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Proceedings of the Symposium on Progress in Data Processing and Analysis

Camera Calibration at NOS
The NOS stellar camera calibration facility at Cloudcroft, New
Mexico, was used for the last time in 1987 to calibrate super-wide
and wide-angle cones for WILD RC-10 and RC-8 aerial mapping cameras.
NOS presently uses the U.S. Geological Survey (USGS) multicollimator
camera calibration facility at Reston, Virginia.
The NOS stellar camera calibration system achieves +/-1 micro-meter
accuracy. It employs a series of accurately timed exposures of a
stellar field to determine the internal geometry of frame cameras and
lens cones. The procedure results in the most comprehensive
determination of camera constants available to the photogrammetric
user. The following camera parameters, which are also reported in
table 1, are determined:
o calibrated principal distance
o radial symmetric lens distortion model coefficients
o decentering lens distortion model coefficients
o orientation angle of the axis of maximum tangential
o coordinates of principal point and calibrated fiducial
o calibrated reseau coordinates (for cameras equipped with
Moreover, the calibration is in a form directly usable in the digital
environment of the IDPF.
The USGS multicollimator camera calibration method (Tayman, 1984)
claims +/-5 micrometers accuracy of determination of geometric
parameters, such as focal length, symmetric radial lens distortion,
and so forth. However, the manner in which the lens distortion
characteristics are determined and reported precludes its direct use
by the digital photogrammetric systems. It requires some sort of
interpolation scheme, based on the assumption that the lens system is
free of decentering distortion anomalies. In cases where decentering
lens distortions are present to a significant degree, the application
of distortion corrections will give less than +/-5 micrometer
accuracy results. This camera calibration system is limited to the
determination of the following camera constants:
o calibrated principal distance
o radial lens distortion (for the four radii, along the main
' o coordinates of principal point and fiducials
o distances between fiducial marks
This method does not meet the + /-1 to +/-3 micrometers NOS high-
accuracy requirement. While the NOS stellar camera calibration
provides the best possible calibration quality (+/-1 micrometer), it
does so at a significantly higher cost. Operational and maintenance
costs of the stellar camera calibration facility precludes its
frequent use for calibrating all of the standard NOS cameras. For
these reasons, a modified camera calibration system has been
developed. The capabilities of the USGS facility for multicollimator
imaging and the NOS high-accuracy measurement and data reduction for
stellar calibration has been combined into a new NOS camera
calibration system.
The NOS camera calibration system can technically be called a
multiexposure, multicollimator camera calibration system. Multiple