Mavic 2 Enterprise Advanced Altitude Questions.

[jaja6009]

I have just saw something interesting that I hadn't picked up on. I do not know if this is just my aircraft or every one's.
What altitude is in the metadata for the images?

For a flight where I was 84' AGL I have an altitude of 8.145 meters given. The takeoff area's true altitude is probably around 2 to 3 meters above MSL.

Pix4D assumes the Mavic 2 EA to be in WGS84 with height in meters and using EGM96 for the Geoid. If I do some math though the 8.145 meters would make sense if it was -8.145 and the height was given as height above (Or in this case below) ellipsoid and this value is the ellipsoid value with no geoid applied.

I do know that the Phantom 4 RTK outputs in WGS84 and height above ellipsoid.

Anyone got the answer?

 

[Meta4]

What altitude is in the metadata for the images?

Unless your drone is different from all other Mavics, it will have two different heights in the image metadata.
But you'll only see one with the common ways that most people view metadata.
An additional problem comes from DJI labelling one of those heights as GPS Altitude when it did not come from GPS.

Post one of your full-sized jpg images and I'll show you what the metadata shows for altitude.

 

[sar104]

The M2EA EXIF altitude data has 4 relevant entries:

GPS Altitude Ref : Above Sea Level
Absolute Altitude : +1499.06
Relative Altitude : +124.15
GPS Altitude : 1499 m Above Sea Level

However, they are misnamed - none of them use GPS altitude.

GPS Altitude Ref : Above Sea Level
Absolute Altitude : Pressure altitude based on a standard atmosphere
Relative Altitude : Pressure altitude relative to the takeoff elevation
GPS Altitude : The same data as absolute altitude

 

[jaja6009]

Thanks for the replies.

Pix4D is pulling from the Absolute Altitude. When I view the Relative Altitude values it was spot on.
I'll email their Support so hopefully they will update it. For now I'll have to add a Location and Orientation file with the updated altitudes.

This forum absolutely has the best members with the correct information.

 

[sar104]

Thanks for the replies.

Pix4D is pulling from the Absolute Altitude. When I view the Relative Altitude values it was spot on.
I'll email their Support so hopefully they will update it. For now I'll have to add a Location and Orientation file with the updated altitudes.

This forum absolutely has the best members with the correct information.

What are you hoping they will change? Relative altitude could create problems too, firstly if the exact takeoff is unknown and secondly because it can also introduce errors of several percent in a non-standard atmosphere.

 

[jaja6009]

The Relative Altitude lined up with my flight height of 177 AGL almost exactly. So this will be enough to get my non-GCP maps to have somewhat close to expected elevations. The altitude that Pix4D was using was 28 meters AGL and this made my non-GCP maps severely in the negative and would of caused confusion.


I am doing a photogrammetry comparison for low cost Public Safety sUAS. I have Pix4D and the local community college lets me use their pricey Drone Deploy, so outputs will be in both platforms to show time comparisons between cloud processing and local processing with a well spec'ed by dated gaming computer.

Mavic 2 Enterprise, Mavic 2 Enterprise Advanced, Anafi Thermal, Autel Evo 2 Dual and then a Phantom 4 Pro with PPK.

All maps at 1.5 cm Ground Sampling Distance to show how the camera and focal length will have each sUAS at a different altitude and collecting a different number of images.

Each sUAS will have:

1 Map - No GCP, No Checkpoints (Out of Box)
1 Map - Checkpoints to show inaccuracy
1 Map - GCP and Checkpoints

18 Control Points measured with Emlid Reach RS2.
9 will be check points and 9 GCPs in maps with GCPs.

Final Map will be the Phantom 4 Pro with PPK and GCP's to show the low cost "gold standard" for mapping.

Others want to know how good or bad mapping is with the more common choices in Public Safety sUAS so while this is by no means a scientific study, it should be able to give a decent assessment.

The Anafi Thermal lost one of its main pluses. Parrot for some reason in the last year or so made it so you cannot use the full 21MP image, you now have to use the 16MP image. Also Evo 2 Dual only uses a 12MP image instead of its 48MP image when using their map image collector.

All sUAS collected their images on the same day flying as quick as safely possible after each other.