Mr. Blachut answers that the precision that can be obtained for the measurements should not 
be rejected. There exist numerous sources of errors and one should eliminate as many of them 
as possible. 
Mr. Thompson concludes from the results obtained by Mr. Schut, that the analytical method 
is valuable. He agrees with Mr. Blachut with respect to the precision of the measuring instrument. 
Mr. Dowson (Great Britain) says the following: On the Ordnance Survey of Gt. Britain we 
have developed and used an analytical method of aerial triangulation for several years past, for 
mapping on scales of 1:10 000 and larger, using the Cambridge Stereocomparator and the electronic 
computing machine at the National Physical Laboratory. We now not only compute the relative 
orientation but also form strips by this means. Attracted by the economy of film photography 
compared with glass plates, we devised a reseau to control the distortions in the pictures. The 
reseau also provides a useful reference system on the photograph, it furnishes an abundance of 
suitable pass points, and it also makes it possible to use a relatively simple measuring instrument. 
Some advantages of the analytical method compared with the plotting machine are: It is simple 
to allocate the work to many different observers; it is possible to exercise a valuable statistical 
control of accuracy at different stages; and it is possible to employ less skilled operators. We still 
require: still better film cameras incorporating a reseau; a better, self-recording stereocomparator; 
and further developments in the computing. We believe there is more scope for the development 
of the analytical technique than in the plotting machine method. 
Le président donne ensuite la parole à M. U. Bartorelli (Italie) dont la com 
munication est intitulée: »An Analytical Method of Aerial Triangulation». 
Résumé: 
The Author proposes to chain every i -f-1 photogram (to the i photogram 
already absolutely orientated) considering only the four directions, of said 
photogram, departing from its view point and passing through the two already 
determined pass points, which are common to the photograms i — 1, i, 
and the two unknown points, common to i, i -j- 1, i + 2. 
The tetrahedron, of said four directions, (whose faces are known from the 
measurements made on the photograms) assumes its absolute orientation, 
subjecting two of its edges to belong to the two already determined pass points, 
and subjecting the other two edges to be coplanary with the two already 
determined directions, departing from the view point of the preceding i photo 
gram and passing through the two still unknown pass points. In this manner the 
i -f- 1 view point as well as the two new pass points are determined, thereby 
obtaining the elements needed to chain the subsequent i -f- 2 photogram by 
adopting the same procedure. 
Each chaining consists of the following operations: 
U. Bartorelli: An 
Analytical Method of 
Aerial Triangulation. 
(Publ. Ill B 4) 
1) measuring, on each photogram, of the image coordinates (cartesian or 
polar) of the six chainingspass points (four at the vertexes of each photo 
gram and two at the median points of the sides in the direction of the 
chain); 
2) calculation of the cosines tetrahedrons faces to be considered, by means of 
the knowledge of the coordinates measured, and of the focal distance, and 
of the distortion of the take camera; 
3) for each photogram, in its order, calculation of the three coordinates of the 
vertex of each tetrahedron and of the twelve director cosines of its edges. 
These fifteen unknown quantities are calculated by solving a system of 
fifteen equations, each of second degree, inasmuch as there is known the 
coordinates of the view point and these of the two pass points determined 
by the chaining of the preceding photogram, and the director cosines of the 
exiting directions of that view point passing through the two pass points to 
be determined. This equation system is solved by iteration, quite rapidly, 
by using electronic computing machines; 
4) calculation of the coordinates of the two new pass points by means of direct 
intersection from the view points of photograms i and i + 1- 
The principal advantages of this system compared to any other analytical 
method are the following: 
245