How good are modern GPS receivers indoors?

[bitchstewie]

I'm looking at something which requires a GPS receiver to operate.

I thought the receiver would have to be either outside or within direct line of sight of the sky to be able to "lock" onto a GPS signal.

I thought I'd do a poor mans test by downloading a GPS signal app for my smartphone, which I did, and I'm a little surprised that I seem to be getting a clear signal in places where there simply is no line of sight of the outdoors.

We're not talking anywhere exotic, places such as the airing cupboard and under the stairs and places around the house there there is simply walls on all sides.

I'm probably being a bit of a plank but if the thing cannot "see" the sky how the hell is it picking anything up or is it simply that the receivers are way more sensitive than I may have expected?

[fatandwheezing]

Multipath of the signal mostly. Consumer GPS devices use high gain chips that track very low signal levels, no matter how many walls they've bounced off. It just isn't likely to be very accurate.

Buy a precision high grade RTK receiver and you'll need a good sky view to get a position as they have a higher limit on the quality of signal they use.

Which one you choose depends on the accuracy you need for the job.

[pherlopolus]

They are radio waves so lack of LOS just degrades rather than completely losing the signal. Can depend on the receiver though, my thl 5000 is a bit rubbish, Huawei tablet is much better.

[Beati Dogu]

I have an old Garmin single channel receiver and that is unlikely to get a signal indoors at all. Apparently heavy foliage like a jungle used to be a bit of a problem as well.

The GPS satellite system is complete now, so coverage is also much better than it was when I first got mine. You only need to pick up 3 satellites for a position fix and 4 to give you your altitude.

[droopsnoot]

There was a thing called a re-radiating antenna, we used to use them to bring the GPS signal inside a old A8 that had bronze-laminated windows. Not sure whether that would help, and I'm not sure what position it provides - presumably the position of the antenna rather than the receiver. That wasn't an issue as it was very close in our usage.

[FurtiveFreddy]

droopsnoot said:

There was a thing called a re-radiating antenna, we used to use them to bring the GPS signal inside a old A8 that had bronze-laminated windows. Not sure whether that would help, and I'm not sure what position it provides - presumably the position of the antenna rather than the receiver. That wasn't an issue as it was very close in our usage.

They don't work particularly well in my experience and as for accuracy, you'll be lucky to get sub 2 metre accuracy with most consumer GPS devices.

There are some very expensive trackers out there which are capable of getting an accurate fix with minimal signal. The sort of thing that would allow you to find a car hidden in a shipping container.

If you use a low cost GPS module indoors, you can get reasonable accuracy, but you can also get a lot of spurious data which will look like the receiver suddenly jumping to a position several metres away. Software filtering can help with this, but there's no guarantee it will solve the problem completely.

[anonymous-user]

bhstewie said:

I'm looking at something which requires a GPS receiver to operate.

I thought the receiver would have to be either outside or within direct line of sight of the sky to be able to "lock" onto a GPS signal.

I thought I'd do a poor mans test by downloading a GPS signal app for my smartphone, which I did, and I'm a little surprised that I seem to be getting a clear signal in places where there simply is no line of sight of the outdoors.

We're not talking anywhere exotic, places such as the airing cupboard and under the stairs and places around the house there there is simply walls on all sides.

I'm probably being a bit of a plank but if the thing cannot "see" the sky how the hell is it picking anything up or is it simply that the receivers are way more sensitive than I may have expected?

Aren't most of these apps using stuff like phone signal and wifi hubs etc to assist the GPS? You usually won't get a pure GPS signal indoors unless you're in a conservatory or have a glass roof or the device is on a window sill. Even then it's unlikely to be very accurate.

[bitchstewie]

My phone is surprisingly decent with location turned on and using a 100% GPS based "tester" app.

Seems I'll be shoving the thing I'm looking at on a window ledge as I simply cannot get a signal of any kind where I would like it.

[Zad]

What does it require the GPS for? It may be that it uses it for access to an accurate clock, which has much lower demands on signal strength and signal precision than location. An airing cupboard would just have a layer of plasterboard ceiling and relatively thin tiles above it, which still allow some signal to pass through.

[bitchstewie]

Zad said:

What does it require the GPS for? It may be that it uses it for access to an accurate clock, which has much lower demands on signal strength and signal precision than location. An airing cupboard would just have a layer of plasterboard ceiling and relatively thin tiles above it, which still allow some signal to pass through.

Clock yes so I think it's simply down to whether there's enough of a signal and my airing cupboard must simply have thinner walls than our office.