Centimeter-level precision GPS for $900


Via Hackaday:

Where most GPS receivers only look at the data coming from the GPS satellites orbiting overhead, the Piksi uses another technique, real-time kinematics (RTK), to determine the receiver’s location with exacting precision. The basic idea behind RTK is to look at the carrier frequency of the GPS signals at 1575.42 MHz. This frequency has a wavelength of 19 cm, compared to the alternating 1s and 0s of the that are transmitted at around 1 MHz, or about 300 meters between each bit. While centimeter-level precision isn’t possible with only one receiver, two of these Piksi boards – one base station and one on a vehicle, connected via radio link – can make for a very exacting high-accuracy GPS receiver.

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  • Monroe, My guess is your radio sondes read psuedo range and carrier phase, not raw GPS.....

    The remote s/w is managing orbits etc...and solving for position.

    The 4G lockout limit in commercial GPS is not in this part of the code, the 4G limit is inherent in the psuedo range tracking loop. So your radio sonde will most likely not handle any more G's than a normal GPS. So if you are looking for this to solve your rocket GPS problem its likely not going to work.  Niether is the GPS thats the subject of this post. Given that you can probably modify the GPS that is subject of this post to open up the tracking loops sacraficing precision to get a wider G range.....

  • Just wondering? Using the Agixel software and having this in the UAV to georef the photos would that remove the requirements to stitch the photos for NVDI applications? Reason I ask if I don't need to stitch and overlap the photos when capturing the image I can cover a lot more area per hour of flight. just wondering?

  • Yeah I think the application is very interesting..  is 900 for the package or just the receiver?  

    There is quite a few things that I could see this coming in very handy.. since I am working on remote sensing software with my software tool AgPixel.. something that I would like to be able to do is have a receiver like this with a laptop where the end user could use the VI map or any other sort of map they generate in the tool and then use a receiver like this to pinpoint certain things that show up in the imagery or reverse.. use it to pin point issue items and do some sort of supervised classification technique.   Or in the initial setup establishing ground control points to geo reference the imagery... sort of a one time survey of each field.

    Data Collection and Processing Services - AgPixel
    A provider of image processing for use in aerial mapping products and agricultural services.
  • Usage/Application in Ag:  RTK with a fixed base station that never moves gives you both accuracy and precision.  

    Precision=no drift, so when I set my tractor to drive on 120 foot centers while spraying expensive chemicals, it will always have the next pass be 120 feet over, with no overlap or misses.  With normal GPS, depending on the day the signal can drift 6inches to 2 feet.

    Accuracy = repeatablility.  Every time I come to the field, without moving my GPS markers in my tractors computer I will drive on exactly the same tracks, minimizing crop damage.  

    Maybe I mixed Accuracy and Precision up, but you get the idea.  Having a base station that doesn't move during the application (like on a tripod at the flying field) will give you no GPS drift, so you have relative position accuracy (and with 4cm accuracy?!?!?!  yay!)  Having a base station that never ever moves, gives you repeatability over time.  Having a base station that never moves, AND if it has it's actual GPS coordinates hard-coded into it will give you absolute accuracy and precision and happy dreams about flying bunnies!

  • LanMark, you are exactly right, this is VERY exciting for Ag.  Last time we priced out RTK for our tractor fleet the John Deere dealer wanted $18,000 to set up a base station on our farm, and around $10,000 per tractor to set them up with the RTK radios and other hardware (not including the steering valves and computers that are already on the tractors. 

    Our tractors can take like 15 different forms of GPS data inputs, so hopefully without much tinkering we can just feed data from these new boards into the existing autosteering computers.  Build a base station with a powerful transmitter that can cover the whole farm and we'd have RTK for next to nothing.  This is VERY exciting.  Surveying for drainage and other stuff is another application with a small handheld receiver and a base station on a tripod.

    Maybe we'll start up a side business of installing RTK systems for other farms in the area.  Could charge 1/10th of what the dealers charge and still make money.. hmm.. or maybe chard 1/2 or 1/3 of what the dealers charge.. hmm...... :)   Super exciting stuff in any case!

  • Could have interesting agriculture applications since a lot of farms have RTK... Not sure what that means for usage/application
  • Developer

    The problem with carrier phase acquisition is phase jumps. It needs a very fast acquisition rate (100 Hz or more) to avoid phase jumps on a fast moving copters. I'm not sure that RTK can work on a copter with 10 Hz or less acquisition rate.

    Multipathing is a big problem too at the carrier level.

    Before to spend large amount of time trying to make it works, it's important to check that the acquisition rate is fast enough to perform correctly in the difficult copter conditions (fast fly and banking antenna).


  • Moderator

    Did'nt anyone notice we broke this 24 hours early at sUAS News....

  • There ought to be an inter-gps-device RTK correction cloud.

  • As far as I understand the technology, both can be in the air, as long as they have a minimum distance from each other (1m+). Also AFAIU, your don't need 2 receivers for the 50Hz updates but to make RTK possible at all.

    Second, an RTK GPS receiver is able to reduce the ionospheric error with the help of an additional reference receiver. The ionospheric delay varies only slowly with location, so with a nearby reference receiver, the delay is almost the same for both receivers and can largely be cancelled out. This is why an RTK GPS system uses two receivers.


    We are offering two main rewards, the PIKSI and the RTK KIT. The PIKSI is simply a single Piksi receiver for people who only need one receiver. As we explained in our technical section above you need two receivers to do RTK so the PIKSI reward on its own won't allow you to get centimeter level precision.

    From what I have researched, the minimum distance between the 2 receivers should be 1-1,5m. There is e.g. a whole bunch of RTK GPS units for marine applications on the market which simply use 2 or 3 receivers in a huge enclosure with 1-1,5m width.

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