How to specify camera parameters in the case of single_camera_per_folder=1?

[ibd]

I am trying to create a script that can take stereo camera images and do a reconstruction based on that.

When I specify camera parameters manually while using single_camera_per_folder=1, all the cameras (i.e., every camera from every subfolder) will take the camera parameters.

How am I supposed to pass in the (known, pre-calibrated) camera parameters in this case?

Ideally, I would pass in a list of list of parameters, one list of parameters for every camera (since I know the number of cameras beforehand).

Another workaround I have in mind is to do the feature extraction step with single_camera_per_folder=1, then change the camera parameters via the script, but I don't see a possibility besides directly changing the SQLite database.

[Johannes Schönberger]

Your best bet is to write a small Python script that executes an SQL statement. You can have a look at the scripts/python/database.db for an example. Let me know if you have further questions. 

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[ibd]

Hi Johannes

Thank you for the support and the excellent software in general!

I was able to insert the data into the database like the following:

params = [np.array((699.316, 665.998, 378.275, -0.171522, 0.0244116)),

           np.array((700.742, 628.812, 362.365, -0.173764, 0.0265925))]

 db = sqlite3.connect(dbPath)

 for i in range(len(params)):

   sqlCommand = "UPDATE cameras SET params=(?), prior_focal_length=1 WHERE camera_id=%d" % (i+1)

   db.execute(sqlCommand, (np.getbuffer(params[i]),))

 db.commit() # save data back to file

 db.close()

Now I'm wondering how to use the rig bundle adjuster / how to make a .json file containing the rig setup. Is there any documentation / tutorial / explanation for that? All I found was a github issue where someone figured it out by himself. :)

Cheers

-- ibd

[Johannes Schönberger]

This should hopefully answer your question: https://github.com/colmap/colmap/blob/dev/src/exe/colmap.cc#L1179

Let me know if anything is unclear.

Cheers, Johannes

[ibd]

Thank you, I finally got it working! I had some problems at first, but I found that it was related to my file naming.

One thing I'm confused as of yet: I would like to retrieve absolute scaling of the reconstruction, as given by the stereo system. Yet, there's no way to specify the extrinsics (baseline) for the camera. I have seen in the code that this is on your TODO list.

OTOH, I have also seen that there are "ComputeScale()" and related methods. Do they work with the rig extrinsics?

If it's not possible to specify the baseline (or stereo camera rotation R / translation t) explicitly through the .json or CLI, is there otherwise a way to modify the database to contain that info?

[Johannes Schönberger]

The extrinsic parameters of the rig configuration is  urgently automatically computed from the sparse reconstruction. Scaling of the model could be done as a post processing step by loading the model using e.g. the provided Python or MATLAB scripts in scripts/python/read_model.py. I am planning to soon add more camera rig functionality. 

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