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Retrieving Focal Length from Metadata
The (Scripts/) "Metadata/Retrieve focal length and plane" script looks at the available metadata and drives it into the seed field-of-view track. This script is the primary current use of metadata. The script handles both fixed and zooming shots. Different controls will appear in the script depending on what metadata is available.
It is crucial to have an accurate sensor (back plate) width number as well, as otherwise the focal length means nothing. Sometimes the sensor (back plate) width information is available from the metadata; if not you must acquire it from the camera specifications or from other calibration shots. In at least some cases, more metadata may be available from still images acquired as "raw" and then saved as other image types.
In the event that no better information is available, the script may use the exif_focal_length_in_35mm tag, which is the equivalent focal length, as if the camera was a 35-mm still camera. This tag is dependent on the camera manufacturer doing the math right. Unfortunately a technical issue in the EXIF data format requires that the number be a whole (integer) number, limiting its accuracy.
The script writes to the "seed" track, ie the initial suggested value for the lens field of view. Check the "Set lens mode to Known" checkbox (or set the mode yourself) to have the lens field of view used exactly for the solve. Otherwise it may be used as a starting point, or just for comparison.
If the scene has already been solved, you'll be asked if you want to clear the solved camera FOV track. If it is cleared, then the newly-created metadata-based FOV is visible directly and immediately. If not, it won't be visible unless the scene is re- solved, the solution is cleared, "View/Show seed path" is selected, or you look at it directly in the graph editor.
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