CORRELATION OF DATA FROM VARIOUS
METHODS OF AERIAL CAMERA CALIBRATION
Robert M. Spriggs
Aerial mapping cameras must be accurately calibrated to determine
the radial and tangential distortions in the lens-camera system and to
compute the calibrated focal length of the camera if aerial maps with
a high degree of accuracy are to result* The Air Force first used the
field calibration range for calibrating aerial cameras; this calibration
range was constructed at Wright-Patterson Air Force Base. Similar
ranges were constructed later at Brookley Air Force Base (MOAMA) and
Hill Air Force Base (OOAMA) for use of the depots in maintaining Air
Force cameras.
Although the calibration range is an accurate method of calibrat
ing mapping cameras, considerable space is required for this type of
installation and its use is often inconvenient and limited by weather
conditions. An accurate laboratory method, therefore, would be more
desirable. Two laboratory devices--the collimator bank and the goniometer
--are in current use by commercial and governmental agencies for camera
calibration. The National Bureau of Standards has used a multicollimator
bank for a number of years, and the Fairchild Camera & Instrument Corpor
ation uses an instrument of similar principle. In order to produce a
collimator-type instrument of simpler design, a contract was negotiated
several years ago with the Perkin-Elmer Corporation, and an instrument
was built for the Aerial Reconnaissance Laboratory. In the collimator-
type instruments (and the field range, also) the cameras are calibrated
by reproducing special targets photographically on glass plates, measur
ing their images on a comparator, and analyzing the results mathematically
to produce a calibrated camera focal length and a lens distortion curve.
The T-4 goniometer is a commercial device developed by the Wild
Instrument Company. This instrument provides a visual method of camera
calibration by permitting the observer to view the target against a
graduated plate through the lens of the camera. This particular gonio
meter measures radial distortion but cannot measure tangential distortion;
the Wild Company has developed a later model with a filar-type eyepiece
which can be used to measure both radial and tangential distortion.
Although close correlation was known to exist between computations
made on the field range and on the collimating devices, no information
was available as to their correlation with the goniometer technique.
A series of tests was conducted to determine this correlation. This
report presents the results of these tests.
This paper updates a Technical Report written by the author and
published as WADD Technical Report 60-423, "Correlation of Data from
Various Methods Camera Calibration", 5 March 1959, Wright Air Develop
ment Division.
AF-WP-O-AUG 6 4 2M