136 THE DESIGN OF PHOTOGRAMMETRIC PLOTTERS, DISCUSSION 
action of the large pattern. Also the rapidity and 
accuracy with which orientation cycles can be 
performed favours the use of more cycles and 
shows a more complete clearance of the Y 
parallax. The stereomat can be applied to exist- 
ing plotting instruments, but the speed and accu- 
racy of the resulting operation is limited by the 
optical and mechanical limitation of the instru- 
ment chosen. Optical aperture is the fundamen- 
tal factor affecting stereomat performance and 
is the principal limitation governing its function 
with plotters. Inertia governs the size and com- 
plexity of the mechanism required to move the 
carriage and floating mark assemblies. Also the 
acceleration forces during fast plotting are a 
function of the inertia and these functions may 
disturb and reduce matching adjustments. Model 
size is the most serious factor affecting inertia 
since it determines the size and weight of the 
carriage assembly and also the distance it moves. 
Inertia varies between a third and a fifth power 
of the model size. The Helava plotter seems to 
be an ideal basis for the automatic stereo in- 
strument. The overall construction permits large 
apertures to be employed and plotting is at 
photo scale. The mechanical construction can be 
light and rigid and various control adjustments 
were not subject to disturbing effects of machine 
vibrations and stress. 
Mr U. V. Herava: I would now like to call 
on Mr Blachut to speak on the use of this new 
type of instrument. 
Mr T. J. BLacHuT: Speculation on the use of 
the roll end on the scope of a piece of equipment 
that is not yet built is always connected with 
certain risks. The risk is still greater if there is 
little experience on which to base such specula- 
tion, since the instrument as it is the case is 
based on new principles and presents a complete 
departure from the familiar technique. How- 
ever, we are discussing now this particular sub- 
ject and I do not see any reason why we should 
not be permitted to perform such a speculation. 
First of all, I am thinking that we should 
refer to a family of the instrument and not to 
one single piece of equipment. As far as analyt- 
ical plotters are concerned, the different orders 
of plotters could be derived by a simplification 
and not by a basic change in the design of the 
equipment. That is quite a fundamental differ- 
ence with the conventional type of plotters in 
which, as you know, each plotter of a different 
order is altogether an entirely different instru- 
ment. That, of course, will have important 
practical implications on the operational work; 
it will lead to the unification which is a most 
desirable feature and also it will lead to simpli- 
fication and unification of the operations. 
Another very important characteristic feature 
of the family of instruments which are called 
analytical plotters will be flexibility in intro- 
ducing and using different photographic material 
and in the introduction of various corrections. 
At the present time it is planned to build into 
the computor corrections for earth curvature, 
for distortion, for atmospheric refraction, for 
film shrinkage and for other corrections; in 
particular, I have in mind the corrections which 
we call global corrections, which will be empiri- 
cal corrections, including all possible constant 
errors involved in the photogrammetric opera- 
tion, even if they are not symmetrical, but which 
could be built in such a future plotter. 
Maybe less obvious but not less important 
are probable changes that may be brought about 
by the fact that the relative and absolute orienta- 
tion of any stereomodel can be stored within 
the observation accuracy by simply setting 
orientation elements on the plotter; it is some- 
thing which Mr Helava mentioned in his talk. 
There is not too much time to elaborate on it, 
but it appears that in future it may be possible to 
use directly the elements of orientation on the 
instrument and even to do away with ground 
control points. 
[ think if you would like to express in a few 
words the most important characteristic of this 
type of plotter then we would agree that the 
flexibility in introducing all sorts of corrections 
is probably the most important and most 
characteristic feature which should lead in 
future to the ultimate accuracy in photogram- 
metric mapping. 
All in all, plotting instruments based on 
numerical methods are new factors, not only 
from a purely instrumental point of view but 
also from the point of view of practical opera- 
tions. Conventional plotters which are often 
wonders of mechanical perfections have reached 
the limit of their performance because of the 
limitation in the physical projection system on 
which they are based, and not so much because 
they are not accurate. If we intend to advance 
the photogrammetric techniques beyond the 
limits of the tools used at present we must design 
instruments not only better qualitatively but 
more efficient because of their principle. 
The PRESIDENT: I am afraid time is up and at 
this time of the day there is no place for discus- 
sion. 
The meeting was continued later in another 
room, under chairmanship of Mr Helava, but no 
adequate record of the discussion is available 
for publication. 
  
8