Camera Calibration is the process of determining the internal characteristics of a camera so it can be used as a measurement device.
PhotoModeler can use photographs taken by different types of cameras. For PhotoModeler to use the image information in a photograph, it needs values for some specific parameters of the camera. Generally we need to know the focal length of the lens, the digitizing scale (which is the CCD format size of a scanner or digital camera) and the principal point (where the optical axis of the lens intersects the photograph). To get improved accuracy, we also use parameters that describe the distortion characteristics of the lens.
Camera calibration is a method for accurately determining values for these camera parameters. Once a camera is calibrated, it will provide accurate measurements.
Cameras calibrated in Version 6 or later store additional information to help gauge the quality of the calibration result. The Overall Residual RMS (in pixels) and the Maximum Residual (in pixels) provide useful feedback about the success of the calibration and are especially useful when comparing two calibrations of the same camera/lens. The Photo Coverage (%) (see Visibility Settings, Point Coverage setting in the Camera station section) indicates what portion of the lens has been calibrated. A calibration can only solve for the part of the lens on which are referenced points, so the boundary is a way to gauge visually how much of the lens is calibrated. You’ll want all of your points in your model projects within this boundary. The Camera Viewer Dialog shows these quality indicators.
Note: the Camera Calibration calibrates both the camera and the device used to convert the photographs to digital form (scanner or digitizer) as one unit. If the scanner or digitizer is changed then the calibration should be redone (applies to film and video cameras but not digital cameras).
Once a calibration is completed, if it is successful and the images have sufficient EXIF data, you will be prompted to add the camera to the Camera Library. Cameras in the camera library are automatically searched when adding photos to a project as part of the Camera Matching feature. It is a good idea to store your well calibrated camera in the library, but it is still possible to load cameras (in the new project wizard or manually) by browsing for project (.pmr) or camera (.cam) files on disk.