system itself is certainly capable of great accuracy, it all depends on what you're willing to spend. For consumer devices (in the ~$100) range, you can get two or three meters in good conditions with a Bluetooth GPS device. I use a Garmin GLO myself and have done some pretty extensive testing which yielded that kind of result.

The nice thing about iOS is that it will automatically use a bluetooth GPS to replace the internal chip if it has been paired to your device. One thing I like about the GLO is that it updates your position 10x per second as opposed to only once per second for the internal GPS (even less than that in practice). There are also other companies that make bluetooth GPS devices in that price rance, such as Bad Elf and Dual.

You can get sub-meter accuracy with a device from Trimble or SXBlue, but those cost thousands of dollars.

I'm talking about GPS on iPhone. I am not worried about military grade GPS or any other standalone GPS device..... but why the location tagged in the picture taken with my iPhone 4S, iPhone 8 and now iPhone 12 is the same approximated accuracy?

I took a lot of pictures at different times and weather with my iPhone 4S and iPhone 8 and now iPhone 12 but they show the same approximated location (the blue spot is 50m from my real location)

 

[wilberforce]

The nice thing about iOS is that it will automatically use a bluetooth GPS to replace the internal chip if it has been paired to your device.

Good to know. I have several GPS loggers for other purposes (like cameras), but not actually tried pairing with iPhone or iPad.

Here is tracking using iPhone/iPad for trail runs on different days. This has heavy tree cover so GPS reception is not great. Gives an idea of horizontal accuracy (see the scale on bottom left). Maybe 25 ft?
I agree, altitude is not accurate. But elevation gain/loss is not too bad.

 

[Boyd01]

Bluetooth GPS devices and dataloggers are two different things. Check the documentation for your device, I would not assume that a logger is capable of sending position data to your phone unless that's a feature they specifically mention.

 

[bj097]

Hi all above. I am going to read your replies in details, but in the meanwhile, can I just safely assume that pictures taken by my iPhone will not tag or reveal my precise room number? You can assume that I'm living in a well developed country and landmark of the country so there are so many WiFi around and cellular network is very well built, managed and operated. Cellular speed is awesome. From the properties of the pictures it shows only the approximated address, but I am not sure, because I am not playing with computer or mobile system things very well

 

[skyhawkmatthew]

Yes, I would safely assume that your precise room number will not be deducible from iPhone geotags. If you are still concerned, you can disable Camera access to location data in Settings > Privacy > Location Services > Camera.

In that menu, there is an option to allow Camera to use or not your "precise location" – no idea what the parameters are on that, but switching that off may give you peace of mind.

 

[bj097]

Yes, I would safely assume that your precise room number will not be deducible from iPhone geotags. If you are still concerned, you can disable Camera access to location data in Settings > Privacy > Location Services > Camera.

In that menu, there is an option to allow Camera to use or not your "precise location" – no idea what the parameters are on that, but switching that off may give you peace of mind.

I need to use location services for camera so I asked this question. However, I do not want my precise room number be revealed under any circumstances.