26 
the vertical adjustment was omitted. That adjustment will be the subject of a se 
parate publication. 
The analytical strip triangulation [1] features relative orientation of each photo 
graph with respect to the preceding one followed'by a scaling of the resulting model 
that does not disturb the relative orientation. In order to correct for lens distortion, 
refraction, and earth curvature, symmetrical radial corrections are given to the pho 
tograph coordinates. 
This procedure of analytical triangulation is very similar to the procedure of 
instrumental triangulation. However, the result is necessarily independent of the 
direction of triangulation. 
The horizontal block adjustments [2] consisted of conformal transformations of 
the second or third degree, applied to individual strips in an iterative procedure. 
Various numbers of ground control points were used. 
2 — INSTRUMENTS AND MEASURING PROCEDURES 
a) Zeiss Jena 1818 
The Zeiss Jena 1818 Stereocomparator is a relatively simple instrument. The 
measurements were made without any adjustment or calibration. 
This stereocomparator is suitable for the measurement of individual models 
with photograph size up to 180x180 mm. When changing from one model of a 
strip to the next, with the photograph size of 140x140 mm it is possible to leave 
the photograph that is retained undisturbed in its carrier. However, the distance 
between the carriers must be changed by means of a special lead-screw. 
For relative orientation, three points were selected close to the western edge 
of each photograph and measured in each model where they occurred. With a lon 
gitudinal overlap of more than 70%, this gave nine points for the relative orientation 
of each model. In many models where the overlap was considerably larger than 
70%, three more points were measured close to the eastern edge. In a number of 
models where the nine points covered the whole width, three additional points were 
measured farther in from the eastern edge. As a result, twelve points were used for 
the relative orientation of most of the models in the six most northerly strips, and 
nine for that of most of the models in the two most southerly strips. 
The three most westerly points in each model were used for scale transfer. For 
identification purposes, these points and the tie points between strips were pricked 
on the paper prints. 
Each point was pointed at stereoscopically three times, and the average of the 
three readings was recorded manually. 
b) Nistri TA3 
The Nistri TA3 at the National Research Council is one of the first instruments 
of its type that was produced. 
At regular intervals, the cams for the x- and ^/-coordinates were calibrated and 
the rectangularity of the axes was checked. In these respects the instrument proved 
to be very stable. However, repeated measurements of well-defined points often 
showed discrepancies of 20 microns and more. Also, occasional errors occurred in the 
typed coordinates. 
In an attempt to strengthen in particular the azimuth transfer during triangula-