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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 
distortion 
o coordinates of principal point and calibrated fiducial 
o calibrated reseau coordinates (for cameras equipped with 
reseau). 
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 
diagonals) 
' 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