ANALYTICAL PHOTOGRAMMETRIC INSTRUMENTS 
2 
dependently given control data, a method 
that is justifiable as long as one recognizes 
that the pseudo-svstematic accumulation of 
random errors is not improved by such tech 
niques. 
Accepting the weakness of any generaliza 
tion, it is possible, therefore, to say that the 
present generation of photogrammetric, 
analogue, data-reduction equipment is ad 
equate for the photogrammetric data evalua 
tion process, as long as the photogrammetric 
record (the photograph) is considered as a 
more or less true central perspective, affected 
only by random errors or by a population of 
systematic errors of about equal magnitude 
which, when acting jointly, compensate 
partly for each other and which, in accordance 
with the central limit theorem, can be ad 
justed together with the normally distributed 
measuring errors by applying data evaluation 
techniques which are based on—or which are 
sufficiently close to—the principle of least 
squares. 
The potential of the present analogue ap 
proach is further enhanced because the data 
evaluation process is intuitive and can in 
general, be executed by men less skilled than 
those needed to perform an equivalent, 
strictly numerical data evaluation. 
This statement is not meant to contradict 
the well-established fact that the measuring 
process on a comparator-type instrument is 
simpler and can, therefore, be accomplished 
by less-skilled manpower. However, prac 
tical experience has shown that the handling 
of large amounts of data by strictly numer 
ical evaluation principles demands a higher 
level of organization within an agency and 
more highly skilled manpower to supervise 
production and analyze results for statistical 
significance. 
Therefore, the conclusion can be drawn, 
supported by the results of routine work, that 
the new field of analytical photogrammetry 
does not offer significant advantages in terms 
of the accuracy of the end product, as long as 
the previously stated assumptions concerning 
bias errors in the photographic record hold, 
and as long as the accuracy requirements are 
not in excess of the aforementioned error 
bounds. The question of economy is another 
matter which will be considered later. 
An equally valid conclusion is that the 
analogue approach cannot be expected to be 
capable of a significant increase in accuracy, 
mainly because any significant improvement 
of the accuracy of the photogrammetric 
measuring method can only be obtained by 
acknowledging the fact that the principle of 
central perspective is only a first approxima 
tion. Deviations of a systematic nature, 
which are not consistent with the concept of 
central perspective, are caused by specific 
physical conditions of the atmosphere at the 
moment of exposure and by physical and 
chemical influences which affect the process 
of taking the photographs. 
The most obvious bias errors are those in 
troduced by the influences of asymmetrical 
radial and (the so improperly named) tan 
gential distortion. Furthermore, there are in 
fluences affecting, in a systematic way, the 
dimensional stability of the emulsion carrier 
as a whole, as distinguished from random 
emulsion shifts. And, very significant, there 
are changes in the calibrated elements of in 
terior orientation brought about by the in 
stantaneous environmental conditions pre 
vailing at the time of exposure. 
An important consideration in the area of 
photogrammetric data acquisition is the trend 
towards the use of panoramic cameras. In 
such systems, the concept of central perspec 
tive is purposely sacrificed for longer focal 
lengths and the higher resolutions which are 
possible with the typically narrow lens open 
ing angles. The economically attractive and 
technically feasible possibility of a further 
increase in flying height will, through the use 
of these dynamic data acquisition systems, 
provide means to acquire supplementary 
photography with scales and resolutions 
that are not obtainable with conventional 
wide-angle photographic systems. Particu 
larly promising is the application of photo 
metric methods to photography taken from 
satellites for such purposes as lunar mapping. 
The removal of dynamic distortions in the 
corresponding raw material cannot readily be 
accomplished with analogue equipment; and 
certainly not to the degree necessary to pro 
duce an undistorted photograph which is 
sufficiently compatible with the principle of 
central perspective so as to be suitable for use 
in classic restitution equipment. 
Finally, it is necessary to be aware that the 
family of sensors available for the execution 
of three-dimensional triangulation has al 
ready been broadened and will continue to 
grow. Not only photography that deviates