Post

2 followers Follow
0
Avatar

Negative Elevations in processed Map

I have submitted 200 images for processing through DJI workflow and the resulting map shows all negative elevations.  I have checked the EXIF and XMP data in a large sample of my submitted images and the AbsoluteAltitude, RelativeAltitude and GPSAltitude values all look correct.  This also applies to the Ground reference image as well, its values are as what would be expected for the location

AAlt=+40.76

RAlt=+0.00

GPSAlt=40m

 

There is a post describing similar results but their cause appears to different than ours.  Any other thoughts on what would be causing the negative elevation results

 

John Liddard

Official comment

Avatar

It looks like your Ground Reference image was not detected which is why the elevation processing was off. Our system will only find ground reference images that have Absolute Altitude values within the range of -3 and 3 meters. This might have something to do with it being downscaled to .25. I bet processing it at native resolution would work. 

You flew at 105-ish meters AGL. GPS derived altitude values are notorious for being way off so that value basically got subtracted and you ended up with negative elevations. 

Again, this is likely an issue with takeoff tags not surviving the downscaling process. We will look into that.  

Zane
Comment actions Permalink

Please sign in to leave a comment.

4 comments

0
Avatar

One additional note is that when the images are processed using an alternate mapping service the elevations are correct and very accurate.  

John Liddard 0 votes
Comment actions Permalink
0
Avatar

The Ground Reference image not being detected is the key.  This account was used to try and trouble shoot the problem thinking it may have been an account issue.  When we used our main account (flitelab) at full resolution we encountered the same results.  We also tried a submission without the ground reference image and received the same results.  Is there a way to ensure the ground reference image is recognized as all its meta data looks correct?

John Liddard 0 votes
Comment actions Permalink
0
Avatar

You ran a non-downscaled dataset that had negative elevations. We did find the ground reference image on that one. It showed the takeoff image being taken at 33m ASL. The altitudes are just off. It is likely something to do with how the data was collected. The overlap is a little thing and the white balance is kind of all over the place which isn't going to help things. 

As noted in the Data Collection guidelines we recommend using 80% overlap when crops are involved. 

For the latest downscaled ones it does seem there is an issue getting the tags for the image after the downscaling is applied. We will try to address that shortly. The ground reference being there will make a roughly 10 meter difference in this case since the GPS said it was at 40ish vs the 33 m according to Google Earth.

Zane 0 votes
Comment actions Permalink