developed. A block of photographs is divided into strips, the strips into 
models and each model is solved in two steps, relative and absolute 
orientation. 
The first application of the electronic computer to photogrammetry 
was perhaps in the form of the adjustment of instrumentally triangulated 
strips analytically, rather than graphically. Then, with the ever- 
increasing availability of the computer and its continuous improvement, the 
possibility of an all-analytical photogrammetric triangulation evolved. 
However, the majority of the analytical methods developed represent nothing 
but mathematical formulations of the respective analogue techniques. 
Individual stereo-pairs are relatively oriented, then attached to one 
another to form strips. The strips are adjusted to ground systems using 
mathematical formulae representing the old graphical techniques. In the 
more recent developments, strips are adjusted to one another to form a 
block which is in turn adjusted to control. Thus, it becomes evident that 
the current methods in analytical photogrammetry are based upon concepts 
and definitions that were originally set for conventional and analogue 
methods. One may then raise the question: Could there be other concepts 
that are more suitable for analytical photogrammetry? 
In the author*s opinion, the single photograph, and not the 
stereo-pair, is the proper basic unit for analytical photogrammetry. The 
geometry and analytical relationships of the bundle of rays projecting 
perspectively a piece of terrain on an aerial photograph are the same for 
all photographs. The orientation elements at the moment of exposure of 
one photograph are entirely independent from those of another. 
In a purely analytical approach, it is obvious that all photo 
graphs contribute equally to the solution. Consequently, there should be 
no need to adhere to the classical practice of unequal forward and side- 
lap, which would favor one direction in the block over the other. An 
equal all-around overlap, on the other hand, would be more appropriate for 
analytical photogrammetry, since it secures geometric harmony and homo 
geneous strength. With 2/3 overlap and side-lap the strength of the 
geometric configuration of the bundles of rays in a block of photographs 
would be great indeed. 
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