Is it normal for location to be a bit off?

Yes, this is quite normal. You can't expect a 'phone map app to be as accurate as a dedicated GPS which obtains its info from satellites.

John T said:

Yes, this is quite normal. You can't expect a 'phone map app to be as accurate as a dedicated GPS which obtains its info from satellites.

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Uhm, The GPS in the iPhone also get its info from satellites. The map data is retireved from the itnernet.

That said, it's possible that the map imagery is slightly off, while the actual reported location itself is fine. In any case, yes this happens from time to time, and that's just one of the quirks of GPS vs map imagery.

GPS satellite signal doesn't travel through buildings. It can only obtain when outdoors or very near a window.

Is it possible that your last position outside before entering your house is slightly next door?

corvus32 said:

GPS satellite signal doesn't travel through buildings. It can only obtain when outdoors or very near a window.

Is it possible that your last position outside before entering your house is slightly next door?

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Actually it does. I can get a very accurate location within 10 to 15 feet in my basement, at work, etc.

wxman2003 said:

Actually it does. I can get a very accurate location within 10 to 15 feet in my basement, at work, etc.

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A smartphone can use other means, such as cell towers and wifi, to triangulate its position. These methods work sometimes, other times not so much.

But, to answer the question, it is generally not possible to acquire GPS satellite signal indoors, in dense wooded or urban areas, canyons, etc.

Having wifi on really helps to refine your position especially when indoors and downstairs.

corvus32 said:

But, to answer the question, it is generally not possible to acquire GPS satellite signal indoors

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IMO this is one of the biggest falsehoods perpetuated in the technology world.

Yes, that's certainly the case if you're in a tall building and you're not very high up or where the building has a metallic roof of some sort, but in the average house or smaller office building I never have a problem getting a GPS signal on a smartphone or similar device.

Perhaps it has something to do with differing construction standards and building types around the world...

Daveoc64 said:

IMO this is one of the biggest falsehoods perpetuated in the technology world.

Yes, that's certainly the case if you're in a tall building and you're not very high up or where the building has a metallic roof of some sort, but in the average house or smaller office building I never have a problem getting a GPS signal on a smartphone or similar device.

Perhaps it has something to do with differing construction standards and building types around the world...

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If you have wifi enable, then you'll be fine. I don't have a problem either except for those places you mentioned. I remember though, I had a little Garmin ForeTrex 301 and I was in a guard tower made of thick cement and glass windows. I had to stick my arm out the window in order to acquire a satellite lock. So people are probably confusing that type of behavior with how mobile phones act these days.

Daveoc64 said:

IMO this is one of the biggest falsehoods perpetuated in the technology world.

Yes, that's certainly the case if you're in a tall building and you're not very high up or where the building has a metallic roof of some sort, but in the average house or smaller office building I never have a problem getting a GPS signal on a smartphone or similar device.

Perhaps it has something to do with differing construction standards and building types around the world...

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There is no falsehood. This is the way GPS has always been.

Using my iPhone indoors (with no cell or wifi signal) the GPS Status app reports satellite fix is poor and horizontal accuracy is 165 meters.

Daveoc64 said:

IMO this is one of the biggest falsehoods perpetuated in the technology world.

Yes, that's certainly the case if you're in a tall building and you're not very high up or where the building has a metallic roof of some sort, but in the average house or smaller office building I never have a problem getting a GPS signal on a smartphone or similar device.

Perhaps it has something to do with differing construction standards and building types around the world...

Click to expand...

Nah. Try using a sat nav indoors and not near a window and it will complain about weak/no signal (mine does at least).

Phones usually have A-GPS (the iPhone does), which means they can use cell towers and WiFi to get position too, so when you open up maps indoors it's probably because you're connected to WiFi.

Doesn't civilian GPS have some margin of error?

The military doesn't want you to build your own hell fire drones!


Anywhoo, mine is perfect, it even pin points the exact part of the house am in! Actually that would be bad if I pissed sum1 off.

Where I work there is no wifi, yet gps places me within 10 feet of my location. No cell tower triangulation will ever get me that close. In fact, with my old razr maxx, I could define what to use in finding my location. I would have it only use the satellite, and not cell phone or wifi. It would start out by saying finding satellites, and it did, and would locate me inside that building that had a metal roof and brick sides. So yes, gps works inside buildings.

wxman2003 said:

So yes, gps works inside buildings.

