First minor issue - GPS EXIF altitude?

[gnirtS]

Picked this up from the DJI forum ( mavic pro 2 exif GPS Altitude not working... ) and then ran tests with all the M2P DNGs i could find and seems to be true.

Looks like the EXIF altitude data is out on the file. Absolute Alt is always 1.2 and total altitude measuring several hundred miles!

Anyone getting this on their birds?

Nothing a firmware update cant fix.

 

[ST@AerialMetrics]

Confirm same EXIF altitude error on my M2P. But also Lat/Lon off by about 0.75 miles (actually could just be the Longitude that is off)

 

[parkgt]

Might be a good thing for some. Will make it harder for the Feds to use the data against them.

 

[kilomikebravo]

I like the way you think, Park.

KB

 

[Darryl]

Not so good for us who use it to do aerial mapping

 

[sar104]

Not so good for us who use it to do aerial mapping

Do you use GPS altitude for mapping?

 

[gnirtS]

A lot of photogrammetry programs need it as a base.

 

[4wd]

In one of my stills it shows altitude like this, it doesn't look right

• GPS Altitude - 114495603 m

 

[gnirtS]

That's the bug.

 

[Darryl]

How do we report bugs to DJI, this is the reason I bought this drone

 

[sar104]

A lot of photogrammetry programs need it as a base.

I'm surprised that is accurate enough. I get the reference elevation from a DEM when I need it, and then use relative altitude to compute AGL.

 

[Darryl]

It’s not accurate enough but it’s used by photogrammetry software to initially align the imagery. Imagery can still be aligned without this data but it’s not as good. Once aligned you then enter your surveyed ground control points to make the ortho/dem accurate.

 

[sar104]

It’s not accurate enough but it’s used by photogrammetry software to initially align the imagery. Imagery can still be aligned without this data but it’s not as good. Once aligned you then enter your surveyed ground control points to make the ortho/dem accurate.

That's what I'm not understanding - why would it not be better to use an accurate altitude to align the imagery?

 

[4wd]

It worked ok on the original Mavic so I expect they will fix it eventually.
You see height above sea level so not sure how useful it is really.

 

[Darryl]

That's what I'm not understanding - why would it not be better to use an accurate altitude to align the imagery?

You'd have to mount a gnss/gps receiver on the drone to get accurate altitude, even then it's only 1-2 meter accurate , they also typically require a computer to record the data to, I know this because I have full sized aircraft mapping setup with A6D Hasselblad and two gnss/imu receivers for position data. RTK would be sweet but that requires the ability to record trigger events.

I just got my new drone yesterday and checked exif data on images, altitude info shows altitude above the ground, even though in the exif data it says its above sea level. We are 2500' AGL here, and my exif data shows altitude of 100 meters/333ft which is what I was at above the ground from my take off location.

 

[gnirtS]

The EXIT has "Absolute" and "Relative". IT seems at least its the absolute field thats broken.

 

[sar104]

You'd have to mount a gnss/gps receiver on the drone to get accurate altitude, even then it's only 1-2 meter accurate , they also typically require a computer to record the data to, I know this because I have full sized aircraft mapping setup with A6D Hasselblad and two gnss/imu receivers for position data. RTK would be sweet but that requires the ability to record trigger events.

I just got my new drone yesterday and checked exif data on images, altitude info shows altitude above the ground, even though in the exif data it says its above sea level. We are 2500' AGL here, and my exif data shows altitude of 100 meters/333ft which is what I was at above the ground from my take off location.

Okay - clarification necessary before this discussion goes completely off the rails:

Firstly, my comment about using more accurate altitude data referred to using altitude relative to takeoff in conjunction with an accurate DEM, not to using a more accurate GPS.

Secondly, the DJI EXIF data shows three altitudes – the GPS altitude relative to mean sea level (derived from a geoid model) absolute altitude (intended to the same as GPS altitude) and the barometric altitude above the takeoff point. Nowhere does it record altitude AGL. The issue raised in this thread is that the GPS altitude and absolute altitude in the EXIF files is garbage. The GPS altitude is over 110,000 km, and the absolute altitude is always 1.2 m, even though the aircraft is correctly logging the actual GPS altitude in the DAT file. The relative altitude is correct.

I don't understand your comment that you are at 2500 ft AGL. You presumably mean 2500 ft MSL. The EXIF data that you are referring to, if this is a Mavic 2, is the barometrically derived altitude above takeoff point - the "relative altitude" field in the XMP section of the EXIF.

 

[ST@AerialMetrics]

On my M2P, not only is the GPS altitude over 100km, but the Lat and Lon are typically off by up to a mile (based on having mapped 4 areas now). The Mavic 1 and Inspire were always within feet at worst. I've been able to fool Pix4D (photogrammetry software) into correctly rendering and placing models from M2P images, but obviously eager for a corrective DJI firmware update.

 

[kilomikebravo]

ST: I tried many programming languages over the years but you’re either a coder or you’re not it just took me a long time to figure that out.

That said, from what little I can gather of the work you do it truly sounds interesting. Do hope DJI fixes it for you soon.

KB

 

[sar104]

On my M2P, not only is the GPS altitude over 100km, but the Lat and Lon are typically off by up to a mile (based on having mapped 4 areas now). The Mavic 1 and Inspire were always within feet at worst. I've been able to fool Pix4D (photogrammetry software) into correctly rendering and placing models from M2P images, but obviously eager for a corrective DJI firmware update.

The lat/long on mine are spot on, and agree with the logged position data. Is the lat/long in your EXIF data the same or different to the aircraft position data in the log file?