Altitude Data is Wrong

[John]

I've recently learned that my Inspire 1 (converted to a Pro) is recording the wrong altitude in each image's metadata. The controller, aircraft, camera, and DJI Go App all have the most current F/W version (v1.10.1.40 & v3.1.1.). Altitude @ ground level should be 145.992m (479' according to USGS) but was recorded at 71.35m (234.09') on 12/12/16. On 12/16 it recorded 169.01m (554.51'), then 169.85 (557.2)7 after a battery change, then 166.22m (545.34') after an IMU calibration. DJI's response to the case I had them open (CAS-365605-F6Y3B0) was: "We would love to try our best to solve your problem, however, we are sorry to inform you that the warranty period of you drone has already expired. Its activation date was 2015/08/25 (GMT+8, 1 year warranty since then). Therefore, we could not provide warranty service no matter what caused the incident."

I've seen posts in December 2015 reporting the same problem. A tag-fix utility is available at extra cost and time per dataset.

1) Does anyone have information on what may be causing the erroneous data? Aircraft barometer? Controller? IMU calibration procedure? Other?

2) Has anyone fixed this issue and how?

Many thanks.

 

[southerndoug]

Hi John, you may know this already, but my take on it is the image tag is recording the unit's GPS altitude, which will always be out by a large amount. The barometer will record altitude relative to take off location, and will be somewhere in the flight log, but not associated with your GPS lat/long/altitude. Mapping software like that used by Maps Made Easy takes your GPS lat/long and compares it to known elevations (e.g. from http://open.mapquestapi.com/elevation/), and ditches the GPS altitude.
So there's probably nothing wrong with your barometer, controller or IMU. Just lousy altitude data from the GPS.

 

[John]

Southern Doug... The image referenced in my post was taken on the ground. Therefore, based on your reply, I'd expect near zero altitude, not 71.35m as was written in the metadata.

I have some new inexplicable observations....

• Paired the aircraft (N71EV) with another master controller I had from my N70EV I1 aircraft. Altitude read 2.26m (7.4') while sitting on a 3.3' tall cabinet - closer to ground level.
• I tried to pair it with the slave for the N70EV but the app wouldn't see the controller (it had never been used since the January 2015 purchase date so I expect it's F/W is too old for the current app to recognize).
• Re-paired the aircraft (N71EV) back with its original N71EV controller and 1.46m (4.78') was recorded on the 3.3' tall cabinet
• Took the aircraft outside, set it on the ground, and took two images. Altitude recorded in 1st pic was .23m (0.74') and .22m (.73') in the second pic.

I wonder if pairing the aircraft with the other controller reset something.

But yes, reading Pix4D & Maps Made Easy posts, GCPs are a must. The Agisoft Photoscan Pro bases contour lines from the recorded altitude in the metadata. To compensate for the erroneous altitude data in my original post, I had to use Maps Made Easy tag-fix utility to get correct contour line values.

 

[southerndoug]

Southern Doug... The image referenced in my post was taken on the ground. Therefore, based on your reply, I'd expect near zero altitude, not 71.35m as was written in the metadata.

I have some new inexplicable observations....

• Paired the aircraft (N71EV) with another master controller I had from my N70EV I1 aircraft. Altitude read 2.26m (7.4') while sitting on a 3.3' tall cabinet - closer to ground level.
• I tried to pair it with the slave for the N70EV but the app wouldn't see the controller (it had never been used since the January 2015 purchase date so I expect it's F/W is too old for the current app to recognize).
• Re-paired the aircraft (N71EV) back with its original N71EV controller and 1.46m (4.78') was recorded on the 3.3' tall cabinet
• Took the aircraft outside, set it on the ground, and took two images. Altitude recorded in 1st pic was .23m (0.74') and .22m (.73') in the second pic.

I wonder if pairing the aircraft with the other controller reset something.

But yes, reading Pix4D & Maps Made Easy posts, GCPs are a must. The Agisoft Photoscan Pro bases contour lines from the recorded altitude in the metadata. To compensate for the erroneous altitude data in my original post, I had to use Maps Made Easy tag-fix utility to get correct contour line values.

Yeah John, your barometric altitude would reference as zero on the ground, but the GPS height could be almost anything (whatever the WGS84 geoid height may be in your area) and that is what is getting written to your metadata. At my flying field, I was getting geotag metadata reports of -41.6m (on ground) and 16.3m (at flight height of 60m). I'm at sea level (well, just above).

 

[John]

Yeah John, your barometric altitude would reference as zero on the ground, but the GPS height could be almost anything (whatever the WGS84 geoid height may be in your area) and that is what is getting written to your metadata. At my flying field, I was getting geotag metadata reports of -41.6m (on ground) and 16.3m (at flight height of 60m). I'm at sea level (well, just above).

Hmmm, Disheartening, but the nature of the beast I suppose. Thanks.

 

[StealthChaser]

I fly AG all the time with DroneDeploy and DataMapper. I use Inspire 1.

Altitude is 100% recorded incorrect when flying RGB X3 camera. However when I switch camera to use my IR-Pro X3 camera the elevation is correct.

I fly the exact same flight plans every week. And every week I have to have DataMapper change my meta data to show the correct altitude.

All flights are flown at 200' AGL, but default X3 records 60' feet while the IR-Pro X3 records 200'.

DJI sucks at resolving. My workaround is tweaking the metadata manually to match altitude I actually flew. In AG world several algorithms require a minimal cm of accuracy prior for the algorithm to work, so with the altitude inaccuracy I have to fudge the metadata prior to processing.