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Camera Calibration parameters - precalibration and autocalibration
Hello,
I wanted to ask about the 'use precalibration step' and 'Autocalibrated' checkboxes in Camera Calibration window in Zephyr in a bit more detail, as I couldn't find anything online.
My questions:
As I understand, 'autocalibrated' just serves as a flag for the type of calibration. Does the program treat the calibration settings different during sfm when this is checked? If so, how exactly? (more iterations, etc?)
What does checking 'use precalibration step' do, exactly? Does it use the exif image data to estimate ALL the parameters (focal px, k1-k3, p1, p2, cx, cy) or just some of them? Does it use anything else that could change from dataset to dataset, aside from exif data? I get that it's used in situations where no good starting guess is available, but would like to know the importance of it or its general impact on the sparse point cloud.
More details / experimentation:
After searching through the forum I've come up with the following:
I've experimented with the 'use precalibration step' and while for some datasets unchecking it doesn't seem to have much of an effect (even when no database camera info is used), for one of my datasets (top-down drone images, roughly grid formation, large barrel distortion, camera not present in zephyr's camera database) unchecking precalibration step makes the sfm reconstruction very domed and partially missing.
Example of the calibration settings for this domed dataset:
?
Any advice or correction of my assumptions if they're wrong would be much appreciated, thank you!
I wanted to ask about the 'use precalibration step' and 'Autocalibrated' checkboxes in Camera Calibration window in Zephyr in a bit more detail, as I couldn't find anything online.
My questions:
As I understand, 'autocalibrated' just serves as a flag for the type of calibration. Does the program treat the calibration settings different during sfm when this is checked? If so, how exactly? (more iterations, etc?)
What does checking 'use precalibration step' do, exactly? Does it use the exif image data to estimate ALL the parameters (focal px, k1-k3, p1, p2, cx, cy) or just some of them? Does it use anything else that could change from dataset to dataset, aside from exif data? I get that it's used in situations where no good starting guess is available, but would like to know the importance of it or its general impact on the sparse point cloud.
More details / experimentation:
After searching through the forum I've come up with the following:
- autocalibration happens when no exif data is available for the program to use (so 'Autocalibrated' is by default unchecked for datasets with exif data present)
- Image exif data is used for the pre-calibration step, so if no exif data exists (e.g. video frames) this precalibration cannot be carried out
- If the loaded parameters are already a good estimate, it's better to run the reconstruction without any precalibration step (so precalibration step overrides the input parameters)
I've experimented with the 'use precalibration step' and while for some datasets unchecking it doesn't seem to have much of an effect (even when no database camera info is used), for one of my datasets (top-down drone images, roughly grid formation, large barrel distortion, camera not present in zephyr's camera database) unchecking precalibration step makes the sfm reconstruction very domed and partially missing.
Example of the calibration settings for this domed dataset:
?Any advice or correction of my assumptions if they're wrong would be much appreciated, thank you!
(I'd imagine if EXIF data is the main source, then starting parameter estimation is harder when the only info is image size, as with sampled video frames)
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