Need help debugging reconstruction failures

[abhishek-carbon3d]

I am trying to reconstruct a scene using ~20 photos from a recent iphone camera (not in the openMVG database), but the reconstruction fails with a cryptic message "Invalid input image graph for global SfM". I have high level familiarity with sfm pipelines and would like to look into it. Are there any log files that may have more information?

FWIW the same data sample works okay with other pipelines like MVE and colmap (I am trying to evaluate a few wrt robustness, accuracy etc for my application).

Any pointers will be appreciated. Also please let me know if this is not the right forum to ask for such help. I also sent a message to openmvg-team@googlegroups.com but havent heard anything.

Thanks

[pmoulon]

I think the first stage does not detect a valid focal length and so no matches are generated.

1- check that SfMInit_ImageListing is listing at list 1 intrinsic.
You can either add your IPhone model to the database or use the -f X option to specify an approximate focal length. X will be equal to 1.2*max(w,h).

2- check that you obtain a matches.f.txt or matches.e.txt. The name will depends of the pipeline your choose (f -> Sequential/Incremental SfM, e->global SfM).

3- If you check 1 and 2 everything will run smoothly.

You can also share your dataset, or help to update the database with your IPhone camera model info thanks to a PR on github ;-)

[abhishek-carbon3d]

Thanks for the quick response. Missing focal length was the problem. I saw warning messages but assumed it will fallback to something reasonable. I am using an iphone X which has a focal length of 4mm (28mm for 35mm equivalent) and the image size is 3024x4032. Shouldn't X be 0.8*max(w,h)? Happy to send you a PR for updating the database but it seems to want sensor size?

…

On Wed, Jan 10, 2018 at 3:15 PM, Pierre Moulon ***@***.***> wrote: I think the first stage does not detect a valid focal length and so no matches are generated. 1- check that SfMInit_ImageListing is listing at list 1 intrinsic. You can either add your IPhone model to the database or use the -f X option to specify an approximate focal length. X will be equal to 1.2*max(w,h). 2- check that you obtain a matches.f.txt or matches.e.txt. The name will depends of the pipeline your choose (f -> Sequential/Incremental SfM, e->global SfM). 3- If you check 1 and 2 everything will run smoothly. You can also share your dataset, or help to update the database with your IPhone camera model info thanks to a PR on github ;-) — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#1203 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AJNkXg24-429lP9JbW_ng91BL_VzefAiks5tJUSjgaJpZM4RaFbf> .

-- -Abhishek

[pmoulon]

Shouldn't X be 0.8*max(w,h)?

• 1.2 is a generic rules. Depending of your camera fov you can use a value in [0.7;1.2].

The best way to handle this would be to add the IphoneX in the camera sensor database.
Do you can share here one of your image so this way I will be sure to have the right Camera Model and Maker name?
Additionally if you find the camera sensor size it would be great.

[abhishek-carbon3d]

Here are the exif data for 1x and 2x zoom levels

https://drive.google.com/file/d/1esby1_iqeSB3kA_1ifoiZ5x210tq0czf/view?usp=sharing

https://drive.google.com/file/d/1TUh90meLFdVz7X5Q3EZZrUfgeYp8lid0/view?usp=sharing

Unfortunately I could not find reliable info on sensor size in this data or the wen in general.

[abhishek-carbon3d]

Would it make sense to default (with a warning log) the focal length to just max(w,h) in case the intrinsics are missing from the database?

[pmoulon]

I think the sensor size is 1/3" so 4.80 mm must be the sensor width.

According your metadata, it gives Fpix = std::max ( width, height ) * focalmm / ccdw = 3291 = 4032 * 4 / 4.9

Internet seems confused and cannot decide if the sensor size is 1/2.8" or 1/3"
https://forums.macrumors.com/threads/8-8-x-has-the-same-sensor-size-1-3-as-6-6-where-is-the-promoted-improvement.2071530/page-4
https://www.gsmarena.com/apple_iphone_x-8858.php