distance derived from scaling of stereo models to the positions obtained from
stereo-template laydown. The results obtained, both in Nigeria and in Canada,
show that the mean square error, relative to the base distance, is 1.27%,
or Îl: 370.
8. CONCLUSIONS
The instruments and methods described in this paper were employed
in Nigeria, Gabon, and Canada on practical mapping projects covering some
2
115,000 km , so the results achieved are indicative of the accuracies that can be
expected from this mapping system under diverse operational conditions. The
results of these surveys support the following conclusions:
(1) The horizon camera permits determination of the tip and tilt of the aerial
camera at the moment of exposure with the same order of accuracy as the
accuracy of relative and absolute orientations of a stereo model based on
ground control
(2) The horizon camera data permits an accurate determination of the nadir
point needed in connection with Aerodist- or Hiran-controlled photography.
(3) The aerial triangulation can be carried out on a simple and relatively
inexpensive instrument, such as a Wild B-8 plotter.
(4) Since the bridging is done with independent pairs, a number of plotting
instruments can be used simultaneously for bridging of the same strip.
(5) The mapping system is independent of the terrain (unlike the A.P.R. system).
(6) The density of the vertical control when mapping a large area is reduced by
as much as 50%, compared with the aero-polygon method.
(7) Because there is no rigid requirement regarding the location of the ground
control within a strip, such control can be established at locations where
the access is best and where good photo identification can be accomplished.
(8) The application of this mapping system makes a new approach to aerial
triangulation feasible. It is no longer necessary to bridge in strips.
Independent stereo models can be combined immediately into blocks and
adjusted. Bridging of blocks can now be directly done, instead of first
bridging strips.
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