64 — 
BEARINGS OF THE DESIGN OF PHOTOGRAMMETRIC PLOTTING 
INSTRUMENTS 
The lecturer takes into consideration the requirements to which a plotting 
instrument must satisfy both under the economical and technical points of 
view, in order to point out how many and what are the advisable solutions. 
6°) PAYS-BAS 
a) SOME NEW ASPECTS IN STEREOSCOPIC VISION, by C.A.J. 
von Frijtag Drabbe. 
(SUMMARY OF A DESCRIPTION THAT WILL BE PUBLISHED 
IN « PHOTOGRAMMETRIA »). 
The vriter discusses nonocular vision or vision with one eye and the 
relation between the object and the image we get of that object. Is the 
image we form of an object really that object, that is to say, do we optically 
observe the object itself or not ? 
He also discusses binocular vision or vision with two eyes. When Vve 
look again at the object which we observed with one eye before, it is nemely 
evident that both eyes are directed at the same time at the same object and 
even at the same spot of the object (convergence of the eye-axes at that 
point). Is convergence a partly acquired thing ? Experiments show that 
convergence is not acquired and that the feeling of convergence will not be 
decisive for estimating distances. The conclusion of these experiments is that 
we might deduce that convergence of the eyes is an inborn property, connec 
ted with « viewing » or « focusing » at something. 
Also is discussed the influence of binocular vision on the forming of a 
stereoscopic image. One is able to get a stereoscopic image of a stereo couple 
by staring or squinting. Without solving the problem how we get a double 
image we are sure that when looking at an object that is not lying near 
intersection of the eye-axes, we always observe a double image of that 
object, whe ther we stare or squint. So, if the object is a stereo couple, we' 
see four images. With the help of our brain we make a reconstruction of two 
of these images and the result is that we « see » a three-dimensional object 
by using the parallaxes. 
Another subject is the printing of a stereocouple by applying vecto- 
graphes (polarisation manner), printing in red and blue and looking with 
adapted eye-glasses (filters) to get the right stereoscopic image. 
When looking without a stereoscopic it is not difficult to understand 
taht we have the capacity of joining two stereo photos ans getting a three 
dimensional reconstruction as if we looked normally.