Preflight: GPS horizontal pos error too high - work arounds and impacts on surveys

[Ben_in_the_woods]

[14:25:59.440] Warning Preflight: GPS horizontal pos error too high

Are there any simple work arounds for this situation?

I undertook a few small surveys after this message popped up during the set up and then went away - the result using WebODM (without GCP's) was that 50% of the images were rejected during the processing. I am assuming that this is because the GPS accuracy was filtered and found not to be good enough???

Are there any fixes or procedures to prevent this? Perhaps hovering higher in the sky (120m) to gain better satellite HDOP fixes? Perhaps compass calibration?

Not knowing whether the photos are going to meet the quality filter until after the mission is a problem for me as it often requires a re-fly.

Any tips or advice would be greatly appreciated.

cheers
Ben

 

[Rayray]

I don't think that pre-flight message is the problem. Annoying as it is, just ignore it and it will go away. Click on the craft icon and watch the number of GPS sats reported. Wait until 12 or more, 14-16 better, before you start your work flight. Try this and see if you have better results. Good luck.

 

[J Walesewicz]

Ben,
What set up of WebODM are you using? The original web based/Docker set up or the newer WebODM Lighting? I use them both and it sounds to me that it is a little more likely the issue is coming from the way the camera is set up in he system. What camera are you using? I use an E90 on my standard H520. I normally fly at multiple altitudes and multiple camera angles before I send the pictures through the program.

WebODM is a fantastic program to use but it does take some time to learn. If you get a chance, try to find a copy of a book written by Piero Toffanin (one of the developers) called Open Drone Map: the Missing guide.

Have fun.

J. Walesewicz

 

[h-elsner]

I don't think that pre-flight message is the problem. Annoying as it is, just ignore it and it will go away. Click on the craft icon and watch the number of GPS sats reported. Wait until 12 or more, 14-16 better, before you start your work flight. Try this and see if you have better results. Good luck.

This is a dangerous assertion that I cannot let go unchallenged.

"Warning Preflight: GPS horizontal pos error too high" means what it say. There is no GPS lock yet and possibly no homepoint set. It needs the whole log file to check this. The number sats in use do not say anything about the GPS lock. The probability to get it faster is higher than more sats are in use but not more.
GPS accuracy depends on some external influences. One of the most common is multi-path receivement.

Multipath | GEOG 862: GPS and GNSS for Geospatial Professionals

The TLOG files from ST16 contains also vertical and horizontale accuracy of the GPS and the GPS fix type. This may help to check what happens.

br HE

 

[chascoadmin]

[14:25:59.440] Warning Preflight: GPS horizontal pos error too high

Are there any simple work arounds for this situation?

I undertook a few small surveys after this message popped up during the set up and then went away - the result using WebODM (without GCP's) was that 50% of the images were rejected during the processing. I am assuming that this is because the GPS accuracy was filtered and found not to be good enough???

Are there any fixes or procedures to prevent this? Perhaps hovering higher in the sky (120m) to gain better satellite HDOP fixes? Perhaps compass calibration?

Not knowing whether the photos are going to meet the quality filter until after the mission is a problem for me as it often requires a re-fly.

Any tips or advice would be greatly appreciated.

cheers
Ben

All you can do is have the drone on long enough to collect its own satellites before you start planning. The issue is with acquiring a good enough base station connection or internet connection for NTRIP and the drone having at least seven satellites.

 

[Ben H]

I just purchased an H520 E and was about to conduct a maiden flight and got this error message also. I know how the H520 is so temperamental and have had 2 mishaps with it. I abandoned the flight and packed it back up. Can anyone tell me what this means and how to ensure i have enough GPS to fly in angle mode. I am flying near a cell tower would that cause this issue with controls? The weather was cold and cloudy today.

 

[chascoadmin]

Your only choices are to wait, move to a different location or manually take off and let it sit in the air for a minute or two to see if it collects more satellites. One thing that I wish they would provide is a way to see the connections to the satellites themselves. You could have 10 satellites in view but only five of them that have a good enough connection.

 

[MNowrangi]

[14:25:59.440] Warning Preflight: GPS horizontal pos error too high

Are there any simple work arounds for this situation?

I undertook a few small surveys after this message popped up during the set up and then went away - the result using WebODM (without GCP's) was that 50% of the images were rejected during the processing. I am assuming that this is because the GPS accuracy was filtered and found not to be good enough???

Are there any fixes or procedures to prevent this? Perhaps hovering higher in the sky (120m) to gain better satellite HDOP fixes? Perhaps compass calibration?

Not knowing whether the photos are going to meet the quality filter until after the mission is a problem for me as it often requires a re-fly.

Any tips or advice would be greatly appreciated.

cheers
Ben

Preflight: GPS Vertical Pos Drift too high
The vehicle has failed a pre-arm check. In order to arm the vehicle, resolve the failure.

Is there a remedy for this failure on the H520E? Thank you.

 

[deezx]

Preflight: GPS Vertical Pos Drift too high
The vehicle has failed a pre-arm check. In order to arm the vehicle, resolve the failure.

Is there a remedy for this failure on the H520E? Thank you.

It might be a similar problem as with the H520, see:
h520-not-arming-gps-speed-accuracy-too-low.23174