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As far as the development of aerial cameras and the equipment is con-
cerned, K.L.M. Aerial Surveys in particular is working in close co-operation
with the Wild Company at Heerbrugg, Switzerland. Experience has taught
that this kind of collaboration between manufacturer and user results in advan-
tages for both parties. Examples of these advantages are the improvement of
aerial cameras and the development of gyroscopic control of the vertical,
which latter problem is practically solved.
Calibration of the camera is done by the manufacturer, and each camera
is regularly checked at the Geodetic Institute of the Technical University at
Delft. The principal point, principal distance and disortion are determined by
means of a visual goniometer as described in a publication by R. Roelofs,
"Distortion, principal point, point of symmetry and calibrated principal point
(“Photogrammetria’” 1950/51, page 49).
In the Netherlands special attention is paid to the problems of definitions
relating to aerial survey cameras as shown by the above publication of R.
Roelofs and by the participation of Mr. Corten and the writer of the present
report in the panel discussion on this subject at the Annual Meeting of the
American Society of Photogrammetry in January 1951 in Washington. See
“Photogrammetric Engineering” 1951, pages 401 and 413.
CHAPTER III — AERIAL TRIANGULATION.
Radial Triangulation.
During the past four years no important developments have taken place
in the Netherlands regarding radial triangulation. The situation in the Nether-
lands is therefore about the same as in other countries. This is somewhat
surprising in view of the flatness of the Netherlands and the favourable con-
ditions for this method. It seems that the advantages of this method will only
be economic when the gyroscopic determination of the vertical at the moment
of the exposure is introduced. The precision of the stereoscopic measurement
in such instruments as the radial triangulators of Zeiss and De Koningh can
only be fully exploited if isocentres and nadir points are determined with
sufficient accuracy. A new situation for this method of determining minor
control points will arise if a reliable gyroscope becomes available which can
be connected with normal cameras. As indicated in Chapter II, K.L.M. Aerial
Surveys and Wild are collaborating to find a proper solution for this problem.
Isocentres and nadir points may be determined by parallax measurements in
the stereocomparator instead of using a gyroscope. The formulas for the
second order terms in the relation between the elements of orientation and the
parallax in 6 points will shortly be published in "Photogrammetria". It is
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