GPS Altitude?

Posted by Michael Doornbos on January 22, 2016 at 1:18pm

I'm not ready to abandon my Iris+ yet because it's still useful, but the detected altitude (and other GPS numbers) change constantly when it's sitting on a table.

I have a bluetooth Garmin GLO that I use in actual airplanes that I put on the same table and connected to Foreflight. It sits steady at 736 meters.

The Iris Fluctuates between 735 and 750 meters while sitting on the table. The position moves around laterally, probably 5-10 meters. Again, the Garmin glow shows speed as zero 

HDOP is 1.7 with 9-13 satellites. 

Is there a replacement GPS unit that people have had success with? Maybe with an external antenna?

You need to be a member of diydrones to add comments!

Join diydrones

Email me when people reply –
Follow

Replies

  • Michael January 22, 2016 at 1:55pm

    This isn't exactly an apples to apples comparison here.  There are a lot of factors that go into the data you're reading in Foreflight and what devices are actually doing with that data.  For starters, here are a few points:

    • Foreflight and GLO are design for pilots to use in aircraft that physically exist on a larger scale.  UAVs like the Iris can make small movements in any direction.  This has a large impact of the type and quality of the data your device is transmitting or expecting to receive.
    • The GLO probably wasn't designed to deliver a raw GPS solution to the host device, the Iris GPS was.  Likewise,  Foreflight is probably not expecting a raw GPS solution.  In a UAV, the GPS is not usually the sole source of the altitude solution.  The Pixhawk will use information gathered from other sensors like a barometer and/or the accelerometers to figure out where it is.
    • The GLO may use Kalman filtering or another method for provided better position accuracy or reducing positions/altitude drift over time.
    • GPS altitude accuracy is notorious for being poor, especially with the $100-range receivers and certainly indoors.  Keep in mind that just because the GPS altitude readouts aren't moving doesn't mean that the solution is more accurate.

    Hope this helps.

    • Michael Doornbos > Michael January 22, 2016 at 2:09pm

      And I know that at least at a high level. I was really just using it as a sanity check.

      Bottom line is that the position numbers in my Iris are currently inaccurate enough to be very dangerous. 

      Thanks for your explanation!

    • Michael Burmeister > Michael Doornbos January 22, 2016 at 5:44pm

      I have flown my IRIS for over a year now and have relied on the GPS in many instances without fail.  In the open out doors it Is rock solid for me.  If you get close to a building or in a building forget it.  GPS was not designed to work indoors no mater who makes it.  Doppler effect due to building materials will mess with the reception.

    • Steve Foster > Michael Doornbos January 22, 2016 at 2:40pm

      I think the one that comes with the Iris+ is a NEO7. I replaced mine with a NEO-M8N on a mast, and did notice a pretty big difference. So much so, that I've ordered more NEO8's for my other rigs.

      http://www.amazon.com/gp/product/B00WMDRISA?psc=1&redirect=true...

  • Justin H. January 22, 2016 at 1:47pm

    External compass/GPS antenna with the standard 3DR ublox was the 2nd-best mod I've done to the Iris+, the 10" CF props being first by a hair. It doesn't help with the barometer obviously, but GPS lock was quicker, HDOP improved, the "seeking" behavior you describe dropped by 90%, and performance in trees and canyons improved a lot. The compass was also much happier outside the shell and away from interference. It's very easy to add the external as a secondary GPS, essentially using the internal as a back-up in case the external fails.

    • Michael Doornbos > Justin H. January 22, 2016 at 2:17pm

      Looks like the Mast is no longer available, I'll have to make one I guess.

    • Michael Doornbos > Justin H. January 22, 2016 at 2:10pm

      Any chance you wrote instructions on what you did?

This reply was deleted.