-13-
The above equations are to be carefully considered in the course
of designing for mapping projects involving bridging, to make sure that
the expected accuracy of the method -will satisfy the specifications.
Sometimes equations 4 and 10 will indicate that the specified
accuracy cannot be met by aerotriangulation. This is particularly true
in cases involving large scale mapping with very high standards of
accuracy. In such cases, each and every model has to be terrestrially
controlled.
Example:
The following example demonstrates the use of the mbd charts
(Fig. 2 and Fig. 2-a) and the mbd formulae (equations 1 and 2).
Given: A strip of land is to be mapped to the scale of 1:25000
using a photographic strip composed of 9in./9in. photos.
The horizontal accuracy requirements specify that not
more than 10 percent of the points tested shall be in
error by more than l/50in., measured on the publication
scale. The vertical accuracy requirements specify a mean
square error in elevation of +50 ft. or less. The principal
distance of the camera is 8.25 in., and the flight height
above ground is 27000 ft. Longitudinal overlap is 60$.
The accuracy (mean square error) of stereoscopic measure
ment of parallax in the image plane is +0.01 mm. For all
practical purposes, the ground control is to be considered
error-free.
Wanted: Determine the maximum safe bridging distance (mbd) and the
estimated accuracy of deduced elevations ( ).
H