Photo set with multiple home point references

I am new to photogrammetry and thought I would give WebODM a try in an attempt to create an elevation model of a 20 acre property that runs up a hill, so that we can see where it makes sense to cut a road up through the property to a place to build a cabin. I flew 3 missions from 3 different points on the property, taking roughly 300 images. WebODM appears to have normalized the reference points resulting in a flat model instead of a slopped model. I used the default settings for processing. I have included the model side view where you can see the images and the orbits on the same plane only tilted, an image from google earth that shows the land is actually slopped, and the terrain model. Can anyone advise if there is a way to fix the model to align with the correct elevation climb? Thank you in advance for your help.

WebODM Model Side View:!AjBrUG9RUb7Fg5sXa0EVGuONpvdwyw?e=FG0mAK
Google Earth Side View:!AjBrUG9RUb7Fg5sV5BnM6iIsWPiYyw?e=LbRvnB

Additional image:
WebODM Surface Model:!AjBrUG9RUb7Fg5sW4c9lbXL8pP0vUw?e=KtsTgD

There’s two conditions under which this can happen: your images didn’t have GPS or the assumed (or real) GPS error exceeds the change in elevation.

The first is hard, the second might be easy.

Can you share one (or all) of the raw images?


They definitely have GPS data. I think it would be odd that the elevation discrepancy is due to error, considering that it is so perfectly flat, but the elevation change is roughly 200 ft so three equally spaced points could be within the margin of error. If that is the case, any idea how to correct it?

I was unable to post the repository from OneDrive for some reason, so I uploaded 1 image from each mission here: Plot Images - Google Drive

It looks like you got caught in our automated spam filter for posting too many links as a new user.

I have escalated your user type, so you should be able to post the link. If there’s GPS in the metadata, it will be beneficial to see the entire set.

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Thank you, here is the link the full set:!AjBrUG9RUb7Fg5hauMl0ocM2JeraKQ?e=1xNBww.

Looking at the properties of a few of the photos, it looks like the altitude is set relative to the home point, instead of relative to sea level. Short of editing the meta data 1 by 1 is there a way to correct that?

I will check to see if that is a setting on the drone for next time I fly.

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That’ll do it.

What sUAS are you using, and do you have the flight logs?

I’m using a Mavic Air 2. I just now learned that it keeps flight logs (the more you know!), I have since formatted the SD card I was using, but I can check to see if the controller stores them somewhere else. Worst case I can guess at the reference altitudes, it would be closer than not having them at all.

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Exiftool (and other tools) can bulk update elevations with an offset.

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I found the flight logs intact on the controller, yay! Downside is that one needs another program to translate them into a readable format to get the altitude information (using DatCon). I will try using Exiftool to bulk offset the images. Thank you both for your help!


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