he distance 4 of 
two crests p are 
the measurement 
determine T by 
still, by counting 
d near the shore. 
ible to determine 
S. 
hunder centres 
| speed of cer- 
in region several 
| turns up, photo- 
‚ed in relation to 
g is made accor- 
btained the plani- 
ing the operation 
ve objectives of 9 
ly used. For very 
metimes polarized 
as a knowledge of 
eters is sufficient. 
d in particular to 
ers on the level 
vith the aid of 
"Electricité de 
he Mont Blanc, 
eport of it will 
yn photographs 
, the movement 
ribution of the 
galaxies etc. 
d today, which 
juantities, such 
per movements 
otographs. The 
congress in the 
en is found in its 
ethods are used. 
15 
(a) Control of close-up cameras and plotting instruments. 
To be able to check the instruments successively a test-field was arranged, where a 
number of points carefully determined as to their position, were reproduced in the 
cameras and then plotted in the instruments. The problem of getting a sufficient number 
of carefully determined points, suitably dispersed in space, was solved by the aid of 
measuring tapes, suspended from the ceiling of a large room. On the tapes a sufficient 
number of markings, indicated by suitable signals, served as proper points of control. The 
tapes were kept straight by weights, hanging in water. By this arrangement vibrations 
were subdued and the tapes were practically immobile. The position of the tapes was 
determined by intersection from three points on a base. The position of the signals on 
the tapes was controlled by vertical angle measurements. The position of the camera was 
determined from the permanently marked basepoints. From successive pictures taken of 
the points of control, their position could be reconstructed in a stereocomparator or other 
stereoscopic instrument. By this means an accurate control of the function and precision 
of the camera and instrument was obtained. These operations had to be made at regular 
intervals. 
(b) Multiplex in close-up photogrammetry. 
Multiplex was used for both photographing and plotting of objects of a suitable 
size. Certain advantages were thereby obtained as e.g. the principle of Porro-Koppe could 
be rigorously observed. 
(c) Measurements of mobile objects. 
In order to determine the character of slow movements, e.g. currents in lakes and in 
the sea, floats with deep-reaching crosses were used, which followed the current. The floats 
carried small electric lamps with batteries. Photographs were taken by night with 
stereoscopic cameras, the shutters of which were opened and shut at regular intervals. 
Two successive pictures consequently gave complete information of the speed and direc- 
tion of the current at fairly simple plotting. 
At more rapid movements, e.g. pouring gas or parts of the body in motion, considerable 
difficulties arose with reference to synchronizing the shutters with sufficient accuracy. 
Special procedures were used for this, which ought to find considerable employment. 
The points to be measured were signalled by flashing lamps. To study the movement of 
the foot at a normal walk, for example, small electric lamps were placed on heel and 
toe. The lamps were made to flash simultaneously but with varying intervals of time. 
The person was then made to walk in front of an open stereoscopic camera with a base of 
120 cm. The movements of the foot could be reconstructed in detail from the pictures 
with the aid of stereoscopical measurements. For similar purposes stroboscopes were used. 
(d) Medicine. 
Problem: Measuring the thickness of fingers before and after certain injections. 
Procedure: The fingers were simultaneously stereo-photographed from both sides. The 
thickness (diameter) of the object was computed from measurements in a stereocompara- 
tor (Pulfrich). The ends of the diameter were identified through stereoscopic viewing of 
Successive plates. 
Result: Optimal precision about 0,1 mm (mean error). Expected behavior of the thick- 
ness in question. 
(e) Odontology: 
1. To be studied: Volume and behavior of swelling of patients face due to surgical 
treatment (generally extracted teeth). 
Procedure: Contour lines were drawn in a stereoinstrument. Part of the face was mar- 
ked out once and for all in the instrument, to the automatic drawing device of which was 
coupled a planimeter. The planimeter arm was regulated so as to ensure the reading of 
the volume from the planimeter scale. A reproducible absolute orientation is a necessary 
condition. The best way of obtaining this was to make the patient bite at an impression 
compound. 
Result: Optimal precision about 2 cm? (mean error). 
2. Work with X-ray stereoscopic pictures. 
Procedure: A device was made to ensure a stable inner orientation of intra oral X-ray 
pictures. It was also made applicable to exira oral pictures. The stereoinstrument (A 6) 
was modified to allow continuous adjustment of the inner orientation in order to facili- 
tate the work with X-ray pictures. The surface of the object was made visible by painting 
on it a net of absorbing (heavy) matter. : 
3. Determination of the form of the prothetic base. 
Procedure: Photogrammetric methods have been used for similar purposes, but, it may 
be found advantageous not to pursue this course. Form lines can be drawn directly from 
a chalk model, by using a stereoscopic microscope connected to a plotting device. |