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168 
E. Thompson: The 
Tompson-Watts plotter. 
В. Hattert: International 
Comparative tests 
— a suggestion. 
(Pubi. II H 10) 
The distortion correcting devices equipment can be simplified by using eccentric cams and 
varying their eccentricity by calibrated thicknesses. Principal distance variations in function of {}, 
caused by an eccentricity e of a spherical cam, are given by: 
df’ = e (1 — cos /?) 
E and F expression and e value can be determined, in the field of the troposphere, by the least 
squares method. The possible corrections have been checked comparing them with the theoretical 
values computed by A. Leijonhufvud (Photogrammetria — IX — 3 — pages 93 seq.) — Practical 
tests confirm theoretical researches. 
La parole est donnée à M. E. Thompson, Grande Bretagne. Il présente sa 
communication »The Thompson-Watts plotter». Résumé: 
The paper draws attention to the special features that distinguish this new 
instrument from existing plotting instruments, both from the constructional 
as well as from the user’s point of view. 
The main features are, firstly, a design in which the formation of the space 
model is completely independent of the plotting mechanism proper. This has 
important repercussions on the effective accuracy of the instrument as well as 
on the facility for achieving absolute orientation without disturbing relative 
orientation. Secondly, a link mechanism that allows the scanning movements 
to be shared between observing telescopes and cameras, resulting in a remarka 
bly compact design and simple optical system. Thirdly, a special arrangement 
of rotation axes to facilitate aerial triangulation. 
In addition to these, the instrument incorporates several minor features that 
are of considerable value to the user. In particular it possesses a variable 
magnification system that not only equalizes the magnification in the two 
halves of the binocular system, but allows a choice of a wide range of magnifica 
tions continuously and without changing lenses at any time. A unique feature 
is the incorporation for use during setting, of a fast movement in the Y- 
direction controlled by the Y-handwheel. 
It is the only existing instrument, as far as is known, that will allow the use 
of normal angle pictures covering the popular 9 inch X 9 inch format; that 
is to say pictures taken with a camera of principal distance 12 inches. The 
interchange of cameras of 12- and 6-inch principal distances is extremely 
simple and can be carried out without disturbing in any way the camera 
calibrations. 
The instrument should be of special interest to photogrammetrists in that 
it is the first precision instrument to be built on entirely original principles for 
at least 25 years. 
L’appareil de restitution Thompson-Watts 
Le nouvel appareil de restitution Thompson-Watts fait partie du groupe Porro-Koppe. La 
construction en est basée pourtant sur des principes entièrement nouveaux en ce qui concerne la 
formation de l’image plastique et la matérialisation de celle-ci dans l’espace. En effet, cette 
formation ne dépend nullement du dispositif de restitution proprement dit, ce qui permet dans la 
construction de l’appareil un moindre degré de précision par rapport à l’efficience prévue. En 
outre, grâce à un dispositif spécial, facile à construire et à mettre au point, le mouvement dans 
l’espace du point matérialisé se décompose en un mouvement dans chacun des deux plans XZ, YZ. 
Il en résulte un appareil à dimensions particulièrement réduites et un système d’optique relative 
ment simple. 
M. B. Hallert, Suède, présente un exposé sur »International Comparative 
tests — a suggestion». Résumé: 
Up to now mainly the final results of the entire photogrammetric procedure 
have been tested. For the judgement of such results, however, it seems very 
desirable that also the fundamental operations of the normal photogrammetric 
procedure are individually tested. The systematic and accidental errors and the 
discrepancies in the conditions of the fundamental operations are evidently the