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

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[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
 
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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.
 
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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

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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.

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
 
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[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.
 

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