TARGET RANGES FOR CALIBRATION OF CLOSE RANGE CAMERAS 
Torlegard (1967) provides the development of a method of calibration of close 
range cameras from reduction of exposures of suitably constructed, three dimensional 
target ranges. He also provides specific results from a particular range comprised of 
a steel framework 3.6 m wide by 2.4 m high and 2.8 m deep on which a total of 177 
targets are supported. The coordinates of the targets were established by triangu- 
lation with a Wild T3 theodolite to an estimated rms accuracy of 0.07mm. The 
method employed by Torlegard for the photogrammetric calibration is equivalent to 
the special case of Aerial SMAC in which only a single frame is reduced (hence, the 
need for such a large number of targets). As in the original development of Aerial 
SMAC, Torlegard's method does not take into account the variation of distortion with- 
in the photographic field (i.e., distortion at midfield is assumed to hold throughout 
the field). 
The major problem associated with the three dimensional target range method 
lies in the practical difficulties associated with constructing, surveying and maintain- 
ing the range. Because of SMAC's sufficiency with a small set of targets, this problem 
is alleviated to a considerable degree by the exercise of SMAC (properly modified to 
account for variation of distortion within the photographic field). Of even greater 
significance is the fact that SMAC opens up the possibility of employing a two 
dimensional target range to effect a full calibration of the inner cone. Such a range 
has been constructed at DBA Systems. It consists of a black-painted horizontal slab 
of concrete, 5 by 5 meters square by 0.3m thick, onto the surface of which a total 
of 650 targets have been attached. The targeting density of about 25 targets/square 
meter is sufficient to permit sections as small as one half square meter to be exercised 
effectively in a SMAC calibration. The process used for determination of target 
locations will be considered later; for the present discussion we shall assume the 
locations to have been pre-established. 
The basic requirements for a complete and satisfactory calibration by means 
of Aerial SMAC in conjunction with a sufficiently accurate and sufficiently dense 
two dimensional target range are that: 
the formulation takes into account the variation of distortion within the 
photographic field according to the model presented in this paper; 
a minimum of two frames are exposed and reduced; 
at least two of the frames are taken with camera axis inclined at moderate 
angles, preferably about 45*, to the normal to the target array; 
the swing angles of at least two of the exposures differ substantially 
(e.g., X &0* and x«90*). 
When these conditions are met, a sharp recovery can be expected not only for the 
coefficients of radial and decentering distortion but also for all three elements of 
interior orientation, x, ALE The coordinates X¢ ,YC¢ ,Z¢ of the various exposure 
stations are also accurately recoverable. Hence the solution does not require the 
imposition of a priori constraints on exposure stations, as would have been the case 
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