5. TESTS OF THE STEREOSCOPIC ACUITY OF OPERATORS 
Because of the great importance of the quality of the 
operator in the photogrammetric procedure it would be 
of value to find simple and reliable methods for numerical 
determinations of well defined personal properties. Among 
such properties is the stereoscopic acuity. There are several 
well known devices and methods in practical use for such 
purpose (test tables of various kinds, three — rods test, 
etc.), e.g. Ref. 5.1: 4—5. 
In order to test the stereoscopic acuity continuously 
during arbitrary periods, also in connection with ordinary 
work in stereoscopic plotters, Dr. med. T. Krakau has 
constructed a device, founded upon the three-rods prin 
ciple and equipped with arrangements for automatic 
registration of the results of the tests, Ref. 5: 1 and 5: 2. 
This device has been used in experiments with well 
trained stereo-operators in order to determine representa 
tive numerical data as “standard” for the comparison with 
arbitrary people to be tested. 
The device is doubtless very promising for the purposes 
mentioned. Careful calibrations of the device itself, and of 
the oscilloscope are necessary. 
An interesting investigation of visual factors affecting 
the quality of photogrammetric coordinate measurement 
has been made by Dr. D. C. O’Connor, see Ref. 5.1: 6. 
References: 
5.1: 1 Krakau, C. E. T. An Automatic Apparatus for Time 
Series Analysis of Visual Acuity. Vision Review Vol. 
7, pp. 99—105, 1967. 
5.1: 2 Krakau, C. E. T. En metod for fortlopande provning 
av stereosynskarpan. Forsvarsmedicin 3, pp. 27—35, 
1967 (A Method for the Continuous Testing of Vi 
sion and some Viewpoints Regarding the Testing of 
Personnel Engaged in Stereometric Assignments). 
A method is described for automatic, continuous 
testing of the stereo-acuity of vision. On the basis 
of some preliminary trials, factors having an effect 
on stereovision are discussed. When developing a 
suitable procedure for testing personnel engaged in 
measurement recordings based on stereoscopic 
vision, it would appear to be essential to take into 
account time-dependent parameters (time of training, 
the duration of the test, times of reaction and ex 
posure). The apparatus described enables stereo 
acuity to be determined taking factors such as these 
into account. 
5.1: 3 Krakau, C. E. T. A Device for the Automatic, Con 
tinuous Testing of Stereoscopic Acuity. Manuscript. 
5.1: 4 Howard, H. J. A Test for the Judgement of Distances. 
American Journal of Ophthalmol. 1919 (2). 
5.1: 5 Zorn, H. C. An Instrument for Testing Stereoscopic 
Acuity. Photogrammetria 1965: 6 December. 
5.1: 6 O'Connor, D. C. Visual Factors Affecting the Preci 
sion of Coordinate Measurement in Aerotriangula- 
tion. GIMRADA Res. Note No. 21, Fort Belvoir, 
Va 1967. 
6. SUMMARY AND CONCLUSIONS 
The work, the results of which have been presented here, 
has been performed in accordance with the resolutions and 
recommendations of the International Society of Photo- 
grammetry. The general conclusions can be summarized as 
follows. 
1. It is for evident reasons necessary that well defined 
concepts and terms for geometrical quality be used in 
photogrammetry. The presented concepts and terms for 
quality have been accepted by the majority of national 
societies of photogrammetry. 
2. Performed partial and complete calibrations of 
photographs under operational conditions from different 
cameras in aerial and terrestrial photogrammetry have 
proved that significant differences frequently occur in 
comparison with the results from laboratory calibrations. 
Therefore calibrations under operational conditions, in 
addition to laboratory calibration, are recommended. This 
is necessary for the correct reconstruction of bundles of 
rays from photographs. 
3. The technique used for the calibrations makes it 
possible to establish tolerances for the differences of the 
results of calibrations from standard. 
4. The described technique for complete calibrations of 
photographs from close-up cameras and other imaging 
devices has worked satisfactorily and is recommended. 
5. Polyester film base has proved to give considerably 
better quality of image coordinates than acetate film base. 
A certain tendency of lacking orthogonality of image 
coordinates has been found in polyester films, however, 
which should be carefully noted and further studied. 
6. Partial and complete calibrations of projectors of 
analogue restitution instruments have proved that signif 
icant differences from standard frequently occur. The 
technique used makes it possible to establish tolerances 
for such differences. For the correct reconstruction of 
bundles of rays, the photographs must be calibrated ac 
cording to point 2. above. 
7. It seems possible to use the basic accuracy of projector