(d) 
(à) 
the other, but it is essential that, when 
adjusting the stereoblock, there should be 
some height control applied to each of its 
component strips, since the internal angle 
conditions in themselves give no Stability 
to prevent one strip having a longitudinal 
"twist" relative to another, 
These heights need not have been provided by 
ground survey for every Stereoblock, since 
they can be carried through from stereoblock 
to stereoblock, Again, it is desirable 
that a certain amount of plan control should 
be available (again it may be carried through 
ffom an adjacent stereoblock), and if it is 
not, the block should be "anchored" by 
arbitrarily fixing one or more coordinates 
(since otherwise the least squares solution 
will be indeterminate), 
Radar or Tellurometer Distance Measurement. 
This may be between two air stations, between 
an air and a ground point, or between two 
ground points; in all cases, the "obsèrved 
quantity" is the distance itself, and the six 
coefficients of dX,dY,d2,dX',dY',aZ' are 
(X-X')/R, (Y-Y')/R, etc. 
where R^ = (x-x')^4 (y-Y*)? 
«(z-z')* 
Star or Sun Observations. It is assumed that 
the heavenly body is photographed, at a known 
time and simultaneously with the mainair photo, 
and that the two cameras are rigidly connected, 
in a previously determined manner, Let the 
astro camera centre have coordinates (X,¥,2) 
in the main photocoordinate system, and let the 
ray from the heavenly body, produced, meet the 
main photo plane in a point whose coordinates 
are (x,y,O); let the heavenly body have direction 
cosines (1l,m,n) at that instant, in the ground 
coordinate scheme, Then one may be considered 
to have an additional photo point, with consequently 
two additional observation equations, the photo 
coordinates of this point being fei and its 
provisional coordinates (U-Wl/n,V-Wm/n,O), so 
that there is no addition to the number of 
variables through having an astro shot.x 
Simultaneous Obliques and Verticals, 
Here again, if the cameras are rigidly connected 
and the relationship known, an oblique photo 
point can be projected on to the main photo plane, 
and then shifted sideways by the amount that the 
oblique camera centre differs from the main camera