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GPS on phones work inside buildings. Like I said, my Garmin ForeTrex 301 has to be able to see the sky for it to lock onto any Satellites. I'd have to go look at the tech specs on it to see what exact type of technology it uses compared to smart phones.

matttye said:

Phones usually have A-GPS (the iPhone does), which means they can use cell towers and WiFi to get position too, so when you open up maps indoors it's probably because you're connected to WiFi.

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That's not what A-GPS is or does.

corvus32 said:

There is no falsehood. This is the way GPS has always been.

Using my iPhone indoors (with no cell or wifi signal) the GPS Status app reports satellite fix is poor and horizontal accuracy is 165 meters.

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This is what I get indoors

I'm not next to a window and (quite unusually) the roof of the house is also covered in snow.

Perhaps I am getting a GLONASS signal - I don't really know enough about it to say whether it's better indoors or even if iOS lets Apps access the same sort of data from it.

Daveoc64 said:

That's not what A-GPS is or does.

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A-GPS uses cell tower triangulation/network information to find the closest satellite and get a faster lock on, but mobile phones often use other location services in tandem.

Any modern phone that supports A-GPS will support location by network/wifi too.

matttye said:

A-GPS uses cell tower triangulation/network information to find the closest satellite and get a faster lock on, but mobile phones often use other location services in tandem.

Any modern phone that supports A-GPS will support location by network/wifi too.

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That's not A-GPS

https://en.wikipedia.org/wiki/A-GPS

Daveoc64 said:

That's not A-GPS

https://en.wikipedia.org/wiki/A-GPS

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""Standalone" or "autonomous" GPS operation uses radio signals from satellites alone. A-GPS additionally uses network resources to locate and use the satellites in poor signal conditions. In very poor signal conditions, for example in a city, these signals may suffer multipath propagation where signals bounce off buildings, or are weakened by passing through atmospheric conditions, walls, or tree cover. When first turned on in these conditions, some standalone GPS navigation devices may not be able to fix a position due to the fragmentary signal, rendering them unable to function until a clearer signal can be received continuously for a long enough period of time. A fix may take as long as 12.5 minutes (the time needed to download the GPS almanac and ephemeris).[2]

An assisted GPS system can address these problems by using data available from a network. For billing purposes, network providers often count this as a data access, which can cost money depending on the plan.[3]

Assistance falls into two categories:

Information used to acquire satellites more quickly [Mobile Station Based(MSB)]
It can supply orbital data or almanac for the GPS satellites to the GPS receiver, enabling the GPS receiver to lock to the satellites more rapidly in some cases.
The network can provide precise time.
Calculation of position by the server using information from the GPS receiver [Mobile Station Assisted(MSA)]
The device captures a snapshot of the GPS signal, with approximate time, for the server to later process into a position.
The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it.
Accurate, surveyed coordinates for the cell site towers allow better knowledge of local ionospheric conditions and other conditions affecting the GPS signal than the GPS receiver alone, enabling more precise calculation of position."

Pretty much what I said it uses information from cell towers to obtain a better lock on a satellite.

matttye said:

Pretty much what I said it uses information from cell towers to obtain a better lock on a satellite.

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No, it connects to an A-GPS server (i.e. over the internet).

The A-GPS server provides data that makes the GPS lock faster.

The only link to "cell towers" is that your mobile data will obviously run through them.

Theoretically, A-GPS could work with a Wi-Fi or wired connection - but whether it does or not would depend on the type of device you are using.

Daveoc64 said:

No, it connects to an A-GPS server (i.e. over the internet).

The A-GPS server provides data that makes the GPS lock faster.

The only link to "cell towers" is that your mobile data will obviously run through them.

Theoretically, A-GPS could work with a Wi-Fi or wired connection - but whether it does or not would depend on the type of device you are using.

Click to expand...

Fair enough; I was a bit confused about how it works.

However the entire point was that its unlikely that the phone will be using GPS (or A-GPS) indoors to get a location fix, it's more likely to be using wifi and cell tower triangulation; which almost all modern smartphones are capable of doing.

what you all forget is what happens if i move my router

My iPhone always shows my location to be across the street where I live

Sometimes it's accurate though.

Daveoc64 said:

This is what I get indoors

I'm not next to a window and (quite unusually) the roof of the house is also covered in snow.

Perhaps I am getting a GLONASS signal - I don't really know enough about it to say whether it's better indoors or even if iOS lets Apps access the same sort of data from it.

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I see you also have cell signal, and that could be why.

In the attached screenshot, I'm indoors with no service.

corvus32 said:

I see you also have cell signal, and that could be why.

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How?

My cellular provider does not know where I am to 10m accuracy.