3D Render is curved

#1

Hi All,

This last week I mapped some property, the total elevation change is less than 1.5 meters from the highest ground elevation to the lowest. My 3D render, however, comes out very curved, as if it’s projected onto the inside of a sphere. You can see this in the attached gif image below:

2019-04-11_23-33-49

What causes this, and how can I avoid it in the future? The 3D model made while processing the images in Metashape came out flat, not bowl-shaped, as expected. I’d include a screenshot, but Metashape is still processing data and I can’t get a good image right now.

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#2

One issue I’ve found is that for small areas (< ~500mx500m) I need to use “use-fixed-camera-params” as I get an upside-down bowl shape (the opposite to what you see). For larger areas (> 1km square), if I have that option on, it creates what you’re seeing. So I have to turn that option off.

It’s a bit tricky finding a happy medium. I like to automate stuff, so it’s on the list to work out the total area size before processing and toggle the option automatically for the best results. I already automatically pull out the GPS EXIF data to make applying GCPs easier (a few clicks) so I’m halfway there already. Just need to find the time for the rest.

Edit: I forgot to ask the (implied) question. Are you using “use-fixed-camera-params”, and if so, have you tried turning it off?

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#3

No, I was not aware of that flag, or what it does.

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#4

In that case, try turning it on :smile:

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#5

giphy

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#6

I’m running the dataset again to see how it turns out. Thanks for pointing out the flag.

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#7

Turning it on did the trick. Thanks for the info.

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#8

I’m curious: what is your sensor? Is this a DJI?

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#9

Most likely. I’ve seen this with photos from Mavic Pros and Phantom 4s.

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#10

Phantom 4 Advanced. Same camera as the Phantom 4 Pro v1 and v2.

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#11

This is probably a result of the images already being undistorted before being fed into ODM.

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#12

Agreed, though there’s an odd issue with very large datasets where turning this on actually has a negative effect. It seems to undistort it too much. Or, perhaps more likely, the anti-distortion effect is too much in every case but is more noticeable on larger datasets because it’s amplified further with each image.

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#13

The images were loaded straight from the memory card to WebODM. Unless they are getting undistorted on the drone itself, I’m not sure how it would be happening.

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#14

Yes, the DJIs compensate for this on JPGs but not RAW. It looks like they’re still doing this even with the Mavic 2: https://forum.dji.com/thread-167508-1-1.html

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