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Mavic 3E ASL Altitude Waypoint planning
3102 11 2023-11-29
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M1k3y
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I'm currently working on a project using the Mavic 3E, and I'm having some difficulties with setting up a waypoint mission with ASL altitudes. I've been using altitudes derived from previously taken images, and I need to recreate them reliably in my mission.

Here's what I've been doing so far:

Altitudes from Previous Images: I have ASL altitudes from images I've captured in the past. These altitudes are crucial for the accuracy of my current project.

Waypoint Mission Setup: I've been trying to set up a waypoint mission in the Mavic 3E with these ASL altitudes. However, it seems like the drone isn't flying to the correct altitudes I've inputted.

Reliability Concerns: The challenge I'm facing is ensuring the reliability of the altitude settings. I need the Mavic 3E to consistently fly to the specified ASL altitudes to maintain the accuracy of my project.

If anyone has experience with setting up waypoint missions on the Mavic 3E using ASL altitudes, I would greatly appreciate any insights or tips you could share. Are there any specific steps or considerations I might be missing? Is there a particular way to input ASL altitudes that I need to be aware of?

Additionally, if you've encountered similar issues or have successfully implemented ASL altitudes in your projects, your guidance would be invaluable.

2023-11-29
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M1k3y
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I tried using Absolute Altitude from EXIF data, but the drone consistently flies lower than expected during tests.  To correct, I calculated the difference and adjusted the altitude, but it's still too low.
2023-11-29
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Mobilehomer
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All the Mavic 3 altitudes are from takeoff point. You may be successful if you can get that exact ASL altitude and adjust from that.
2023-11-29
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Labroides
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M1k3y Posted at 11-29 14:25
I tried using Absolute Altitude from EXIF data, but the drone consistently flies lower than expected during tests.  To correct, I calculated the difference and adjusted the altitude, but it's still too low.

I tried using Absolute Altitude from EXIF data, but the drone consistently flies lower than expected during tests.
If the Mavic 3 Enterprise camera is like all other DJI cameras, you'll always have problems doing that.
The Absolute Altitude shown in EXIF info is not what you think.
It's completely useless and varies with weather conditions, sometimes +/- 200 feet or more.
2023-11-29
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LV_Forestry
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The drone does not work in ASL but in WGS84. If you took the ASL altitudes from the EXIF you must convert them via EGM96. Or read the original WGS84 altitude.

But in the flight plan it doesn't work that way. It is an altitude relative to the takeoff point.

You must always use the same starting altitude (the same starting point for each flight). The RTK must be FIXed.

Then you do (ASL or WGS altitude of the photos minus ASL or WGS altitude of the starting point) = Relative altitude of the images relating to the starting point, it is this value that you must enter in the flight plan.

By doing this I obtain datasets which overlap +/- 5cm in Z.


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2023-11-29
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M1k3y
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Mobilehomer Posted at 11-29 16:00
All the Mavic 3 altitudes are from takeoff point. You may be successful if you can get that exact ASL altitude and adjust from that.

Yep I tried that, I found the approx. ground level online and added that to the AGL extracted from the EXIF data and I was still coming out low.
2023-11-30
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M1k3y
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LV_Forestry Posted at 11-29 23:33
The drone does not work in ASL but in WGS84. If you took the ASL altitudes from the EXIF you must convert them via EGM96. Or read the original WGS84 altitude.

But in the flight plan it doesn't work that way. It is an altitude relative to the takeoff point.

But in the flight plan it doesn't work that way. It is an altitude relative to the takeoff point.\
You must always use the same starting altitude (the same starting point for each flight). The RTK must be FIXed.


Then what is the point of the ASL (EGM96) flight setting?

Then you do (ASL or WGS altitude of the photos minus ASL or WGS altitude of the starting point) = Relative altitude of the images relating to the starting point, it is this value that you must enter in the flight plan.

Ill try this but I am trying to set up the flight plans so that the images are taken in the same spot regardless of takeoff point as the flight location is under heavy construction and the same takeoff points may not always be available
2023-11-30
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M1k3y
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Also its worth mentioning that I was given these photos from a few different flights and I dont have the original take off locations available.
2023-11-30
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LV_Forestry
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M1k3y Posted at 11-30 07:06
But in the flight plan it doesn't work that way. It is an altitude relative to the takeoff point.\
You must always use the same starting altitude (the same starting point for each flight). The RTK must be FIXed.

ASL mode is theoretically what would suit what you want to do. But the resolution of the EGM96 is so low that it is not accurate at all. There is no indication of how the geoid interpolation is done.

For what you want to do the best option is to work in ALT mode, i.e. always taking the same target to surface starting from the same point. Either by measuring the starting point and modifying the target to surface accordingly. This I am sure will work. See the screenshot that I put in my first response.
2023-11-30
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Labroides
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M1k3y Posted at 11-30 06:59
Yep I tried that, I found the approx. ground level online and added that to the AGL extracted from the EXIF data and I was still coming out low.

I found the approx. ground level online and added that to the AGL extracted from the EXIF data and I was still coming out low.
You've completely ignored my previous post.
And you've assumed that the Absolute Altitude from EXIf is actually a height above sea level.

Here's an example photo.
https://drive.google.com/file/d/1DQ8w7sgcjNRzf8OZV_zgTorT8SNcL90n/view?usp=drive_link
Look at the Absolute Height and think again.
2023-11-30
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M1k3y
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So I have finally solved it. The altitude settings for the ASL flight plan are orthometric elevations in EGM96 and the Absolute Altitude in the EXIF are ellipsoidal elevations in WGS84. After correcting for that I have tested it with two different take off points with varying elevations and the images were within 0.2' which is good enough for these purposes. I will test again tomorrow when the barometric pressure is different and report back.
2023-11-30
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LV_Forestry
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By definition ASL = Orthometric. I assumed you knew about this.

I reiterate, pay attention to the resolution of the EGM. If you want to convert to NAVD afterwards, it is better to stay in WGS.
2023-11-30
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