External vision ekf2 timeout and reset

[tuloski]

Hi all.
I'm testing external vision for altitude on gazebo simulator.
I'm using:

• EKF2_HGT_MODE vision
• EKF2_EV_DELAY 100
• I'm sending the EV mavlink message including ONLY timestamp and z field @20hz

but I get a few "EKF ev hgt timeout - reset to ev hgt" and suddenly the altitude have a jump and the quadrotor moves up or down.

My questions are:

• Do I need to sync the timestamp of the external vision with the IMU? If yes with which precision?
• Is EKF2_EV_DELAY the delay w.r.t. IMU data or w.r.t. the reality?
• Can the "EKF ev hgt timeout" be only a simulator error due to poor hardware to simulate (the simulation on gazebo is running realtime @50Hz so it shouldn't be a big problem).
• Why if I send the data @20hz, on the log the vision data is only @4hz? Is there a maximum rate? See the attached log.
• Why the local position estimation seems to lag for a few seconds as if didn't have any data? See attached log. Probably related to "EKF timeout" problem.

Attached log: https://review.px4.io/plot_app?log=d9e21090-1c02-48d5-9b62-0781e04c77bf

[TSC21]

This happens because EKF2 expects you to send the full position vector (XYZ), not only one of the dimensions - https://github.com/PX4/Firmware/blob/master/src/modules/ekf2/ekf2_main.cpp#L1203.

[tuloski]

@TSC21 are you sure? Because otherwise why does it work for a while, and tracks the altitude I send as vision estimate? And why is there "EKF2_HGT_MODE vision" that I can enable only for height?
I didn't put the flag to use complete vision for position estimation in EKF2_AID_MASK, but only EKF2_HGT_MODE.

BTW I send the full vision_estimate message, but the other fields are 0.

[TSC21]

@TSC21 are you sure? Because otherwise why does it work for a while, and tracks the altitude I send as vision estimate?

Yes I am sure. It tracks it because the other fields are 0 but are numbers.

And why is there "EKF2_HGT_MODE vision" that I can enable only for height?

It basically says that the estimator relies on the vision input only. But it doesn't mean you don't need the full vector.

[tuloski]

Right. Thanks.
So there is no way to feed only the altitude from an external module, if not modifying the code.

[tuloski]

BTW the documentation says:
"External Vision System
Position and Pose Measurements from an external vision system, e.g. Vicon, can be used:

External vision system horizontal position data will be used if bit position 3 in the EKF2_AID_MASK parameter is true.
External vision system vertical position data will be used if the EKF2_HGT_MODE parameter is set to 3.
External vision system pose data will be used for yaw estimation if bit position 4 in the EKF2_AID_MASK parameter is true."

So either the doc is wrong or there is another issue here.

[tuloski]

Can someone point me at the code which triggers "EKF ev hgt timeout - reset to ev hgt"?

[TSC21]

https://github.com/PX4/ecl/blob/master/EKF/control.cpp#L914

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

Closing as stale.

[kashishdhal]

Hello @tuloski,

I am having similar issue. You said it worked for a bit and EKF2 resets to zero. Were you able to resolve it? If yes, can you share?
My problem is mentioned in detail here:
https://discuss.px4.io/t/error-in-local-positioning-of-pixhawk4-using-vicon-data/16011/35