Underwater orthomosaic with no GPS data

[Shaun Lee]

I am trying to create underwater orthomosaics with no GPS data but only getting 50-100 photos to auto align. Have I bought the wrong software for the job or am I not using it right? I have posted my process with screenshots and source footage here https://blog.shaunlee.co.nz/mapping-life-on-the-seafloor/ any advice appreciated! Thx 

[Alexey Pasumansky]

Hello Shaun,

Since you are using Sequential pre-selection, you wouldn't get matching points for the images from the different lines of "space invader" or "pick up sticks" scenarios or from different radius of "spiral" scenario.

If you are using "space invader" scenario and have hundreds or thousands of images, it may be reasonable to align the data in two iterations: with sequential preselection and then with estimated preselection, providing that most of the cameras are properly aligned.

As for the mesh reconstruction - using Sparse Cloud source would give you very rough model, so you may consider building the model from the depth maps with medium/high quality in Arbitrary mode. As for the texture reconstruction, I can suggest to generate it in Generic mode and then in the model view switch the view from Perspective to Orthographic, then orient the viewpoint in the desired way and use Capture View option get a kind of planar orthomosaic projection for your model.

If you continue getting many not aligned cameras in the project, please share the original image data to support@agisoft.com.

[Shaun Lee]

Thanks so much Alexey

I have tested those settings and it helps get all the images aligned but the alignment is very warped https://blog.shaunlee.co.nz/mapping-life-on-the-seafloor/

All the frames are online here (1GB) https://www.dropbox.com/sh/uw6yd1xtm78cdgc/AADooyY5sppcodu8HNCgVUaPa?dl=0

I'm happy to try any other settings/ methods you suggest.

Cheers

[Alexey Pasumansky]

Hello Shaun,

As far as I understand, the alignment stability can be improved with the input focal length and sensor pixel size (both in mm) to the Camera Calibration dialog and the consecutive fixing on the focal length.

[Shaun Lee]

Thanks so much, that worked and I have posted the settings here. https://blog.shaunlee.co.nz/mapping-life-on-the-seafloor/ I will refine the process and write it up as a 'how to kit'. Thanks again!

[SimonBrown]

Metashape Ortho mosaics are 100% the way to go with high resolution mapping of the sea floor:

With GPS:
https://dronelab.io/map/public/viewer/4d3ca968df624f7abf10f10f71bd6c1a

Without GPS:
https://dronelab.io/map/public/viewer/5be1f1e86b924bae9fef7ce209fd35e0

Both are scaled. Worth adding DEMs into the mix too:

http://deep3d.co.uk/indexes/tips-tricks-and-news/dem/

Like Alexey says, working with GoPro video will require camera calibration before processing, otherwise curved models will be created, plus GoPro have rolling shutters (less than idea, but not as good as mechanical ones) and this can introduce distortion too.