Field calibration of zoom cameras for two camera- photogrammetric applications

Abstract

To obtain reliable 3D measurements from photogrammetric technique imaging, cameras must be calibrated to determine the value of the principal distance and various lens parameters. As zoom and auto-focus are known to change, the principal distance at the instant of imaging the use of laboratory-calibrated value may produce significant measurement errors. The value of other lens parameters also may change as a result of field imaging. Research was carried out to determine a reliable technique to obtain the value of the principal distance and other lens parameters in the field. This research was limited to a stereo-camera configuration where two digital cameras were used to map objects. The calibration involved simultaneous computations of the principal distance and other lens parameters of both cameras using a pair of stereo-images and a temporary control panel. The objective of the paper is therefore to discuss the testing of the developed technique and demonstrate its capacity for a high-accuracy field 3D measurement. Results of this research show that accuracy improvement is in the order of two times better than the conventional technique which uses self-calibration PDs and APs.