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BALLISTIC PHOTOGRAMMETRY, SCHMID 37 
the corresponding geodetie techniques of measuring angles and directions for the similar 
purpose, intersection photogrammetry either determines the spatial position of a point by 
triangulating corresponding rays, originating from two or more stations, or the spatial 
position and orientation of a specific camera is determined by the method of resection in 
space, whereby the double and multiple point resections occupy a place of special interest, 
insofar as they represent the geometrical concepts on which the single model, the strip 
and the block triangulations, are based. 
The historical development of photogrammetry does not reflect these geometrical 
fundamentals. The phase of Intersection Photogrammetry was succeeded by the concept 
of Stereophotogrammetry, comprising the methods and techniques which presently dom- 
inate the applieation of photogrammetry in the topographie field. As a matter of fact, 
the purist in stereophotogrammetry often considers it beneath his dignity to pay much 
attention to the outmoded concept of intersection photogrammetry. This situation prevails 
despite the fact that the stereo-effect in photogrammetry is of basic significance only in 
dealing with the problem of measuring or plotting spatial curves (e.g. contour lines) on 
a stereoscopic model, after it has been re-established. From a geometrical standpoint, the 
stereo-effect contributes nothing during the process of restitution which is undoubtedly 
the more important phase, concerned with the re-establishment of the orientations of the 
photographs by the methods of relative and absolute orientation. The well known geo- 
metrical theorem for the relative orientation demands that five pairs of corresponding 
rays of any two associated photogrammetric bundles be intersected. The absolute orien- 
tation has its equivalent in a three dimensional coordinate transformation. 
Aside from considerations dealing with precision and economy, the restitution of the 
orientations of a pair of photographs can be performed by alternately observing first 
one and then the other of the two photographs. Analytically speaking, the orientations 
can be computed from a certain number of plate coordinate measurements, observed on 
a monocular comparator independently, for each of the photographs under consideration. 
Qualitatively speaking, the stereoscopic principle becomes significant during the 
process of restitution, only with respect to identification. Quantitatively speaking, the 
stereoscopic effect increases the metric precision of the measuring operation. 
There is no reason to assume that any specific application of photogrammetry can 
monopolize these advantages. The field of non-topographic applications, usually signi- 
fying the domain of Intersection Photogrammetry, definitely will not forego the possi- 
bility of applying the stereoscopic observation method. 
Finally, there are problems in the field of non-topographic application which demand 
the method of stereoscopic evaluation of the model, once established. For instance, photo- 
grammetry is used for the study of cloud formations and for the related problem of 
determining wind vectors at great heights by photographing sequences of smoke puffs 
or vapor trails, as associated with most missile firings. For reason of identification the 
evaluation can only be performed by using three dimensional restitution equipment, in 
the same way as these simulators are used in most topographic mapping projects. 
The purpose of this introduction is to show that the photogrammetric method as ap- 
plied in the non-topographic field and specifically in the field of Ballistic Photogram- 
metry is, with respect to the basic geometrical principles, not merely related, but actually 
identical with its counterpart in topographic application. Accordingly, the requirements 
on field instrumentation, data reduction methods and equipment are similar. 
As a matter of fact, the wide variety of problems encountered in the non-topographic 
field calls for such flexibility of the measuring method, that nothing short of a solution 
of maximum generality will do. 
The rigorous request for significance of the results, in terms of X,Y, Z-coordinates 
and in terms of corresponding rotational parameters, eliminates any compromise with 
regard to rigorous geometry. The use of the photogrammetric camera as a device for