Also the results of the connections on grids confirm the preceding conclusions: they show,
however, the presence of other residual systematic errors in the formation of the model.
The torsion presented by both strips on grids and the general curvature, particularly
evident in the second strip, are due to the systematic errors in x and in co, found in the single
models.
On the contrary, the scale variation, particularly evident in the first strip, and the error in
height, that gradually increases along the strips and appears in both of them, clearly denounce the
presence of a systematic convergence error that cannot be seen in the results of the first part of
the research. However, this error cannot be larger than io", which we can deduce by ascribing
the whole distortion in X of the first strip only to the systematic error of convergence.
On the other hand, we must point out that the total closure errors, which include the effects
both of an eventual disorientation of the first model and of the systematic and accidental errors
in the connection, are very small if compared to the length of the connection itself. Moreover, the
errors of both strips present so regular a behaviour that we are led to suppose that an adjustment
with interpolation formulae of II degree would reduce them to very small values.
What has been deduced so far from the analysis of the strips on grids, can also be deduced
from the study of the behaviours of the orientation elements in the single models. In theory, they
should all be null; on the contrary, in practice, they behave as shown in figures 3 and 4.
We must point out, besides the presence of a systematic error of A<p (decreasing value of b z ),
a remarkable systematic difference in the behaviour of the instrument in the position of «base
in » and « base out ».
The angular elements have variations that, on the average, are larger than i c . Of course, these
variations remarkably influence the orientation elements b x and b z , The cause of these variations
is not very clear, but it is probably related to the systematic measure errors of the plate-coordinates:
for instance, to eventual errors in the measure screw. The variations of the transversal parallaxes
producing in the model a <p variation of i c , are about 5 ¡um. If we consider that in the AP/C
the parallaxes are obtained from the comparison of two coordinates, we can deduce that the
coordinates themselves are affected by an error smaller than 5 ¡um, as guaranteed by the
building firm. In fact, the screws of the AP/C are not provided with a correcting device for
the periodic errors.
In short, these experiments testify that the AP/C has given very good results, which can be
compared with those of a precision plotting apparatus.
3. - The tests on real strips have been executed using the photographic material of Commis
sion B (O.E.E.P.E.), available at the Centro of Milan upon permission of the President of the
Commission, that is strip 2.6.4. of the Reichenbach Polygon, taken at the relative flying height of
1.200 m, with a Wild RC 7 camera, on plates, focal length 100.35 mm > size 150 X 150 mm 2 . The
ground flown over is very uneven with height differences that, within each model, are larger than
20 % of the flying altitude. In the strip area 61 check points marked on the ground have been
uniformly distributed; furthermore, there are several other natural points of known height.
Strip 2.6.4. has been triangulated twice with the same procedure that may be outlined in
the following points.
Interior orientation. - We have obtained it by measuring the coordinates of the four fiducial
marks represented by holes placed nearly in the center of the four sides of the plates; in fact, the
principal point of each plate, to which all the plate coordinates are referred, is that point whose
X coordinate is the mean of the X coordinates of the two fiducial marks placed on the two plate
sides normal to the direction of the X axis and the Y is the mean of the Y coordinates of the
other two fiducial marks. No principal point correction or objective lens distortion have been
introduced into the computation program. In fact, both the correction of the principal point and
the distortion curve given by Wild are very small; moreover, preceding experiments on the same
material let us suppose that the errors in the determination of the distortion be of the same entity
as the average measured distortion.
9