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Thread: Why GPS without inertial navigation fails.

  1. #11
    ptk is offline
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    Apr 2004
    this has been discussed before.
    all in all, if you navigate mostly around low build up area, conventional GPS is suffice for you.

    however, if you navigate around high rise build up area (i am, i live in singapore), GPS signal drop out is a major issue.

    Dead reckoning (GPS coupled with gyro + vehicle speed input) offers ideal solution. however, they don't come cheap.

    alot of the OEM kit for high end cars use this system

    commercially available kits are hard to come by.
    here's a few company that offers it
    1. Whitebream claims to be developing one
    2. uBlox
    3. Trimble
    4. Point Research

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  2. #12
    Low Bitrate vision's Avatar
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    May 2004
    NY, USA
    Actual teme for ppl who driving alote in city with high buildings

  3. #13
    Low Bitrate BeamRider's Avatar
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    Apr 2004
    Genova, I
    The real issue is "why inertial navigation fails without GPS"

    Inertial system are far less accurate and hard to use than GPS:
    - you need to know your coordinates when the system starts
    - you need to keep position while it initialise (some minutes in aircraft systems)
    - you need to refix due to gyro drift (that's why they use GPS to correct position errors)

    The good in INS is that they are a lot faster in response than GPS but we don't really need this kind of systems in our car.
    What Pioneer and some others uses is a compass to correct the heading information from GPS when you're not moving or moving very slowly (an inertial system is far more complex!). When you loose GPS signal the navigator uses your last known speed and current heading to assume your current position.
    This is absolutely feasable with our carputers: it's matter of finding a compass (similar to and write a small application to correct GPS messages.

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  4. #14
    Maximum Bitrate
    Join Date
    Jun 2000
    I never have an issue with being off the road.

    Hardware - the Ebay GPS mouse (WAAS enabled)
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  5. #15
    Jesus Freak antimatter's Avatar
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    Jan 2004
    So even if i did buy one of these "commercial Gyro/GPS systems" could i use the current software (iGuidance2)? or would i have to use a special software that accepted the other data? I would assume that the software would have to support differential positioning before you could utilize it
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  6. #16
    Confusion Master
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    Enforcer's Avatar
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    Sep 2003
    If you go down to the woods today, You're sure of
    Quote Originally Posted by Laidback
    And some software has the 'snap to road' feature, which keeps you on the road as well. I find mine pretty accurate!

    except when it decides you took the turning off the motorway junction when you didn't (or vice versa)

  7. #17
    Variable Bitrate Curly_cat's Avatar
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    Jun 2004
    Ipswich, UK
    The conspiracy theories of non accurate GPS co-ordinates rear their head yet again!!

    I only find that I'm off the map when I take the bypass that hasn't been added yet. Always meet the road again soon though.

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  8. #18
    Constant Bitrate ccblanket's Avatar
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    Sep 2003
    SF Bay Area
    in norcal locations are always perfectly matching onto the maps on my computer. exceptions are recently added/removed exits, etc. technically the position could be a few feet off but hey I need driving directions not instructions to locate a pin. cost/benefit is not worth for me to buy a nav w/ gyro. ymmv.

  9. #19
    cheap custom title JC-S60's Avatar
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    Mar 2004
    Ghent - Belgium
    As said before, the real problems start when you loose your gps signals. There are a lot of occasions: tunnels, woods and certainly cities with a lot of high buildings (where navigation could certainly prove it's point!).

    Also, when I had my VDO system, I liked the fact that I could see the direction I was headed to on the map, even when standing still.

    @antimatter: I think these systems simulate a very accurate GPS by sending modified/recalculated NMEA data to the serial port, so your existing software would still work, even with bad/no gps reception.

  10. #20
    Raw Wave rando's Avatar
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    Mar 2004
    Redondo Beach, CA
    @Antimatter, the device I've been using to test our I2C code for Seth's radio project is the CMPS03 compass (mentioned a few posts back). You can get it for around $50. I plan to do exactly what JC-S60 just said and integrate this data with my GPS data stream and then output a new NMEA stream. The software doesn't need to know about it.

    I already have my GPS reader code and have built a small circuit to sample my speed sensor over the serial port (note: this can probably be done a bit more accurately with a small MCU). I still need to do some in-car testing on both devices to better understand their limitations. After that I'll do the integration and then I'll try it out with Mappoing and Street Atlass -- but it should work with anything.

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