EGM96 and other geoid models to support accurate above mean sea level heights in EXIF data

Jan S

August 13, 2024 17:03
2 comments

Hello, I use a Mavic 3 Enterprise for land surveys with the RTK module. When using the DJI Pilot 2 app, it gives the ASL option to use the EGM96 geoid model to write the actual above mean sea level heights in the EXIF of the images. When using dronelink (growth), I only have the ALT and AGL option available. This causes the drone to write ellipsoide heights in the exif files, so the heights are in my case around 48 meters higher than expected. I know there are solutions to recalculate the geoid heights from ellipsoide heights, but to use WebODM I have to manipulate the EXIF data of every image. There is no option in WebODM to use different height models. How do other people deal with that issue? They probably use high-end software like Agisoft Metashape where you can select the vertical model or got a workaround. Now I have an accurate model but the height is totally off. I can't use the model to supply my customers. Normally I just create some high resolution DTM/DSMs in WebODM, but with the ellipsoide heights, the data is worthless to me although the horizontal accuracy is ~5cm accurate. Recalculating the images EXIFs seems quiet the hustle. Do you plan to integrate vertical model selection in the future? Do you have a workflow or workaround that doesn't involve expensive software? Dronelink offers a great improvement to the DJI Pilot 2 app functionality but I'm disappointed that no geoid models are supported to write ASL heights. Maybe I'm just missing something. There are not many posts about this topic so maybe I'm missing something? Would greatly appreciate some help.

Comments

2 comments

Barry Houldsworth Dronelink Expert
- August 13, 2024 17:17
On the assumption that you had the RTK module installed on the drone when you captured the images (doesn't actually have to be running with RTK enabled) then you can use Emlid studio to make corrections to the position data and then export a set of photos with the corrected EXIF data.

I covered that in this video: https://youtu.be/cESXvYiQ5ps

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Jan S
- August 13, 2024 17:32
Hi Barry, thank you, that should be working. But I need to find a the RTK provider in Europe, the site you mentioned in your very informative video (I was following your channel before ;)) doesn't cover Europe, I think. Gonna check that out tomorrow. Thanks for the advice, I'll let you know!

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