III. The normal course of work in the plotting instrument. 
IIL1. Fig. 2 shows a series of stereo models marked M, — M,. The overlap of 
the pictures in the strip is presumed to be 60%. In the area in common to two 
adjoining models “monocular connection points” (cp. point 11.2) marked 01” and 
01” were applied between the models 0 and 1, 12’ and 12” between the models i 
and 2 etc. In the first and the last models a geodetically determined point (the 
control points P, and P,) was presumed. In practice there are usually also a num- 
ber of photogrammetric control points i.e. signalled points which are to be deter- 
mined as to their coordinates at the triangulation. 
III.2. Model O is levelled. When dealing with even ground eg. archipelagoes 
or — generally — when inclination quantities are made use of for the levelling 
of the models, this can be executed on an arbitrary scale. When levelling by the 
aid of elevation values, greater scale errors are not tolerated than permit an accu- 
rate calculation of the data for the rotations which are necessary for the levelling 
of the model. The levelling errors, remaining after the rotations must not cause 
such displacements of the connection points, that are dangerous for the triangu- 
lation. The greater difference of level between the connection points the more care 
must consequently be devoted to the determination of the scale. In most cases it is 
possible to determine at least one model in the strip with enough accuracy by 
using the altitude of flight, existing maps or a distance measured on the ground. 
This model can be used as 0-model at the triangulation. 
IIL3. Model coordinates (instrument coordinates) are read for the control point 
Po and the connection points 01” and 01” (possibly 01°). 
In an analogous way are levelled and determined as to their scale all the stereo 
models of the strip and are read the model coordinates for the connection points 
against the immediately preceding and the following model. When setting 
each new pair of pictures in the stereo-instrument the rotation mentioned under 
point II.3 must be executed. The approximate scale is graphically or numerically 
transferred between the models. In the last model the coordinates of the control 
point P, are also read. 
In stereoscopic instruments of the second order, which are usually constructed 
for graphical plotting of separate pairs of pictures only (e.g. Wild Autograph 
Model A6) the connection of the models can be executed either graphically using 
a microscope (cp. Blachut [1]) or graphical-numerically. In the latter case the 
control points and the cross points of each model are plotted on to one paper. 
Because of the rotation of every other pair of pictures at the setting of the photo- 
graphs in the instrument, the paper must also be turned about 200° for each new 
model that is to be plotted. For the rest the points may be plotted on the paper in 
quite arbitrary positions. (To avoid confusion it is wise to mark the plotted points 
with different colours and signs for the different models). When all the models 
are plotted on the paper this is placed in an arbitrary position in a coordinato- 
graph provided with a microscope, and the coordinates are then read in the same 
system for all the points. This is most quickly done by setting the microscope of 
the coordinatograph successively on the points, independent of the question in 
which model they are plotted. The coordinates are, however, recorded in models 
in special calculating forms, 
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