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Improving GPS accuracy

Posted by ionut on February 12, 2012 at 1:00pm

Real-Time-Kinematic-picture.jpg

It seems there are methods to increase accuracy of the GPS location to cm using a reference station network.

Real Time Kinematic (RTK) satellite navigation  is a technique used in land survey and in hydrographic survey based on the use of carrier phase measurements of the GPS, GLONASS and/or Galileo signals where a single reference station provides the real-time corrections, providing up to centimetre-level accuracy. When referring to GPS in particular, the system is also commonly referred to as Carrier-Phase Enhancement, CPGPS.

Check this link:

http://en.wikipedia.org/wiki/Real_Time_Kinematic

Real-Time-Kinematic-image.jpg

Tags: accuracy, gps
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Comments

  • Arnaldo Santos October 13, 2014 at 9:48am

    Is there a easy way? Like post processing the ardupilot log gps data with the static gps module file recorded by rtklib at the same time of the flight

  • Arnaldo Santos October 3, 2014 at 5:40am

    Did anyone figure out how to convert the UAV gps data to use on RTKLIB? 

  • MarcS February 13, 2012 at 1:50pm

    Simon, you should separate RTK and RTKlib, otherwise we will end in confusion here :-) RTK receivers work in pairs without additional PC for the processing... (Thats what Wolfgang called base station mode..)

    Wolfgang, are you talking about the RTK L1/L2 mode of the Eclipse II? I would expect better results from high grade components like these...

    My personal experience with commercial RTK is much better, 2cm at 20Hz with high dynamic rover receiver (Plane)...

  • Simon Wood February 13, 2012 at 12:50pm

    For RTK to work you will need (at least) 1 way data channel for corrections, and a processor (PC?) to perform calculations. The library is straight C, so could run directly on a processor of your choice (given enough MIPS).

    Correction data can be sent as RTCM which is low bandwidth/compressed. RTK can work OK with a reasonable latency (say 5s).

    All uBlox receivers support serial (RS232) as well as USB, so this can be hooked directly to a wireless modem/cell/zigbee or other radio (ie. without the need for a PC at that part of the system).

    Will this work for you? Depends on what you are trying to achieve....

  • ionut February 13, 2012 at 12:20pm

    Colin-Great, but how are the base and rover going to communicate to each other.Rtklib is a Linux or Windows library, therefor you will need at least 2 computers and 2 usb connected uBlox receivers to have a minimal test platform.Also you will need some kind of wireless communication between these 2 computers.Right?

  • MarcS February 13, 2012 at 12:20pm

    Did anybody try rtklib on a plane/Copter? Whats the accuracy? Does it work in high dynamics?

    I think all solutions apart from "real RTK" using L1/L2 will provide resolution in the meter domain, especially in altitude... Which means for the part of flight where high accuracy is needed, the landing (or other stunts close to the ground :-), it´s still not good enough.

    So for me there are two options: I got the money and buy RTK or I look for alternatives like optical, sonar, radar etc...

  • ionut February 13, 2012 at 11:52am

    Simon, I don't think that library rtklib will work with cheap GPS receivers like uBlox.It will work only with the survey ones.Maybe Dave is closer to a practical DIY solution with DGPS.

  • Simon Wood February 13, 2012 at 10:01am

    It's been mentioned here before several times.....

    http://www.rtklib.com

    Just add a couple of (cheapish) uBlox and SkyTraq receivers, or if your budget stretches to it a survey grade receiver such as Trimble, Novatel or TopCon you can get better performance. If you're really cheap some Garmin receivers can output raw data.

    RTKLIB: An Open Source Program Package for GNSS Positioning
  • SaadT February 13, 2012 at 5:32am

    The one you've mentioned requires special antenna and GPS receivers (those that are capable of tracking phase as well), which are more expensive (and heavier). 
    A better, lower cost option, in my opinion is Differential GPS (known as DGPS). It uses normal antenna, normal GPS receivers...only RTCM corrections are sent from the base to the mobile units over a data link. This gives accuracy of within a meter, which is reasonable in many situations. This is from my knowledge working as a seismic engineer,..we use both RTK and DGPS out here on the field.
    I'm myself thinking of implementing a DGPS scheme myself. Basically i'll fix my base station and then generate and send corrections to the mobile unit. One problem here is that either i know my base station position very accurately OR i keep all positions relative. Lets see how it works.

  • Lyn Rees February 13, 2012 at 4:23am

    I think Gary is thinking about OS NET. This is as he said a service offered, at a price of course, by OS in the UK

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