Cue MP OW ME 
A 
RS UE 
  
FEE 
  
  
  
es a EE 
== 
   
126 THE DESIGN OF PHOTOGRAMMETRIC PLOTTERS, HELAVA 
tronic rectifier [9], and the electronic facsimile printer [4] may be cited as examples of 
the electronic and electro-optical data transfer methods. 
The method of transferring data for interpretation depends upon the purpose for 
which the instrument or data processing system is designed. If no advanced automation 
is contemplated, the most economical and reliable data transfer is based on optical meth- 
ods, which are most suitable mainly when a human operator is considered. With pro- 
gressive steps in automation the use of electronic methods becomes indispensable. How- 
ever, it is the opinion of the author that no plotter, however automatic, can be successful 
without a provision for human supervision. This means that the visual image must always 
be available for inspection purposes. It is, of course, entirely possible to achieve this by 
electronic means, using modern high resolution display tubes. 
In some cases straight transferal is not sufficient, because the original image is 
required in a deformed shape. This is obvious when two convergent photographs are 
being observed. Simple optical projection through a lens takes care of this deformation 
quite well. If a telescope stereoscope with frontal viewing of photographs is used, ad- 
ditional optical devices are needed to compensate for the difference in shape of homo- 
logous details. The same may be accomplished in a more versatile manner, using a closed 
loop television principle with additional circuits for topological transformations [8]. The 
versatility of this technique makes it possible to extract the required visual information 
from records which bear a poor or nil resemblance to the original object but which are 
created by a process that may be clearly represented mathematically. 
An electronic printer may be used to produce a graphical record of the results of 
the photogrammetric processing. This record is essentially a combination of dimensional 
output data and the information that is of a qualitative nature. It may be established by 
plotting each point on a model according to its correct map position, as a dot of such 
darkness or color as is indicated by the density or colour of the corresponding point on 
the photographs. To show the elevations, additional symbols, such as contour lines or 
tints, may be printed on the same record. For the same purpose it could also be comple- 
mented with a second print on which each point is displaced in the horizontal direction 
by an amount proportional to its elevation. This corresponds to a vertical-convergent 
stereopair, which is made by using an infinite focal length. 
999 
>) 
Parameter transfer. 
Parameters are similar in many respects to the dimensional data discussed above, 
and they may be transferred using the same techniques although there are some impor- 
tant differences. A parameter (not necessarily representing any physical quantity) may 
be a purely mathematical concept and so, may be expressed as a number for the com: 
putation purpose, hence no digitizers are needed. Secondly, the parameters remain con- 
stant during the actual plotting procedure. The transferring problem is, accordingly, less 
demanding than in the case of the continuously varying dimensional data. In addition, 
some of the parameters are, and all of them might be, introduced externally instead of 
being determined during the processing. For these reasons the parameters may be trans- 
ferred in “hard” form, e.g., on punched cards or on punched or magnetic tape. These 
means of transferring the parameters will be of importance for automation of plotting 
machines. 
90 
3.4. Servoing problems. 
3.4.1. Basic servomechanism. 
The use of servomechanisms in a photogrammetric plotter is complicated because 
these mechanisms actually form a part of a process control system. Consequently, we 
must consider not only the positioning servo alone, but also its role in the total solution.