I've read through a few discussions on this forum about poor man's DGPS and getting relative accuracy down to the ~1m range.  It seems no one's having much luck even with identical GPS units.  I'm wondering if anyone has manged this and what are your thoughts on what I'm currently building.

 

I'm laying out a PCB for a ublox LEA-6T (that's the one that outputs raw data and carrier phase) to interface to a MCU and a 433MHz radio.  That's the mobile unit.  My base station is then a single board computer with it's own LEA-6T, radio, and software running GPSTk post-processing software.  The mobile board will then radio the raw data (subframes 1 and 2 and psuedo range and carrier info) to my base station.  Base station code then chooses a set of sattellites that work well for both units and calculates position of both units using the same satallites and same ephemeris data.  (calculated position could then be radioed back to mobile unit)

 

The units are genearlly pretty close to each other (spatially) so the only error here should be that inherent to the ublox measuring psuedorange--no constellation, algorithm, iono/troposphere, ephemeris differences.

 

Has anybody tried this?  Do you think I can get a relative accuracy of ~1m?

 

 

Thanks for any thoughts guys and gals!

 

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Replies

  • Hi, I can suggest you to try DGPS using differential code correction. You can use your own base or grab NTRIP stream from a local GNSS reference. Then, you wireless send RTCM 2.3 correction to any new generation u-blox/NVS receiver.

    We did it. We send RTCM 2.3 correction to a GNSS inside football players shinguard. Accuracy is submetric.

     

    • That's awesome accuracy. Where is your antenna? in the shinguard? ceramic patch?

      • Hi Noland. Yes, we use a tuned ceramic patch inside the shinguard and we wireless send real time corrections. Code corrections are very stable also in dynamic. Accuracy decreases with the distance from the reference (better <10km, best <1km).

  • are there still people following this thread?

    i am setting up my RTK system using 2 ublox receivers and 2 ublox active patch antenna and RTKLIB,,, sometimes i get FIX solution for short period of time but mostly FLOAT SOLUTION. Also, when i get a new FIX the position changes there is no precise point in every FIX.

    can you help me sort things out.

    thank you very much

    PS. here are my config files for ucenter and rtklib


    RTK config.conf

    RAW 10HZ.txt

  • Developer

    Did you ever get anywhere with this?

  • Dear Noland.

    I hope you have it up and running as your question was posted in 2010 .

    I have an u-blox LEA-4T.

    By hardware ublox can only accept input of RTCM messages 1,2,3 and 9. Code messages.

    It would be possible to get centimeter with carrier phase messages 18/20 and 19/21.

    I have reached 1 cm static for a 11km  baseline, confirmed with a L1+L2 geodetic receiver.

    take a look in www.rtklib.com It is a nice GPL2 software.

    I am looking for an RTCM-104 encoder to use 4T as RTK-base.

    regards,

    julio menezes

    RTKLIB: An Open Source Program Package for GNSS Positioning
  • Hi All!

     

    I am also working on a project with the ublox LEA-4T dev kits and RTKLib.  I tried a while ago to get an RTK solution using RTKLib but the quality was quite poor, as the solution drifted by at least 10m to 20m.  This was a static test using two antenna's supplied with the ublox recievers (http://www.u-blox.com/en/gps-antennas/gps-antennas/ann-ms.html), mounted on tripods about 2m apart in an empty parking lot (reasonable sky view, I would say). Does anyone have any advice as to how to improve this solution?  Perhaps better antennas?  What are some good (reasonably priced) options?  I do intend to have them on some flying vehicles eventually, so the smaller the better!

     

    Thanks!

  • Looks like there is also a SkyTraq USB dongle available from a 3rd party:
    http://www.onetalent-gnss.com/products/usb-hw-receivers/yuan10

    Simon
  • If you are having trouble finding/budgeting the Ublox, don't forget that the Skytraq is available with a 'RAW capable' firmware and works with RTK Lib.

    They are happy to take paypal.
    Simon.
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