GPS accuracy decreasing without corresponding decrease in DOP or number of satellites

ArduCopter Copter 4.2
1

I have a companion computer onboard a Pixhawk drone performing a mission of:

  • store current location on companion as home location
  • takeoff to 6m altitude
  • setting position target about 30m away
  • setting position target to return to 14m above the home location
  • once reached a USB camera is turned on to assist landing
  • set position target of 6m above home location repeatedly
  • once 6m altitude reached, perform landing

Sometimes the drone flies back to a location that is over 7m horizontally away from the expected home location yet the logs do not indicate this and in the last 3 steps above, Arducopter thinks it is directly above the home location as requested (<0.2m difference).

It seems I have a GPS issue, so I examined the log of a typical flight (available here).

HDop, HAcc and NSats look good for the entire flight:

all_1637
all_16371543Ă—487 13.7 KB

As mentioned, once landed Arducopter reports that the takeoff location is identical to the landing location. Anyone know if the information I am logging is trustworthy? I was hoping to see much more significant GPS problems in the log.

Thanks!

2

The information that you are logging comes directly from the GPS module. The arducopter firmware does to change it in any way.
So I guess you should complain to the manufacturer that the horizontal accuracy values are 7 times smaller than reality.

1 Like
3

Is there a parameter that describes the difference between what the accelerometers think velocity is, and what the GPS thinks? (It must be clear I have no idea how Arducopter determines velocity!)

I see NTUN includes a parameter that is “Actual accelerometer + gps velocity estimate” which is vaguely the sort of thing.