3D Render is curved

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.

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?

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

In that case, try turning it on :smile:

giphy

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

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

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

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

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

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

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.

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.

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

2 Likes

IIRC this is a rolling shutter issue, typical of drones without mechanical shutters on their photographic equipment and moving too fast when acquiring data.

A few things can be done to correct for this:

  • use a drone with a camera that has a mechanical shutter (admittedly very few will follow this route), or
  • slow down (in the region of 5m/s max, the slower the better) and use a high shutter speed (1/1000s), or
  • stop the drone at each photo location, take picture, move onto next position, repeat; this method will take much longer to complete missions (you’ll probably have to resume missions as battery flight time will become an issue).

It’s true, we do not yet have rolling shutter corrections in OpenDroneMap, and slowing down or stopping the drone is the best route, short of flying with something that has a global shutter.

I’ve seen the bowling effect with surveys from P4s which have a global shutter. I think it’s regular lens distortion more than shutter.

2 Likes

I paste here a message I type on other site of the forum, so maybe some can delete my original post:

I have Phantom 4 pro and I have similar problem, if it not the same.
Any clue?
Did

Hi All, i’m pretty new and not a english speaker so I will do my best.
I use dronedeploy ios app to make a flight to process around 40 hectareas, I use 3 batteries on my phanton 4 pro dron, flighing at 80 meters I get 800 images to process.
I try few times to process them and is imposible with my computer, so I make 2 task, first one with the 0 to 400 images and other task with the 400 to 800 images.

I tell you this, because maybe have something to do with my problem, I don’t think so but, I explain anyways.

WEBODM SM:
Im pretty sure that on the field is not like a see on the image and the export file on qgis.
How can I tune fine with this?

WEBODM%20CURVAS
WEBODM%20SM

Repost from Help with an effect like "eyefish" on DEM. I’m closing this. @gabrielcz please don’t open multiple topics. :pray: