éd et profile
wa; mm o 0| mmm —— — — ~ - X
t
—+— Suitable bridging
distance
EU l..i-l. I1.
Fig. à
In comparison with the first method, such an arrangement
of the radar profiles reduces their number considerably, although |
it does not reduce the amount of work which must be done on the
plotting machines, since the data necessary for a detailed plotting
must first be obtained by aerotriangulation. There are cases,
however, such as when the type of terrain makes precise navigation
impossible, when this is the only practical method.
In order to increase the general accuracy, a combination
of both methods can be used. If there are only a few widely spaced
fixed points in the area, a system of nodal points adds considerable
strength to the established network of vertical controls.
And finally there is the third possibility of applying
the radar profile to photogrammetry by making it an integral part
of the aerotriangulation method. When working on the piotting
machines, use would therefore be made of the data contained in the
radar profile, such as the differences in the altitude of the air-
craft above the ground; the elevations deduced from the radar profile
will also be used later as a basis of adjustment. In comparing the
radar profile with the aerotriangulation, the following difference
becomes obvious: although aerotriangulation itself may have great
inner accuracy, various types of systematic and pseudo-systematic
errors and the occurrence of "breaks" due, for instance, to some
kind of irregularity in a photograph, lead to a rapid increase in
the values of the absolute error, thus reducing the accuracy and
efficiency of the method. In contrast to this, the radar profile
possesses a high degree of "general" accuracy within wide climatolo-
gical limits, but a limited "inner" accuracy in the representation
of neighbouring points of the profile. By integrating the inner
accuracy of aerotriangulation with the general accuracy of the radar
profile, a favourable combination of the two methods for the purpose
