x If this requirement seems excessive, it should be 
Dc rne in mind that only one pair of photographs 
eeds to have three known points, since coordinates 
can then be transferred from photograph to photograph 
throughout the block, 
xx In point of fact the value of H is not known, and is 
  
4 
in fact irrelevant at 
however, this stage o 
one for gett ing the p 
which one retur 
convenient val 
after 
any 
So 
this 
f leve 
hoto 
ns to 
ue 
stage, in the oblique case; 
lling is only an intermediate 
coordinates of the plumb point, 
the original ground coordinates, 
be used, 
(3 
may be 
  
  
    
  
  
4, Block Formation 
[he role of the si | in block adjustment is 
exactly that of the individual photograph in  etereoblock 
adjustment; the points whose provisional coordinates are 
to be varied are NOW the tie points between stereoblocks 
(and any ground control it is desired to include), and the 
"observed quantities". from which observa tion equations are 
formed exactly as before, are space angles subtended by two 
of the points at a third, all within the same stereoblock, 
Thus, the angular relations within the stereob lock are to be 
preserved, as far as may be, but the whole is allowed to 
stretch and shift to adjust itself to neighbouring stereoblocks, 
If there are n tie and control points within a stereoblock, 
then there are just (3n-7) independent observation equations 
corresponding to them, The space angles to derive them are 
best selected by starting with three points (two conditions 
between them) and "intersecting" every other point by 
three space angles from these three; rejections will then 
only be troublesome if one of the original three points is bad, 
If there are still too many variables to form the whole 
block directly, a further intermedi stages) of 
"Super-stereoblocks" can of course i. Alternativel; 
the adjusted stereoblocks would, immediately 
suitable fo 
5 External Conditions 
The stereobl 
account of all types of 
earlier, may be flexible, 
or rigid, and reduce 
Examples 
  
.Ock adjustm 
external controls, 
the number 
  
  
ad JUs tme nt, 
nent 
lent process is capable of 
which sy as 
observation 
variables, 
taking 
noted 
equations, 
he 
LLC 
add to t 
of 
and 
(a) Plan and Height Control; dealt with earlier, (ith 
these, and in fact any of the controls, it isa 
matter of choice whether all are applied at the 
stereoblock adjustment stage, or the block form- 
ation stage, or both, or some at one and some at