May, 1960 Commission III 183 
entirely with the flying crew and the flight operation is smooth. There is also no 
necessity for expensive establishment of monitoring stations or other ground preparation. 
An additional advantage is the extreme simplicity and reliability of instrumental 
triangulation procedure. The occasional errors committed by the operator on the 
plotter are easy to detect and affect the final accuracy very little. 
Use oF OBLIQUE PHOTOGRAPHS TO CONTROL THE BEND OF TRIANGULATED STRIPS 
This interesting and original method has been greatly simplified by modifying the 
initial procedure. Contrary to the first method presented at the Stockholm Congress, 
the new procedure does not require the construction of one continuous control line 
throughout the strip, but uses independent line segments constructed on individual 
oblique photographs. From a set of three points selected on a straight-line segment, 
the coefficient of the second-order term in a parabolic equation defining the bend of 
the strip can be determined. By using several segments and the method of least squares, 
a higher accuracy is obtained. 
This method was tested on a strip 190 km long with aerial photographs taken 
from 9000 m. The mean square error of the y coordinates checked on 102 ground 
control points, amounted to 7m, = + 9.6 m, with the maximum error Erw = 200m ~ 
ANALYTICAL AERIAL TRIANGULATION 
The study of analytical methods, started in 1953, led to the establishment of a very 
elegant method of analytical triangulation, which was published at the International 
Photogrammetric Congress in Stockholm in 1956. In this method each photograph is 
successively oriented to the preceding photograph, up to 30 points being used. The 
scaling of the resulting model is done separately and independently, because this 
procedure seems to offer theoretical and practical advantages. The method was first 
programmed and tried on the Ferut, a large Ferranti electronic computer. After a few 
experimental trials, however, it was re-programmed for the medium-sized computer 
IBM-650, which is available to research centres as well as to mapping agencies. 
In order to carry out experimental studies with the method, the National Research 
Council purchased the Nistri TA-3 Stereocomparator and triangulated a number of 
strips. As a result, the method is at present in perfect operational condition. It 
consists basically of two steps: (a) computation of the strip coordinates from the 
measured plate coordinates, and (b) transformation of the triangulated strip to the 
ground control system by a three-dimensional linear transformation. 
To this program a second-degree conformal transformation of x and y co- 
ordinates was added to permit the inclusion of up to 50 known ground control points 
in the adjustment of the strip. This last computational routine is extremely practical 
in analytical triangulation projects, and also in any triangulation procedure for which 
the numerical data of triangulated points are known. 
As an example, the results of two strip triangulations performed on the Nistri 
Stereocomparator TA-3 are given in Table IIL 
BLOCK ADJUSTMENTS 
Recently the so-called “block adjustment” problem has been satisfactorily solved 
by using a numerical computation method. When several overlapping parallel strips 
are triangulated, together they form an entity covering a certain area. Each triangu- 
lated strip must be fitted into the ground control system in the best possible way and 
the discrepancies between adjoining strips must be adjusted. This complex problem 
was solved by using second-degree conformal transformation of strips in an iterative 
process, in which ground control points and the tie point of adjoining strips are