sensor_database.md

Calibration Database

Overview

Structure-from-motion needs accurate estimates of the imaging sensor geometry: lens type, focal length, distortion, and principal point. See geometry.md for the full list of camera calibration parameters.

During reconstruction, OpenSfM adjusts calibration values to best explain the observed geometry. However, starting with a good initial guess produces better and more reliable results. By default, OpenSfM reads focal length from image EXIFs. When EXIF values are missing, incorrect, or insufficient, the calibration databases fill the gap.

Calibration databases are stored under opensfm/data/:

• sensor_data_detailed.json
• sensor_data.json
• camera_calibration.yaml

sensor_data_detailed.json

Contains physical sensor width and height (in millimetres) for a given model make sensor. When only focal length is available from EXIF, the full sensor geometry can be recovered using this physical size.

sensor_data.json

Contains a multiplicative factor for a given model make sensor. Applied to the EXIF focal length, this factor gives the 35mm equivalent focal length. Since the 35mm equivalent dimensions (24×32 mm) are known, the full sensor geometry can be recovered.

camera_calibration.yaml

Contains full camera calibration definitions in OpenSfM format, keyed by make. Within each make, calibrations are further refined:

• ALL: the calibration is valid for all make model combinations, regardless of model
• MODEL: calibrations are per actual model
• FOCAL: calibrations are per focal length read from EXIF