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Do GPS modules work inside — Parallax Forums

Do GPS modules work inside

whiteoxewhiteoxe Posts: 794
edited 2014-05-04 05:09 in General Discussion
Because my Nav Man needs to be outside or in the car ? I think im having an epiphany... no., just kidding, that's a word i hate because i hear it everyday and it starter about 7 years ago here in oz. If all the people on the tv could just look it up once they would not use it every day :)

Comments

  • whickerwhicker Posts: 749
    edited 2014-04-30 00:19
    the answer in general is: no.

    however, you might find that you can get it to work in a particular building. sometimes. maybe. on certain days.
  • dnalordnalor Posts: 222
    edited 2014-04-30 00:31
    You need visual contact to the satellites. At least to 3 of them. Imagine the signals from the satellites like light. So you have to be (very) near a window if you are inside.
  • Cluso99Cluso99 Posts: 18,069
    edited 2014-04-30 00:51
    GPS will usually work through plastics which include fibreglass (eg on my boat). The aerial has to effectively see the satellite without anything blocking the signal. Metallic structures block the signals or they can reflect the signals (also no good). This is why metal frame buildings often are useless for good wifi coverage.

    In a car, the GPS is seeing out through the front windscreen, not through the roof which is usually metal.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2014-04-30 06:33
    My stock PMB-688 works ('A') throughout the house.
  • Mike GreenMike Green Posts: 23,101
    edited 2014-04-30 07:05
    How much signal the GPS unit sees also depends on whether there are trees in the line-of-sight, how leafy those trees are, the water content of the leaves. In a house, the signal level depends on how much wiring and metallic piping there is in the walls and ceiling / floors above and the spacing between wires / pipes, whether the insulation has aluminum foil as a heat reflective layer, etc. Sometimes there's metal sheathing on the roof ...
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-04-30 14:01
    Some GPS models work pretty well indoors while others need a clear sky. I was amazed at the difference between the first two GPS units I purchased.

    One could get multiple satellite locks while ten feet from the closest closed window in a few seconds and the other had to be outside and stationary for about ten minutes before it could establish a lock.
  • prof_brainoprof_braino Posts: 4,313
    edited 2014-04-30 20:41
    Yeah, I heard the same, trees block the signal because of the water content. So does that mean the lesser GPS unitswill also have trouble on cloudy days? On humid days?

    The units that work inside, it that due to the antenna being more sensative? Can we mod the anttenna on a cheap one to get better performance?
  • xanaduxanadu Posts: 3,347
    edited 2014-04-30 20:59
    You need to define "inside", your current position, time and date.

    The most sensitive GPS I have used are uBlox and whatever is in a G1000 panel mount.
  • xanaduxanadu Posts: 3,347
    edited 2014-04-30 21:23
    Let's take a couple of the many factors into accuracy.

    IMHO - The largest factor is where you are in relation to the GPS satellites. This is entirely disregarding environmental factors, as well as antenna issues. If you have GLONASS you'll have more sats available. Even still those satellites need to be revived in order to be effective.

    The Bad Elf is a popular GPS rx, I'll show you what it looks like inside. This is nothing but a fix, you cannot use it to navigate "inside", so again it depends on specifics. If you just want a fix within a few meters, sure there are lots of GPS that work inside. If you want to navigate around a parking garage then the answer is GPS wasn't designed that way.

    First you need to evaluate where the GPS sats are in the sky, and what you're receiving

    IMG_0010.PNG

    Sometimes, depending on lots of factors you'll pull a good signal inside while you're stationary. That doesn't mean you'd get a good update if you moved. GPS positioning depends on lots of external factors, but most importantly your current fix is an average. Raw GPS data is near incomprehensible, it takes a lot of work to provide a fix. Sometimes this work degrades accuracy, especially when you don't have a clear view of the sky.

    IMG_0011.PNG

    Here's the Bad Elf/GLONASS GPS deep within my compound, about as far as I can get it from a window. 4m of accuracy does me no good compared to what I'd get outside.

    Everything is a factor when it comes to RF data that relies on timing. Sometimes things work well, other times, not so well. Essentially GPS was not made for anything less than a clear view of the entire sky.
  • xanaduxanadu Posts: 3,347
    edited 2014-04-30 21:34
    prof_braino wrote: »
    Yeah, I heard the same, trees block the signal because of the water content. So does that mean the lesser GPS unitswill also have trouble on cloudy days? On humid days?

    The units that work inside, it that due to the antenna being more sensative? Can we mod the anttenna on a cheap one to get better performance?

    You can mod for multipath, there's nothing you can do about weather other than evaluate the availability of what you're receiving.
  • whiteoxewhiteoxe Posts: 794
    edited 2014-05-01 02:06
    it used to blow my mind how the GPS in my car could tell which of the manyh lanes I was in while driving around the city. Felt like it was accurate within a matter of inches. I dont think Ill need a GPS unit on my scribbler unless I want it to patrol the street around me :)
  • JordanCClarkJordanCClark Posts: 198
    edited 2014-05-01 02:26
    Cluso99 wrote: »
    In a car, the GPS is seeing out through the front windscreen, not through the roof which is usually metal.

    Unfortunately there's an exception. We used to have a Pontiac Montana minivan. The radio antenna was a layer inside the entire windscreen.

    On the bright side, radio reception was excellent. On the downside, the GPS couldn't get a read through it. I had to use an external antenna.
  • TorTor Posts: 2,010
    edited 2014-05-04 05:09
    Many modern cars have some kind of metal layer in the windscreen. And thermo windows in houses too. My old GPS receiver (which I got with my TomTom/Palm kit) didn't work inside some cars, and at home I would have to be close to the veranda door - nothing came through the glass in the living room windows. But the glass in the door was different. And I had no reception at all inside the office building, and some problems in cities on streets with near, high buildings.

    All of that changed with the newer chipsets. The old TomTom GPS used a Sirf Star II chipset, the newer Sirf Star III chipset is a completely different world. And the MTK chipset which is used in a tiny bluetooth receiver that I now use with the TomTom navigator. Works inside all cars, has no problems with the living room window, and even works inside most of the office building except when I get deep inside.
    No problems in cities either.

    I don't know what chipset is used inside my Asus Transformer T700T, but that one also seems to work inside many buildings.

    -Tor
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