In DJI Flighthub 2 I created a mission that I still needs to fly. I wonder how precise the route will be flown. Is there any one who can advise?
Waypoints mission exactness
- Thread starter DroneSteef
- Start date
brett8883
Well-Known Member
I wouldn’t count on it for precision. Even if it could fly it with precision, I’d still be sure to give plenty of room for error.
Two things:
1. All your height measurements are relative to the launch point, so if you launch from anywhere other than the exact same launch point selected for the mission, elevations will be off, and intended barometric elevation changes have their own margin of error from the launch elevation. When you land, you'll see that the height is almost never back to exactly 0.
2. The accuracy of the route depends upon the accuracy of the GPS, which has its own margin of error, which depends upon the number of satellites in view, and its own inaccuracy, unless using correcting survey equipment. Golfers use GPS range finders, but they always hide measurements on the greens, stating "at the green" to hide how inaccurate they are, where people can easily see the detected position and where they actually are on the green. It can easily be off by 3-10 yards which is a 20 yard diameter circle of uncertainty! So, figure up to 10 yards in either direction.
In conclusion, the precision will vary. Others have posted overlapping video flights of the same mission, and they are close, but definitely not exactly the same! YMWV.
Only as precise as consumer GPS and the drone's barometric height sensor.
Don't use waypoints for flights that are close to obstacles.
I do understand but also want to understand how much tolerance I need to include....
Thanks for the response...it indicates that there is some tolerance but when I count in a certain percentage of
"safeness" this should be enough...
Ralph thompson
Well-Known Member
You don’t explain what yr doing that requires precision. For any surveying activity you need an RTK capable drone like the M3 Enterprise. With the Inspire 1 for non precise surveying work I used Autopilot SW (now defunct)for years and always allowed 50 feet as a rough safety margin. Before the mission, I’d fly to various points on the plan to confirm obstacle positions like tree tops, wires etc then make sure there was an additional 50 Ft for safety.
mobilehomer
Well-Known Member
It is in the manual. Look at the Specs section, it gives the GPS tolerances.
A couple of other things to watch out for and test beforehand. I've never used DJI Flighthub, so I don't know if these are an issue or not. Just something to think about.
If your first waypoint is some distance away from your takeoff location, does your drone fly a straight line from takeoff but only gradually increasing height to that waypoint? Are there obstacles to clear on the way? Or will it first take off straight up and climb to waypoint height, before then flying at altitude toward the first waypoint?
You can ensure it'll first climb/descend straight up/down by setting the first/last waypoint at a safe height directly above the planned takeoff location.
The second is, does the flight path go directly in a straight line between waypoints, or does it "smooth" the corners? If it carves a smooth arc short of the actual waypoint, you'll need to take that into account if you're planning to fly around any obstacles.
If your first waypoint is some distance away from your takeoff location, does your drone fly a straight line from takeoff but only gradually increasing height to that waypoint? Are there obstacles to clear on the way? Or will it first take off straight up and climb to waypoint height, before then flying at altitude toward the first waypoint?
You can ensure it'll first climb/descend straight up/down by setting the first/last waypoint at a safe height directly above the planned takeoff location.
The second is, does the flight path go directly in a straight line between waypoints, or does it "smooth" the corners? If it carves a smooth arc short of the actual waypoint, you'll need to take that into account if you're planning to fly around any obstacles.
I have created in Flighthub 2 a mission for my Mavic 3 and would like to understand the tolerance for the flown path created in this mission.
After flying 100's of missions, I've found the precision to be very accurate, except around a week ago, when the route flown was off by maybe 30 to 50 feet. I did a RTH when I approached a McDonald's sign. Also, almost hit some thin guy wires and lost my drone. So I'm investigating this more, but making sure I'm high enough to avoid a crash.
brett8883
Well-Known Member
I had a RTH yesterday that didn't seem right. It wasn't that close to anything. This is a brand new Mavic 3 Pro, that I paid for as a replacement for the drone that crashed. So I'm wondering if something's wrong with it's GPS. Maybe it's obstacle avoidance too. Of course, to check it, I would have to pay to ship it back to China. But I already have good evidence that it seems to be defective.
I have a theory about drones and GPS. This is only a theory.
If you take one GPS reading, the error can be what's posted on the internet. But say you're flying 15 minutes, over 5 miles, and the drone is taking at least one GPS reading a second, probably more. Would the cumulative accuracy of GPS get better? I think it would, and does, from my experience. I fly the same mission dozens of times, and the drone seems to go over the same objects in the same location over and over. It's very repeatable, until recently with this new drone.
What was unusual about your RTH ?
Unlikely.
GPS either works or it doesn't .. not somewhere in between.
You could always check to confirm whether there is actually a genuine problem or you were mistaken.
Evidence .. details ??
Consumer GPS has been around for almost 30 years and how it works is well known.
Your drone's flight controller starts checking accuracy as soon as it starts getting location data.
It won't change the colour of the sat icon on your screen to white until it is satisfied with the accuracy of the location fixes.
It continues to monitor the location data during flight and your recorded flight data includes a GPS reliability score for every 1/10th of a second during each flight
Your drone shouldn't be flying around with inaccurate GPS if you are flying out in the open where the drone has a clear, unobstructed skyview.
But if the GPS was less than accurate, that would clearly show in your recorded flight data.
So here are four videos so you can see for yourselves. The first one is the RTH I don't understand. It doesn't seem close enough to anything to justify a RTH.
This is the exact same waypoint mission. As you can see, the path is slightly to the right of the one that did a RTH.
This one is where the drone went way to the left of it's path and ran into a McDonald's sign so it did a RTH.
This one is the exact same waypoint mission as the last, except I raised the elevation in case it went toward the McDonald's sign. But you can see it was true to it's path, and went way to the right of the McDonald's sign.
This is the exact same waypoint mission. As you can see, the path is slightly to the right of the one that did a RTH.
This one is where the drone went way to the left of it's path and ran into a McDonald's sign so it did a RTH.
This one is the exact same waypoint mission as the last, except I raised the elevation in case it went toward the McDonald's sign. But you can see it was true to it's path, and went way to the right of the McDonald's sign.
That's a crazy busy environment to be creating Waypoint flights in!
Power lines and antennas popping up everywhere, along with birds flying through. Even a manual flight with full VLOS through there would be extremely challenging. Have you tried one?
Power lines and antennas popping up everywhere, along with birds flying through. Even a manual flight with full VLOS through there would be extremely challenging. Have you tried one?
The video doesn't show what didn't seem right about your RTH.
More explanation required.
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