Techniques for Conducting Comparative 
Tests of Restitution Instruments 
by S. A. HEMPENIUS, B. MAKAROVIC, A. J. VAN DER WEELE 
I.T.C., Delft 
I. Introduction 
1.1. The present paper has been initiated during the meeting of Comm. II, III and IV 
of the ISP at Milan in 1962. The availability of a large collection of various types of 
instruments at the ITC was perhaps the reason to invite the Dean of this institutet to 
prepare a paper. During this meeting the scope of the paper was discussed in only a very 
general way. After this conference the president of Comm. II, suggested to produce an 
invited paper which would enable the readers to derive from it a comparison between 
photogrammetric instruments. In a correspondence between the Dean and President 
Nowicki, it was made clear that it is impossible to an institute like the ITC to enter into 
such evaluation of instruments which not only endangers the neutral stand of this in 
stitute, but would also be of very little use to the users, because the evaluation of the 
qualities of instruments requires so many different viewpoints, sometimes of a local 
nature, that a general classification of instruments in many cases would be misleading. 
The counterproposal was that the staff of the ITC would make a number of remarks 
about the testing of instruments. Even for this the reader should realize that they take 
into account only a limited number of viewpoints. 
The main result deals with precision of the operation and with the accuracy of the 
instrument. Furthermore we find with repetition of the same tests some data about the 
stability of an instrument and the resistance against wear. 
Such constant factors, however, such as for instance, the flexibility for dealing with, 
different types of photographs, the ease of handling the instruments, requirements for 
training of operators, the economy of its use based on the cost of the equipment and the 
productivity, the expected period for amortisation, requirements for instalment of the 
instrument will regard to air conditioning, vibrations, etc. are not included in the usual 
methods of evaluating but are nevertheless of great importance for the choice of a certain 
type of instrument. In addition to all this it may be that even the fact whether more 
instruments of the same make are used in a country, and the possibility for cheap servi 
cing by the factory is of importance. This shows how useless it would be to try to compile 
a list with evaluations of each type. Even a complete enumeration of all criteria for this 
evaluation will always be incomplete for complicated plotting systems and will never 
take into account a number of these local considerations which are decisive in some cases 
for the choice. *) 
Limiting ourselves in this paper to methods of testing of instruments we should 
distinguish between: 
1. the geometrical performance which in regular practice is derived from 
a grid measurement 
2. the optical performance to which the normal user generally pays very 
little attention and which is mostly accepted as it is 
3. the dynamic performance of the instruments. This deals with the con 
formity in details between negative and map after transfer of straight 
and curved-lines. 
i) An example of a complete enumeration of criteria for such a purpose is given in 
[1] for stereoscopes. A similar set-up for restitution instruments in general would be 
several times more extensive.