Analytical Plumb Line Calibration 
Simultaneous Calibration and Block Triangulation 
a) Total Overlap of All Photos 
b) Systematic Partial Overlap 
6) Hybrid Methods. 
In the discussions to follow we shall mainly be concerned with general char- 
acteristics of the above approaches. Further details can be obtained from the 
references to be supplied. 
STELLAR CALIBRATION 
The fully analytical stellar approach was first developed in Brown (1956) 
and was extended in Brown (1964), (1965) to consider (a) modeling and recovery 
decentering distortion; (b) recovery of coefficients of atmospheric refraction and 
(c) parameterization of errors in catalogued stellar positions. lt effects the 
simultaneous recovery of the elements of orientation of the camera and the 
coefficients of radial and decentering distortion in a least squares adjustment 
employing the measured plate coordinates of a large number (preferably at least 
200 to 300) of well-distributed stellar images. Properly employed, a stellar 
calibration can lead to distortion functions (radial and decentering) aecurate to 
+1 micrometer or better throughout the photographic format. The stellar reduction 
is also directly applicable to reduction of exposures made on collimator banks, it 
being only necessary to assign appropriate right ascensions and declinations to the 
artificial stars produced by the collimators. The stellar calibration not only yields 
very accurate estimates of distortion for infinity focus, but it also has the ad- 
vantage of yielding accurate estimates of principal distance and coordinates of 
the principal point. For close range photogrammetry distortion at infinity as 
obtained from a stellar calibration can serve as one of the two needed distortion 
functions. 
SMAC CALIBRATIONS 
The stellar calibration just described is performed on measurements of 
images recorded on a single plate over a period during which the camera is assumed 
to be perfectly stable and during which several successive exposures are normally 
made by means of a precisely timed shutter. This process generates a large number 
of well-distributed images from which an optimal selection can be made for men- 
suration. A problem experienced in practice is that, often as not, the assumption 
of camera stability is proven to be unwarranted. This, then, either compromises 
the calibration or else requires the exposure of a fresh plate and a repetition of the 
entire process of mensuration and reduction. Frustration over the frequency of 
such occurrences led us in 1966 to develop and implement Stellar SMAC (Brown, 
1968). In SMAC the assumption of stability of orientation from exposure to