38 BALLISTIC PHOTOGRAMMETRY, SCHMID 
determining individual orientation parameters, e.g., determination of position and atti- 
tude of an airborne test vehicle by photographing ground control points, asks for the 
knowledge of the metric properties of such a camera. 
Calibration values of the elements of interior orientation and distortion must not 
only be obtained with utmost care, but must be maintained during the measuring opera- 
tion which may take place under quite adverse environmental conditions. 
It seems important to emphasize these facts, in hopes of making it clearer that there 
is sufficient common ground in all fields where photogrammetry is used, for producing 
precise measuring results, to merit serious mutual interest. 
The development of a precision photogrammetric measuring system for the purpose 
of supporting research and development in the missile field, appears to be an exellent 
example for demonstrating the benefit which results from such an effort for the general 
field of photogrammetry. 
This influence, already recognizable and definitely predictable for the near future, 
extends into the three basic disciplines, which may be categorized as: 
1. data reduction techniques and theoretical studies; 
2. data reduction equipment, and 
3. field instrumentation. 
Instead of trying to describe in detail the present status of the development in each 
of the three phases, an effort is made to concentrate on those generalities which appear 
to have the potential of being important to the general field of photogrammetry. 
First à warning: No one should expect any spectecular novelties. Photogrammetry 
is a well studied and thoroughly investigated discipline, with a clearly defined area of 
usefulness. In photogrammetry fortunately there will be no break-throughs. Progress 
in general will be in the form of small improvements, leading either to instrumental 
components more useful for specific tasks, or to more precise results obtained in a more 
economical way. 
The unconventionally large geometrical configuration in the actual measuring set-up 
and the request for maximum accuracy are the principal factors in ballistic applications, 
making it mandatory to consider the method of numerical evaluation. 
This method was formerly discontinued in favor of the three-dimensional restitution 
equipment. The potential inherent in electronic computing calls for reconsideration of 
this approach for general use in photogrammetry. 
Usually à measuring program requires a few fundamental steps in the phase of 
data reduction. Considering the evaluation of any triangulation method, it is practical 
to create first a model which rigorously simulates the idealized concept of the measuring 
method. This phase is generally quite simple and is accomplished strictly within the 
domain of solid geometry. The corresponding algebraic expressions must then be mod- 
ified to take care of the physical entities entering the measuring procedure. They can be 
defined as a set of perturbations acting on the idealized geometrical model. 
If we introduce in the resulting formulas the actually measured quantities and the 
given parameters, if necessary with their proper weighting factors, observational equa- 
tions and corresponding normal equations are obtained. By inversion of such a system, 
the unknowns of the problem are computed within the potential of the method of least 
squares. 
If one adheres strictly to these steps, then no amount of ingenuity will produce a 
more significant result. The problem in designing an optimum data reduction method is 
to arrive at a solution which is practical for the phase of data handling and which, in 
our case, is suited for electronic computing techniques. 
The general analytical solution can be based on a very simple geometrical model. 
This model is suited for all numerical evaluation schemes in photogrammetry. Therefore,