REVIEW OF STRIP AND BLOCK ADJUSTMENT DURING 1964-1967 
9 
of the polynomials as low as possible. Restric 
tion to the second degree is possible by divid 
ing long strips into sections. Such sections 
can be transformed by means of either inde 
pendent polynomials or composed poly 
nomials. 
An investigation of the present writer [39] 
has shown that with fairly sparse control the 
block adjustment of models does not give a 
better absolute accuracy than the block ad 
justment of strips. Soehngen [87] has obtained 
better results with the height adjustment of 
models. However, he uses a larger number 
and well-located control points. 
Subblocks, and External 
Block Adjustment 
Anderson [95, 96] describes the computa 
tion of subblocks of 3 X 3 or m X n photographs 
with 60 percent longitudinal and lateral over 
lap and their assembly into a block by means 
of similarity transformations. For the inter 
nal adjustment of such an assembly, the 
method of Roelofs [47] would seem to be very 
suitable. 
For the adjustment to ground control of 
an internally adjusted block, polynomial 
transformations of the block coordinates 
could be used. However, with a low degree of 
the transformations one can hardly expect to 
obtain a good fit at all ground-control points 
and with high degrees one may obtain too 
large errors in uncontrolled areas. A second- 
degree transformation may be suitable for an 
initial positioning of the block and to enable 
the final block adjustment to be performed 
separately for the three coordinates. 
Arthur [97] describes an interpolation 
method for such an adjustment. However, 
this method does not give a solution in the 
case of four ground-control points situated at 
the corners of a square. Since this should be 
a well-defined case, the suitability of the 
method in other cases requires careful ex 
amination. 
Vlcek [98] and Wainauskas [99] describe 
the use of orthogonal polynomials. The only 
advantage of their use appears to be that it 
may be possible to identify and reject terms 
that do not contribute significantly to an 
improvement of the fit at the control points. 
Accuracy of Strip and 
Block Adjustment 
Ackermann and Jerie, [100] to [107], have 
investigated the theoretical accuracy of strip 
and block adjustment, assuming that sys 
tematic errors are either absent or have been 
eliminated. They deal with the adjustment by 
means of similarity transformation of models 
and, for the height adjustment, also the ITC- 
Jerie analog adjustment. 
It is of particular interest that Ackermann 
[100] finds that in his investigations the sim 
ilarity transformation of models and the 
second- or third-degree polynomial strip 
transformation give about equivalent results. 
In a practical test an adjustment of a 
block of 180 photographs with 60 percent 
longitudinal and lateral overlap by the U. S. 
Coast and Geodetic Survey [10] has produced 
root-mean-square values of the residuals at 
check points of only nine microns at photo 
graph scale. 
The polynomial adjustment of strips with 
normal lateral overlap gives values that 
usually vary between 25 and 60 microns. [39]. 
Jacobs [81], using analytical triangulation 
and the Coast and Geodetic Survey’s correc 
tions for film deformation, obtains values of 
around 15 microns. 
Conclusion 
Prof. Schermerhorn’s statement that the 
methodical development of mathematics and 
programming procedures in analytical tri 
angulation seems to be complete [2] can now 
be extended to strip and block adjustment. 
Still, further refinements, modifications, and 
simplifications of present procedures will un- 
undoubtedly continue to appear. 
For instance, one can expect that more 
work will be done on the construction of 
economical direct and iterative solutions of 
the large systems of normal equations which 
occur in the adjustment of photographs and 
of models. In this field a more than four-year- 
old claim by members of the ITC that an 
exceptionally economical direct solution is 
possible by a suitable arrangement of the 
unknowns still awaits clarification. Brown 
[lib] has recently made a rather similar 
claim concerning the iterative solution. In 
addition, the use of the method of conjugate 
gradients and of related methods may war 
rant further investigation. 
In the field of analytical triangulation, the 
simultaneous triangulation of all photographs 
of a strip in an arbitrary system should not 
be much more complicated than the triplet 
triangulation and could with advantage re 
place the latter. 
The adjustment of internally adjusted 
strips and blocks to ground control should be 
further investigated. This may provide a 
very suitable procedure especially for small 
computers and where the utmost in accuracy 
is not needed.