Hempenius, Makarovic, Van der Weele, Tests of Restitution Instruments 
From these three problems the first, dealing with grid measurements, is treated in 
many publications. Consequently in this paper only a number of general remarks about 
this will be made. 
Originally the ITC staff had the intention to also publish in this paper the test for 
the evaluation of the optical qualities of different instruments. At the present stage this 
could only be rather superficial and will perhaps be the subject of a later ITC Publication. 
Special attention will be paid to the dynamic performance which is perhaps a new 
chapter in the subject of testing plotting machines. 
Consequently it is obvious that this paper is far from complete and has not the 
pretention to cover the subject of methods of completely testing plotting machines. 
In the next paragraphs of this chapter a few more remarks of a general character 
will be made, mainly by raising questions without trying to answer them all. 
I. 2. Not entering into the choice for purchasing new instruments, but considering the 
questions related to instruments that are already available in a photogrammetric 
organisation, we see in general two groups of questions: 
1. How is the quality of the instrument changing (generally decreasing) as a function 
of its age? 
The answer to this question will be required to decide: 
a. whether a new adjustment of the instrument has to be undertaken. 
b. whether parts of the instrument have to be replaced or repaired. 
c. whether the whole instrument has to be replaced, 
etc. 
2. Has a given instrument sufficient capacities to be used for the solution of problems, 
for which it has not been primarily designed. 
The answer to this question is obviously important when deciding whether new in 
struments are required for a new task, or whether existing equipment can fulfill the 
role. The same question has, at least in theory, been put and been answered in a 
positive sense with respect to the task for which the instruments have been bought 
originally. 
The two groups of questions, mentioned above, can be answered in principle by the 
application of the same test procedure. There may, however, be a difference in the or 
ganisation of these tests e.g. in relation to its purpose, to the time available and conse 
quently in relation to the number and type of measurements used in each case. For the 
description of possible tests contained in the following sections, we will make no distinc 
tion of different possibilities on this basis since we feel that the decision should be left 
to responsible authority, taking into account the circumstances and requirements for 
each particular case. 
Neither do we attempt to propose ‘standard’ procedures for testing, since we feel 
that a ‘standard’ procedure, applicable to all instruments under all circumstances and 
still giving results that are comparable, does not exist. 
I. 3. The modern development of instruments shows an increasing application of electri 
cal elements to replace mechanical and optical parts, and a tendency to use digital 
computers instead of mechanical or optical solutions of the resection and intersection 
— problems involved in the reconstruction of terrain-models from aerial photographs. 
A core of new problems arises with the application of radar and television techniques 
to replace photography, but also by the use of electronic scanning instead of the human 
observer. 
Each of these new features has been realised already in one form or the other and 
although they may still be in an experimental stage at present, it may be expected that