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A collimator C was placed on the plate-carrier with the line of
vision as near as possible parallel to the X direction. A theodolite T
was placed on a fixed mounting next to the instrument. The secund-
ary rotations of the plate-carrier during the X-movement could now be
I-
measured by pointing the theodolite to the collimator mark and
reading the horizontal circle (to the nearest dmgr).
These measurements were carried out for the 3, in Delft available,
radial-triangulators. The results are given in fig. 5.
Referring to these graphs the following comments can be made:
1. At the estimation of the influence of the obtained errors the fact
has to be taken into account that each measurement of a direction
is executed in tzvo positions of the plate-carrier so that the two X
positions are always symmetrical with respect to the centre which
is indicated in fig. 5. Hence^ when the curve is polar symmetrical
with respect to this centre, as e.g. with curve b is approximately
the case, then the error is practically eliminated in the mean value
of the two positions.
2. In the curves c, d, e and there seems to be a certain periodicity.
A closer examination reveals that the frequency of this periodicity
corresponds with the circumference of the wheels on which the
carrier rests. The method by which the carrier is guided along
the rule (see fig. 6) shows that each excentricity of the axes of
one of these wheels will cause horizontal displacements and there
fore secundary rotations.
3. To give an idea of the influence of the secundary rotations on the
results of a triangulation, in fig. 7 the errors are represented (in
dmgr) in consequence of the use of triangulator „De Koningh nr
3985". The letters L and R indicate that the directions were
measured in the left resp. right plate-carrier. The same errors
are consequently repeated after each pair of rhomboids.
The closing errors of the two rhomboids are resp. 24,4 and
22,8 units of the fifth place of the logarithms.
The resulting errors after the adjustment of the sinus condition
are represented in fig 8 (also in dmgr). The influence of these
resulting errors on the computed co-ordinates is very small. They
X
Fig. 4
