Estimated X- and Y-coordinates of points at the beginning and end of the strips
have been used as horizontal control in the levelling. Where neighbouring strips had
been levelled already, transformed coordinates from these strips have been used also.
The coordinates of strip tie points have been compared and points affected by reading
errors or identification discrepancies have been eliminated.
4. — Block adjustment
The block adjustment consists in trasformation of the X- and Y-coordinates of
each strip by means fo second degree conformal transformations. Ground control
points and tie points with overlapping strips can be employed in any number and in
any location in a strip. All tie points are given the same weight; ground control points
can be given different weights.
An iterative procedure is used in which the sequence in which the strips are adju-
sted and the choice of control points can be varied at will. This procedure has been
chosen because a program for second degree conformal transformation had already
been coded and little time was available for developing the block adjustment program.
Eventually a third degree conformal transformation may be used, and a simultaneous
adjustment of all strips.
The ground control points have been chosen in pairs of two, to have a check on
errors. Four different adjustments have been planned, each with more ground control
than the preceding one. The first adjustment will make use of two ground control points
in each of the four corners of the block. The second will in addition make use of two
control points near the middle of the Western edge and near the middle of the Eastern
edge. The third will also use two ground control points near the middle of the Northern
and the Southern edge. The fourth will in addition use two ground control points
near the centre of the block.
The number of usable tie points in the overlap between strips ranges from 18 to
25. In order to obtain a more balanced distribution of tie points, from 18 to 21 will
be used in the block adjustment.
Complete results of the block adjustment will be available when the Congress
meets. At the time of writing of this report preliminary results only are available.
The levelled strips have been transformed to the system of strip 8 by means of second
degree conformal transformations in which all designated tie points have been emplo-
yed. Subsequently the resulting block has been transformed as a whole by means of
the same type of transformation, using the ground control points in the four corners:
3, 5, 40, 41, 271, 275, 297 and 299 ».
Western Germany Centre. — Prof. Foerstner has sent us the report on the program
and the present stage of works. Most of it, is reported here below:
«1. — In July 1959 an area of 80 km x 80 km in France was surveyed by the
Institut Geographique National (I.G.N., Paris). For these flights Germany offered
a ZEISS Camera R.M.K. 15-23 with statoscope and an air photographer. The photo-
graphs of the ZEISS Camera were taken on PERUTZ-PERVOLA-Film and deve-
loped immediately after the flight by the I.G.N. in a developing equipment offered
by the ZEISS-AEROTOPOGRAPH Company. The pictures show an overlap of 90
per cent.
2. — By means of a tracing paper indicating the centre of the photograph
Dr. Brucklacher selected the pictures required for triangulation (a total of 188). Spe-
cial attention was given to the fact that the base component b, within the strips had
34
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