Discussions

Sub meter accuracy for the Arducopter GPS?

Posted by Gerard Lavoie on October 5, 2010 at 7:47pm
I am wondering if there is a proprietary binary code output from the compatible Arduino GPS chips, or if an NMEA output is fine?  This is because I want this magical GPS unit onboard: http://www.sxbluegps.com/sxblue-gps.html

Has anybody got a good felling about this sub meter accuracy gps.... it's pricey...  Is it a waste?

I figure it could help with keeping a stable waypoint fix.

G. 

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Replies

  • Developer
    Jani Hirvinen October 6, 2010 at 8:45am
    Gerard, Current hardware does not support SD cards but yes it is possible to record data to onboard "blackbox" due we have memory chip already installed and this data can be extracted later to ground station or other computer via serial interface.

    On ArduPilot Mega code (for airplanes) we now have nice command line interface (CLI) to control logfiles etc many other functions. These same features will be available on ArduCopter. It just takes awhile untill we can start adding more fancy features on ArduCopter. Also with rather small modifications even current code can start control camera gimbal and other camera mounts that can compensate tilt/pan/yaw movements.

    Even logging time can be done to memory. It's just matter of programming issues what to log and how to use gyro outputs :)
    Compensating those movements are done by onboard gyros and because we use gyro output already, it will be really easy to use their output for other things too.
  • Developer
    Jani Hirvinen October 6, 2010 at 7:14am
    Gerard, also what are you trying to achieve with this sub meter accuracy? General accuracy also varies a lot on different areas. If you plan to have position hold for quad less than 1 meter on X/Y plane.. Hmm i'm afraid that it's more or less impossible to have it in real life especially if there are wind. Hold on 3-5 meters is more like possible to achieve. Yes if wind conditions and everything are perfect it is possible to hold quad almost still but only in optimal conditions.

    I personally don't see any real reasons to get that expensive GPS. If you want to have higher update rate than what MTEK provides, I've just tested new uBlox LEAH 6 chips and we got really good update rates and accuracy with that. Downside is that those new GPSes are not our yet so it will take awhile untill we have them.

    It you let us know a bit more about your application, maybe we can point towards right direction.
  • Patrick Hammer October 6, 2010 at 5:05am
    Gerard

    If you read the notes at the end of all the marketing blurb - and it becomes clear that the sub-meter accuracy referred to is subject to certain conditions - as it is with most modern day GPS modules with half decent firmware and onboard filter config i.e. it is capable of sub-meter accuracy, not that you will get sub-meter. accuracy. GPS accuracy can only ever be as accurate as the L/L2 downlink timings are - and they are subject to all the usual multi-path problems that stem from the condition of the atmosphere they have to travel through

    Notes
    1. SVs > 5, HDOP < 2, short baseline from reference station, and low multipath environment.
    2. Dependant upon ionospheric activity and multipath

    Add RTK and now you can achieve sub-1" accuracy and sub-2" repeatibility! (95% of the time - the rest of the time it will drift a couple inch either way) - ask any John Deere tractor driver who has StarFire/RTK GPS system on his tractor.
  • Gerard Lavoie October 5, 2010 at 8:19pm
    http://www.visualgps.net/WhitePapers/NMEAParser/NMEA%20Parser%20Des...
  • Gerard Lavoie October 5, 2010 at 8:16pm
    I think you should send me a sample of the current output log, using Windows Hyper-terminal. It would be a start. I think that reading a standard NMEA output (>1Hz) is a good idea here, if it isn't already the case. I should look at the log, and compare it to the SXBlue output... if they are strung differently, that is an easy fix.

    G.
  • 3D Robotics
    Chris Anderson October 5, 2010 at 8:07pm
    We have a NMEA parser but it doesn't work very well. It's all open source, however, so if you can improve the code everyone would thank you!
  • Gerard Lavoie October 5, 2010 at 7:50pm
    I found out that Mikrokopter has locked out anything but their 3-5 meter accuracy MKGPS chip... that killed it for me. I just jumped ship. :) I'm glad I haven't spent any money yet :)

    The GPS fix is a big one for me....
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