PHOTOGRAMMETRIC ENGINEERING 
permits fitting to each band or isolated con- 
trol point, it is possible to fit to a vertical 
control point on which the elevation is in 
error without detecting this error from the 
residual errors. It has been observed on 
numerous extensions that the change in lat- 
eral tilt error between two successive models 
on an extension is usually less than .38 X 107. 
With respect to the adjustment equations 
this means that 
af (xy) of (xv) : 
Ir 2 = 10.38 ¢ 107% 
| Ö(y): Ö(y)i+ | ; Ï 
where: (7) refers to the number of the photo- 
graph and the distance from (7) to (-- 1) is the 
longitudinal dimension of the stereoscopic 
model (approximately, the model base). The 
partial derivative 
(Of (xy)) 
av) 
can obviously be determined as a by-product 
of the solution to the adjustment equation. 
Numerical values are then computed at in- 
equivalent to the longitudinal 
dimension of two stereo-models. The differ- 
tervals in “x” 
ences between consecutive values are ex- 
amined in evaluating the results of the solu- 
tion. Unfortunately only relatively large 
errors can be detected by this method. With 
regard to the longitudinal change in slope, 
there is less consistency than with the lateral 
change in slope. In fact the variation result- 
ing from the use of different cameras ob- 
scures the expected correlation due to flight 
altitude. For this reason, no attempt has been 
made to use the longitudinal slope difference. 
The program described 
operational at the Army Map Service since 
September 1959, It has reduced the graphical 
adjustment to an occasional minor revision 
above has been 
for a computed solution. Furthermore, there 
has been no evidence of excessive flexibility 
which is constantly checked by the differences 
of independently adjusted elevations from 
adjacent strips. 
And now to digress from the discussion of 
the vertical adjustment to another applica- 
tion of the computer, namely, the horizontal 
block adjustment. Despite the intensive use 
made of the independent strip method for 
horizontal and vertical adjustment, the ad- 
vantages of a block adjustment had not been 
overlooked. The problem remained to devise 
a method, both practical and efficient, that 
is compatible with the facilities and equip- 
ment available at Such a 
method for horizontal block adjustment has 
been recently tested at the Army Map Serv- 
our installation. 
6 
ice. The method in principle can most readily 
be described by comparing it with the familiar 
method of Dr. Jerie;! however, the adjustment 
is completely mathematical and was accom- 
plished using existing UNIVAC programs. 
The method and results obtained will now 
be briefly described. 
The strips of photographs are stereotri- 
angulated and then divided into segments of 
at least two models (possibly more) in length. 
Tie points are preselected common to the 
corners of four segments; that is, 
ments each from two adjacent strips. The 
object is to adjust the segments from all of 
two seg- 
the strips on the project area to the best rela- 
tive fit 
net of geodetic control. Such an adjustment 
between segments and also to the 
consists of the simultaneous solution of a set 
(linear 
formal transformation and scale change) for 
of transformation coefficients con- 
each segment by the method of least squares. 
Although theoretically possible, the mathe- 
matical solution for the above problem has its 
computational limitations. The number of 
significant places which must be carried in 
solving for the coefficients of transformation 
make this procedure impractical; therefore, 
the adjustment has been divided into two 
phases. 
The first phase consists of transforming the 
stereophotogrammetric coordinates of each 
strip into the geodetic coordinate system 
using the well-known equations: 
X = A:x — Biy + ( 
(4) 
Y = A:v+Bx+D 
where 
X, Y are the approximate geodetic coor 
y, are the stereophotogram 
B; C; D; are the 
coefficients for strip 1(3=1l, 2, 3 -- n»). 
dinates: x, 
metric coordinates; 4; 
Such a transformation is applied to thc 
stereophotogrammetric coordinates of a base 
strip, which contains at least two geodetie 
control points, thus transforming the coor- 
dinates of control and tie points into the 
geodetic coordinate system. The coordinates 
of the adjacent strips are then consecutively 
transformed into the geodetic coordinate 
system using the adjusted coordinates of two 
tie points from the previously transformed 
NOW 
The strips are approximately 
this time the differences 
strips. 
transformed and at 
between the true geodetic coordinates and the 
t “Block Adjustment by Means of Analogue 
Computers,” by Dr. H. C. Jerie, Photogrammetria, 
Vol. XIV, No. 4, 1957-1958. 
  
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