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Photogrammetric Calibration of Television Systems 
by Dr. Kam W. Wong 
INTRODUCTION 
A television mapping system is consisted of three basic 
components: J)'a TV camera, 2) a transmission channel, and 3) 
a receiving sub-system. Within the receiving sub-system, the 
video signal may be displayed on a cathode ray tube (CRT) and 
then photographed by an optical camera. In a more advanced 
system, the video signal may be used to expose a photographic 
film by means of either an electron beam or a laser beam re- 
corder. 
For mapping applications, it is convenient to treat the 
entire TV system as an optical photographic system obeying the 
law of central perspective. It is therefore necessary to 
calibrate the equivalent focal length, the principal point, and 
the internal geometric distortions of the entire TV system. 
Because of the large electronic distortions present in a 
TV system, accurate calibration of the internal geometry must 
necessarily be consisted of two stages: 1) determination of the 
geometric distortions introduced between the target plate of 
the TV camera tube and the final photographic image, and 2) 
determination of the internal geometry of.the optical lens 
system in front of the camera tube including thé focal length, 
principal po#nt and lens distortions. ; 
The work in stage 1 is best accomplished by etching a 
reseau pattern onto the photoconductive target of the TV camera 
tube. The coordinates of the reseau points must be accurately 
measured. As the electronic image on the target is scanned and 
the resultant video signal is transmitted through the communica- 
tion channel to be reconstructed into a visual image at the re- 
ceiving station, the reseau image undergoes the same electronic 
distortions as the photographic image and will appear in every 
frame. Thus by comparing the image coordinates of the reseau 
points with their corresponding calibrated target coordinates, 
geometric distortions over the entire picture frame may be accur- 
ately mapped. This procedure also permits an accurate determina- 
tion of the scale factor between the final TV photograph and the 
target plate. 
Furthermore, the reseau grid enables the use of the 
goniometer principle to calibrate the internal geometry of the 
optical lens system. 
This paper describes a group of experiments conducted to 
measure the magnitude and pattern of geometric distortions in TV 
systems and to determine the expected accuracy of this two-stage 
calibration procedure. 
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